[PATCH v10 0/6] Enable automatic SVN updates for SGX enclaves

[PATCH v10 0/6] Enable automatic SVN updates for SGX enclaves

[Elena Reshetova]

Changes since v9 following reviews by Kai:

 - postpone the definition of sgx_inc_usage_count
 until patch 6
 - clarify the commit message in patch 6
 - minor fixes

Note: I didn't merge patch 1 and 2 since it goes against
previous suggestion made by Jarkko.

Changes since v8 following reviews by Dave and Jarkko:

 - fix the sgx_inc/dec_usage_count() to not do any
 actual counting until the later patch when adequate
 mutex is introduced as suggested by Dave
 - add an additional patch (patch 1) to redefine
 existing sgx_(vepc_)open into wrappers to allow
 the follow up patch to introduce the sgx_inc/dec_usage_count()
 functions into sgx_(vepc_)open cleanly as suggested
 by Jarkko. 

Changes since v7 following reviews by Dave:

 - change sgx_usage_count to be a normal int type
 and greatly simplify the sgx_inc_usage_count func.
 This results in requiring a mutex for each sgx_(vepc_)open
 but given that the mutex is held a short amount of
 time it should be ok perf-wise.

Changes since v6 following reviews by Kai,Jarkko
and Dave:

 - fix sgx_update_svn function description
 - add maybe_unused for sgx_update_svn in patch 4
 to silence the warning, remove it in patch 5
 - add note to patch 1 explaining why the prototype
 sgx_inc_usage_count returns int and not void
 - fix the order of return code checks in 
 sgx_update_svn
 - cosmetic fixes
 
Note: I didn't change the sgx_inc/dec_usage_count
to statics because they are called from a number of
different code locations and also rely on a static
sgx_usage_count, which lives naturally in main.c.  
 
Changes since v5 following reviews by Ingo, Kai,
Jarkko and Dave:

 - rebase on x86 tip
 - patch 1 is fixed to do correct unwinding in
 case of errors
 - patch 2: add feature flag to cpuid-deps.c
 - patch 3: remove unused SGX_EPC_NOT_READY error code
 - patch 4: fix x86 feature check, return -EAGAIN
 on SGX_INSUFFICIENT_ENTROPY and -EIO on other non-
 expected errors. Comments/style are also fixed.
 - patch 5: rewrite commit message, add comments inline

Changes since v4 following reviews by Dave and Jarkko:

 - breakdown the single patch into 4 patches as
 suggested by Dave
 - fix error unwinding in sgx_(vepc_)open as 
 suggested by Jarkko
 - numerous code improvements suggested by Dave
 - numerous additional code comments and commit
 message improvements as suggested by Dave
 - switch to usage of atomic64_t for sgx_usage_count
 to ensure overflows cannot happen as suggested by Dave
 - do not return a error case when failing with
 SGX_INSUFFICIENT_ENTROPY, fail silently as suggested
 by Dave

Changes since v3 following reviews by Kai and Sean:

 - Change the overall approach to the one suggested
  by Sean and do the EUPDATESVN execution during
  sgx_open() and sgx_vepc_open().
  Note, I do not try to do EUPDATESVN during the release()
  flows since it doesnt save any noticable amount
  of time during next open flow per underlying EUPDATESVN
  microcode logic.
 - In sgx_update_svn() remove the check that we are
  running under VMM and expect the VMM to instead
  expose correct CPUID
 - Move the actual CPUID leaf check out of
  sgx_update_svn() into sgx_init()
 - Use existing RDRAND_RETRY_LOOPS define instead of 10
 - Change the sgx_update_svn() to return 0 only in
 success cases (or if unsupported)
 - Various smaller cosmetic fixes

The still to be discussed question is what sgx_update_svn()
should return in case of various failures. The current version
follows suggestion by Kai and would return an error (and block
sgx_(vepc_)open() in all cases, including running out of entropy.
I think this might be the correct approach for SGX_INSUFFICIENT_ENTROPY
since in such cases userspace can retry the open() and also
will get an info about what is actually blocking the EUPDATEVSN
(and can act on this). However, this is a change in existing API
and therefore debatable and I would like to hear people's feedback.

Changes since v2 following review by Jarkko:

 - formatting of comments is fixed
 - change from pr_error to ENCLS_WARN to communicate errors from
 EUPDATESVN
 - In case an unknown error is detected (must not happen per spec),
 make page allocation from EPC fail in order to prevent EPC usage

Changes since v1 following review by Jarkko:

 - first and second patch are squashed together and a better
   explanation of the change is added into the commit message
 - third and fourth patch are also combined for better understanding
   of error code purposes used in 4th patch
 - implementation of sgx_updatesvn adjusted following Jarkko's 
   suggestions
 - minor fixes in both commit messages and code from the review
 - dropping co-developed-by tag since the code now differs enough
   from the original submission. However, the reference where the
   original code came from and credits to original author is kept

Background
----------

In case an SGX vulnerability is discovered and TCB recovery
for SGX is triggered, Intel specifies a process that must be
followed for a given vulnerability. Steps to mitigate can vary
based on vulnerability type, affected components, etc.
In some cases, a vulnerability can be mitigated via a runtime
recovery flow by shutting down all running SGX enclaves,
clearing enclave page cache (EPC), applying a microcode patch
that does not require a reboot (via late microcode loading) and
restarting all SGX enclaves.


Problem statement
-------------------------
Even when the above-described runtime recovery flow to mitigate the
SGX vulnerability is followed, the SGX attestation evidence will
still reflect the security SVN version being equal to the previous
state of security SVN (containing vulnerability) that created
and managed the enclave until the runtime recovery event. This
limitation currently can be only overcome via a platform reboot,
which negates all the benefits from the rebootless late microcode
loading and not required in this case for functional or security
purposes.


Proposed solution
-----------------

SGX architecture introduced  a new instruction called EUPDATESVN [1]
to Ice Lake. It allows updating security SVN version, given that EPC
is completely empty. The latter is required for security reasons
in order to reason that enclave security posture is as secure as the
security SVN version of the TCB that created it.

This series enables opportunistic execution of EUPDATESVN upon first
EPC page allocation for a first enclave to be run on the platform.

This series is partly based on the previous work done by Cathy Zhang
[2], which attempted to enable forceful destruction of all SGX
enclaves and execution of EUPDATESVN upon successful application of
any microcode patch. This approach is determined as being too
intrusive for the running SGX enclaves, especially taking into account
that it would be performed upon *every* microcode patch application
regardless if it changes the security SVN version or not (change to the
security SVN version is a rare event).

Testing
-------

Tested on EMR machine using kernel-6.16.0_rc7 & sgx selftests.
Also tested on a Kaby Lake machine without EUPDATESVN support.
If Google folks in CC can test on their side, it would be greatly appreciated.


References
----------

[1] https://cdrdv2.intel.com/v1/dl/getContent/648682?explicitVersion=true
[2] https://lore.kernel.org/all/20220520103904.1216-1-cathy.zhang@intel.com/


Elena Reshetova (6):
  x86/sgx: Convert sgx_(vepc_)open to __sgx_(vepc_)open
  x86/sgx: Introduce functions to count the sgx_(vepc_)open()
  x86/cpufeatures: Add X86_FEATURE_SGX_EUPDATESVN feature flag
  x86/sgx: Define error codes for use by ENCLS[EUPDATESVN]
  x86/sgx: Implement ENCLS[EUPDATESVN]
  x86/sgx: Enable automatic SVN updates for SGX enclaves

 arch/x86/include/asm/cpufeatures.h       |  1 +
 arch/x86/include/asm/sgx.h               | 37 ++++++-----
 arch/x86/kernel/cpu/cpuid-deps.c         |  1 +
 arch/x86/kernel/cpu/scattered.c          |  1 +
 arch/x86/kernel/cpu/sgx/driver.c         | 19 +++++-
 arch/x86/kernel/cpu/sgx/encl.c           |  1 +
 arch/x86/kernel/cpu/sgx/encls.h          |  5 ++
 arch/x86/kernel/cpu/sgx/main.c           | 82 ++++++++++++++++++++++++
 arch/x86/kernel/cpu/sgx/sgx.h            |  3 +
 arch/x86/kernel/cpu/sgx/virt.c           | 20 +++++-
 tools/arch/x86/include/asm/cpufeatures.h |  1 +
 11 files changed, 154 insertions(+), 17 deletions(-)

-- 
2.45.2

[PATCH v10 1/6] x86/sgx: Convert sgx_(vepc_)open to __sgx_(vepc_)open

[Elena Reshetova]

In order to introduce the counting of active sgx users on top
of clean functions that allocate vepc structures, covert existing
sgx_(vepc_)open to __sgx_(vepc_)open. Later patch will introduce the
top level wrappers that manage the usage count.

No functional change intended in this patch.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 arch/x86/kernel/cpu/sgx/driver.c | 4 ++--
 arch/x86/kernel/cpu/sgx/virt.c   | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
index 7f8d1e11dbee..9aa48f455c54 100644
--- a/arch/x86/kernel/cpu/sgx/driver.c
+++ b/arch/x86/kernel/cpu/sgx/driver.c
@@ -14,7 +14,7 @@ u64 sgx_attributes_reserved_mask;
 u64 sgx_xfrm_reserved_mask = ~0x3;
 u32 sgx_misc_reserved_mask;
 
-static int sgx_open(struct inode *inode, struct file *file)
+static int __sgx_open(struct inode *inode, struct file *file)
 {
 	struct sgx_encl *encl;
 	int ret;
@@ -126,7 +126,7 @@ static long sgx_compat_ioctl(struct file *filep, unsigned int cmd,
 
 static const struct file_operations sgx_encl_fops = {
 	.owner			= THIS_MODULE,
-	.open			= sgx_open,
+	.open			= __sgx_open,
 	.release		= sgx_release,
 	.unlocked_ioctl		= sgx_ioctl,
 #ifdef CONFIG_COMPAT
diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
index 7aaa3652e31d..d8fdf7f39215 100644
--- a/arch/x86/kernel/cpu/sgx/virt.c
+++ b/arch/x86/kernel/cpu/sgx/virt.c
@@ -258,7 +258,7 @@ static int sgx_vepc_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
-static int sgx_vepc_open(struct inode *inode, struct file *file)
+static int __sgx_vepc_open(struct inode *inode, struct file *file)
 {
 	struct sgx_vepc *vepc;
 
@@ -291,7 +291,7 @@ static long sgx_vepc_ioctl(struct file *file,
 
 static const struct file_operations sgx_vepc_fops = {
 	.owner		= THIS_MODULE,
-	.open		= sgx_vepc_open,
+	.open		= __sgx_vepc_open,
 	.unlocked_ioctl	= sgx_vepc_ioctl,
 	.compat_ioctl	= sgx_vepc_ioctl,
 	.release	= sgx_vepc_release,
-- 
2.45.2

Re: [PATCH v10 1/6] x86/sgx: Convert sgx_(vepc_)open to __sgx_(vepc_)open

[Dave Hansen]

On 8/1/25 04:25, Elena Reshetova wrote:
> In order to introduce the counting of active sgx users on top
> of clean functions that allocate vepc structures, covert existing
> sgx_(vepc_)open to __sgx_(vepc_)open. Later patch will introduce the
> top level wrappers that manage the usage count.
> 
> No functional change intended in this patch.

I'm not following at all why this patch is needed. It looks like pure
unneeded churn to me.

RE: [PATCH v10 1/6] x86/sgx: Convert sgx_(vepc_)open to __sgx_(vepc_)open

[Reshetova, Elena]

 
> On 8/1/25 04:25, Elena Reshetova wrote:
> > In order to introduce the counting of active sgx users on top
> > of clean functions that allocate vepc structures, covert existing
> > sgx_(vepc_)open to __sgx_(vepc_)open. Later patch will introduce the
> > top level wrappers that manage the usage count.
> >
> > No functional change intended in this patch.
> 
> I'm not following at all why this patch is needed. It looks like pure
> unneeded churn to me.

I am happy to merge this into patch 2 if there are no objections. 
Jarkko originally wanted these two patches separated for clarity, so
I followed his suggestion. 

Best Regards,
Elena.

[PATCH v10 2/6] x86/sgx: Introduce functions to count the sgx_(vepc_)open()

[Elena Reshetova]

Currently SGX does not have a global counter to count the
active users from userspace or hypervisor. Define placeholder
functions sgx_inc/dec_usage_count that are used to increment
and decrement such a counter. Also, wire the call sites for
these functions.

The definition of the counter itself and the actual implementation
of these two functions comes next. The counter will be used by
the driver that would be attempting to call EUPDATESVN SGX instruction
only when incrementing from zero.

Note: the sgx_inc_usage_count prototype is defined to return
int for the cleanliness of the follow-up patches. When the
EUPDATESVN SGX instruction will be enabled in the follow-up patch,
the sgx_inc_usage_count will start to return int.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 arch/x86/kernel/cpu/sgx/driver.c | 19 ++++++++++++++++++-
 arch/x86/kernel/cpu/sgx/encl.c   |  1 +
 arch/x86/kernel/cpu/sgx/main.c   | 10 ++++++++++
 arch/x86/kernel/cpu/sgx/sgx.h    |  3 +++
 arch/x86/kernel/cpu/sgx/virt.c   | 20 +++++++++++++++++++-
 5 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
index 9aa48f455c54..79d6020dfe9c 100644
--- a/arch/x86/kernel/cpu/sgx/driver.c
+++ b/arch/x86/kernel/cpu/sgx/driver.c
@@ -41,6 +41,23 @@ static int __sgx_open(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static int sgx_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	ret = sgx_inc_usage_count();
+	if (ret)
+		return ret;
+
+	ret = __sgx_open(inode, file);
+	if (ret) {
+		sgx_dec_usage_count();
+		return ret;
+	}
+
+	return 0;
+}
+
 static int sgx_release(struct inode *inode, struct file *file)
 {
 	struct sgx_encl *encl = file->private_data;
@@ -126,7 +143,7 @@ static long sgx_compat_ioctl(struct file *filep, unsigned int cmd,
 
 static const struct file_operations sgx_encl_fops = {
 	.owner			= THIS_MODULE,
-	.open			= __sgx_open,
+	.open			= sgx_open,
 	.release		= sgx_release,
 	.unlocked_ioctl		= sgx_ioctl,
 #ifdef CONFIG_COMPAT
diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 279148e72459..3b54889ae4a4 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -765,6 +765,7 @@ void sgx_encl_release(struct kref *ref)
 	WARN_ON_ONCE(encl->secs.epc_page);
 
 	kfree(encl);
+	sgx_dec_usage_count();
 }
 
 /*
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 2de01b379aa3..3a5cbd1c170e 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -917,6 +917,16 @@ int sgx_set_attribute(unsigned long *allowed_attributes,
 }
 EXPORT_SYMBOL_GPL(sgx_set_attribute);
 
+int sgx_inc_usage_count(void)
+{
+	return 0;
+}
+
+void sgx_dec_usage_count(void)
+{
+	return;
+}
+
 static int __init sgx_init(void)
 {
 	int ret;
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index d2dad21259a8..f5940393d9bd 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -102,6 +102,9 @@ static inline int __init sgx_vepc_init(void)
 }
 #endif
 
+int sgx_inc_usage_count(void);
+void sgx_dec_usage_count(void);
+
 void sgx_update_lepubkeyhash(u64 *lepubkeyhash);
 
 #endif /* _X86_SGX_H */
diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
index d8fdf7f39215..b649c0610019 100644
--- a/arch/x86/kernel/cpu/sgx/virt.c
+++ b/arch/x86/kernel/cpu/sgx/virt.c
@@ -255,6 +255,7 @@ static int sgx_vepc_release(struct inode *inode, struct file *file)
 	xa_destroy(&vepc->page_array);
 	kfree(vepc);
 
+	sgx_dec_usage_count();
 	return 0;
 }
 
@@ -273,6 +274,23 @@ static int __sgx_vepc_open(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static int sgx_vepc_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	ret = sgx_inc_usage_count();
+	if (ret)
+		return ret;
+
+	ret =  __sgx_vepc_open(inode, file);
+	if (ret) {
+		sgx_dec_usage_count();
+		return ret;
+	}
+
+	return 0;
+}
+
 static long sgx_vepc_ioctl(struct file *file,
 			   unsigned int cmd, unsigned long arg)
 {
@@ -291,7 +309,7 @@ static long sgx_vepc_ioctl(struct file *file,
 
 static const struct file_operations sgx_vepc_fops = {
 	.owner		= THIS_MODULE,
-	.open		= __sgx_vepc_open,
+	.open		= sgx_vepc_open,
 	.unlocked_ioctl	= sgx_vepc_ioctl,
 	.compat_ioctl	= sgx_vepc_ioctl,
 	.release	= sgx_vepc_release,
-- 
2.45.2

Re: [PATCH v10 2/6] x86/sgx: Introduce functions to count the sgx_(vepc_)open()

[Dave Hansen]

On 8/1/25 04:25, Elena Reshetova wrote:
> Note: the sgx_inc_usage_count prototype is defined to return
> int for the cleanliness of the follow-up patches. When the
> EUPDATESVN SGX instruction will be enabled in the follow-up patch,
> the sgx_inc_usage_count will start to return int.

Please use parenthesis for function_names().

Second, sgx_inc_usage_count() _already_ returns 'int'. Now. In this patch.

So I'm confused what this is trying to say.

Is this trying to say that sgx_inc_usage_count() always returns success
(0) for now, but the future implementation can fail? *That's* why it
needs to have an 'int' return type.

RE: [PATCH v10 2/6] x86/sgx: Introduce functions to count the sgx_(vepc_)open()

[Reshetova, Elena]

> -----Original Message-----
> From: Hansen, Dave <dave.hansen@intel.com>
> Sent: Friday, August 1, 2025 7:45 PM
> To: Reshetova, Elena <elena.reshetova@intel.com>
> Cc: jarkko@kernel.org; seanjc@google.com; Huang, Kai
> <kai.huang@intel.com>; mingo@kernel.org; linux-sgx@vger.kernel.org; linux-
> kernel@vger.kernel.org; x86@kernel.org; Mallick, Asit K
> <asit.k.mallick@intel.com>; Scarlata, Vincent R <vincent.r.scarlata@intel.com>;
> Cai, Chong <chongc@google.com>; Aktas, Erdem <erdemaktas@google.com>;
> Annapurve, Vishal <vannapurve@google.com>; Bondarevska, Nataliia
> <bondarn@google.com>; Raynor, Scott <scott.raynor@intel.com>
> Subject: Re: [PATCH v10 2/6] x86/sgx: Introduce functions to count the
> sgx_(vepc_)open()
> 
> On 8/1/25 04:25, Elena Reshetova wrote:
> > Note: the sgx_inc_usage_count prototype is defined to return
> > int for the cleanliness of the follow-up patches. When the
> > EUPDATESVN SGX instruction will be enabled in the follow-up patch,
> > the sgx_inc_usage_count will start to return int.
> 
> Please use parenthesis for function_names().

Sure, will fix. 

> 
> Second, sgx_inc_usage_count() _already_ returns 'int'. Now. In this patch.
> 
> So I'm confused what this is trying to say.
> 
> Is this trying to say that sgx_inc_usage_count() always returns success
> (0) for now, but the future implementation can fail? *That's* why it
> needs to have an 'int' return type.

Yes, I will rephrase this better. 

Best Regards,
Elena.

[PATCH v10 3/6] x86/cpufeatures: Add X86_FEATURE_SGX_EUPDATESVN feature flag

[Elena Reshetova]

Add a flag indicating whenever ENCLS[EUPDATESVN] SGX instruction
is supported. This will be used by SGX driver to perform CPU
SVN updates.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 arch/x86/include/asm/cpufeatures.h       | 1 +
 arch/x86/kernel/cpu/cpuid-deps.c         | 1 +
 arch/x86/kernel/cpu/scattered.c          | 1 +
 tools/arch/x86/include/asm/cpufeatures.h | 1 +
 4 files changed, 4 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 602957dd2609..830d24ff1ada 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -494,6 +494,7 @@
 #define X86_FEATURE_TSA_SQ_NO		(21*32+11) /* AMD CPU not vulnerable to TSA-SQ */
 #define X86_FEATURE_TSA_L1_NO		(21*32+12) /* AMD CPU not vulnerable to TSA-L1 */
 #define X86_FEATURE_CLEAR_CPU_BUF_VM	(21*32+13) /* Clear CPU buffers using VERW before VMRUN */
+#define X86_FEATURE_SGX_EUPDATESVN	(21*32+14) /* Support for ENCLS[EUPDATESVN] instruction */
 
 /*
  * BUG word(s)
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 46efcbd6afa4..3d9f49ad0efd 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -79,6 +79,7 @@ static const struct cpuid_dep cpuid_deps[] = {
 	{ X86_FEATURE_SGX_LC,			X86_FEATURE_SGX	      },
 	{ X86_FEATURE_SGX1,			X86_FEATURE_SGX       },
 	{ X86_FEATURE_SGX2,			X86_FEATURE_SGX1      },
+	{ X86_FEATURE_SGX_EUPDATESVN,		X86_FEATURE_SGX1      },
 	{ X86_FEATURE_SGX_EDECCSSA,		X86_FEATURE_SGX1      },
 	{ X86_FEATURE_XFD,			X86_FEATURE_XSAVES    },
 	{ X86_FEATURE_XFD,			X86_FEATURE_XGETBV1   },
diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index b4a1f6732a3a..d13444d11ba0 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -42,6 +42,7 @@ static const struct cpuid_bit cpuid_bits[] = {
 	{ X86_FEATURE_PER_THREAD_MBA,		CPUID_ECX,  0, 0x00000010, 3 },
 	{ X86_FEATURE_SGX1,			CPUID_EAX,  0, 0x00000012, 0 },
 	{ X86_FEATURE_SGX2,			CPUID_EAX,  1, 0x00000012, 0 },
+	{ X86_FEATURE_SGX_EUPDATESVN,		CPUID_EAX, 10, 0x00000012, 0 },
 	{ X86_FEATURE_SGX_EDECCSSA,		CPUID_EAX, 11, 0x00000012, 0 },
 	{ X86_FEATURE_HW_PSTATE,		CPUID_EDX,  7, 0x80000007, 0 },
 	{ X86_FEATURE_CPB,			CPUID_EDX,  9, 0x80000007, 0 },
diff --git a/tools/arch/x86/include/asm/cpufeatures.h b/tools/arch/x86/include/asm/cpufeatures.h
index ee176236c2be..78c3894c17c1 100644
--- a/tools/arch/x86/include/asm/cpufeatures.h
+++ b/tools/arch/x86/include/asm/cpufeatures.h
@@ -487,6 +487,7 @@
 #define X86_FEATURE_PREFER_YMM		(21*32+ 8) /* Avoid ZMM registers due to downclocking */
 #define X86_FEATURE_APX			(21*32+ 9) /* Advanced Performance Extensions */
 #define X86_FEATURE_INDIRECT_THUNK_ITS	(21*32+10) /* Use thunk for indirect branches in lower half of cacheline */
+#define X86_FEATURE_SGX_EUPDATESVN	(21*32+14) /* Support for ENCLS[EUPDATESVN] instruction */
 
 /*
  * BUG word(s)
-- 
2.45.2

Re: [PATCH v10 3/6] x86/cpufeatures: Add X86_FEATURE_SGX_EUPDATESVN feature flag

[Dave Hansen]

On 8/1/25 04:25, Elena Reshetova wrote:
> Add a flag indicating whenever ENCLS[EUPDATESVN] SGX instruction
> is supported. This will be used by SGX driver to perform CPU
> SVN updates.
> 
> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>

Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>

[PATCH v10 4/6] x86/sgx: Define error codes for use by ENCLS[EUPDATESVN]

[Elena Reshetova]

Add error codes for ENCLS[EUPDATESVN], then SGX CPUSVN update
process can know the execution state of EUPDATESVN and notify
userspace.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 arch/x86/include/asm/sgx.h | 37 ++++++++++++++++++++++---------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
index 6a0069761508..1abf1461fab6 100644
--- a/arch/x86/include/asm/sgx.h
+++ b/arch/x86/include/asm/sgx.h
@@ -28,21 +28,22 @@
 #define SGX_CPUID_EPC_MASK	GENMASK(3, 0)
 
 enum sgx_encls_function {
-	ECREATE	= 0x00,
-	EADD	= 0x01,
-	EINIT	= 0x02,
-	EREMOVE	= 0x03,
-	EDGBRD	= 0x04,
-	EDGBWR	= 0x05,
-	EEXTEND	= 0x06,
-	ELDU	= 0x08,
-	EBLOCK	= 0x09,
-	EPA	= 0x0A,
-	EWB	= 0x0B,
-	ETRACK	= 0x0C,
-	EAUG	= 0x0D,
-	EMODPR	= 0x0E,
-	EMODT	= 0x0F,
+	ECREATE		= 0x00,
+	EADD		= 0x01,
+	EINIT		= 0x02,
+	EREMOVE		= 0x03,
+	EDGBRD		= 0x04,
+	EDGBWR		= 0x05,
+	EEXTEND		= 0x06,
+	ELDU		= 0x08,
+	EBLOCK		= 0x09,
+	EPA		= 0x0A,
+	EWB		= 0x0B,
+	ETRACK		= 0x0C,
+	EAUG		= 0x0D,
+	EMODPR		= 0x0E,
+	EMODT		= 0x0F,
+	EUPDATESVN	= 0x18,
 };
 
 /**
@@ -73,6 +74,10 @@ enum sgx_encls_function {
  *				public key does not match IA32_SGXLEPUBKEYHASH.
  * %SGX_PAGE_NOT_MODIFIABLE:	The EPC page cannot be modified because it
  *				is in the PENDING or MODIFIED state.
+ * %SGX_INSUFFICIENT_ENTROPY:	Insufficient entropy in RNG.
+ * %SGX_NO_UPDATE:		EUPDATESVN was successful, but CPUSVN was not
+ *				updated because current SVN was not newer than
+ *				CPUSVN.
  * %SGX_UNMASKED_EVENT:		An unmasked event, e.g. INTR, was received
  */
 enum sgx_return_code {
@@ -81,6 +86,8 @@ enum sgx_return_code {
 	SGX_CHILD_PRESENT		= 13,
 	SGX_INVALID_EINITTOKEN		= 16,
 	SGX_PAGE_NOT_MODIFIABLE		= 20,
+	SGX_INSUFFICIENT_ENTROPY	= 29,
+	SGX_NO_UPDATE				= 31,
 	SGX_UNMASKED_EVENT		= 128,
 };
 
-- 
2.45.2

Re: [PATCH v10 4/6] x86/sgx: Define error codes for use by ENCLS[EUPDATESVN]

[Dave Hansen]

On 8/1/25 04:25, Elena Reshetova wrote:
> Add error codes for ENCLS[EUPDATESVN], then SGX CPUSVN update
> process can know the execution state of EUPDATESVN and notify
> userspace.
> 
> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> ---
>  arch/x86/include/asm/sgx.h | 37 ++++++++++++++++++++++---------------
>  1 file changed, 22 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> index 6a0069761508..1abf1461fab6 100644
> --- a/arch/x86/include/asm/sgx.h
> +++ b/arch/x86/include/asm/sgx.h
> @@ -28,21 +28,22 @@
>  #define SGX_CPUID_EPC_MASK	GENMASK(3, 0)
>  
>  enum sgx_encls_function {
> -	ECREATE	= 0x00,
> -	EADD	= 0x01,
> -	EINIT	= 0x02,
> -	EREMOVE	= 0x03,
> -	EDGBRD	= 0x04,
> -	EDGBWR	= 0x05,
> -	EEXTEND	= 0x06,
> -	ELDU	= 0x08,
> -	EBLOCK	= 0x09,
> -	EPA	= 0x0A,
> -	EWB	= 0x0B,
> -	ETRACK	= 0x0C,
> -	EAUG	= 0x0D,
> -	EMODPR	= 0x0E,
> -	EMODT	= 0x0F,
> +	ECREATE		= 0x00,
> +	EADD		= 0x01,
> +	EINIT		= 0x02,
> +	EREMOVE		= 0x03,
> +	EDGBRD		= 0x04,
> +	EDGBWR		= 0x05,
> +	EEXTEND		= 0x06,
> +	ELDU		= 0x08,
> +	EBLOCK		= 0x09,
> +	EPA		= 0x0A,
> +	EWB		= 0x0B,
> +	ETRACK		= 0x0C,
> +	EAUG		= 0x0D,
> +	EMODPR		= 0x0E,
> +	EMODT		= 0x0F,
> +	EUPDATESVN	= 0x18,
>  };

This update is not consistent with the changelog nor the patch subject.

>  /**
> @@ -73,6 +74,10 @@ enum sgx_encls_function {
>   *				public key does not match IA32_SGXLEPUBKEYHASH.
>   * %SGX_PAGE_NOT_MODIFIABLE:	The EPC page cannot be modified because it
>   *				is in the PENDING or MODIFIED state.
> + * %SGX_INSUFFICIENT_ENTROPY:	Insufficient entropy in RNG.
> + * %SGX_NO_UPDATE:		EUPDATESVN was successful, but CPUSVN was not
> + *				updated because current SVN was not newer than
> + *				CPUSVN.

This comment bothers me. This is an *ERROR* code. It means that
EUPDATESVN was *NOT* successful. It failed. It didn't do an update.

Now, it's not a _bad_ error code. It's kinda like read() returning 0.
It's a "no harm no foul" kind of thing. But it's *NOT* success.

Ideally, we find a way to relay this in a very succinct way.

RE: [PATCH v10 4/6] x86/sgx: Define error codes for use by ENCLS[EUPDATESVN]

[Reshetova, Elena]

> -----Original Message-----
> From: Hansen, Dave <dave.hansen@intel.com>
> Sent: Friday, August 1, 2025 7:57 PM
> To: Reshetova, Elena <elena.reshetova@intel.com>
> Cc: jarkko@kernel.org; seanjc@google.com; Huang, Kai
> <kai.huang@intel.com>; mingo@kernel.org; linux-sgx@vger.kernel.org; linux-
> kernel@vger.kernel.org; x86@kernel.org; Mallick, Asit K
> <asit.k.mallick@intel.com>; Scarlata, Vincent R <vincent.r.scarlata@intel.com>;
> Cai, Chong <chongc@google.com>; Aktas, Erdem <erdemaktas@google.com>;
> Annapurve, Vishal <vannapurve@google.com>; Bondarevska, Nataliia
> <bondarn@google.com>; Raynor, Scott <scott.raynor@intel.com>
> Subject: Re: [PATCH v10 4/6] x86/sgx: Define error codes for use by
> ENCLS[EUPDATESVN]
> 
> On 8/1/25 04:25, Elena Reshetova wrote:
> > Add error codes for ENCLS[EUPDATESVN], then SGX CPUSVN update
> > process can know the execution state of EUPDATESVN and notify
> > userspace.
> >
> > Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> > ---
> >  arch/x86/include/asm/sgx.h | 37 ++++++++++++++++++++++---------------
> >  1 file changed, 22 insertions(+), 15 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> > index 6a0069761508..1abf1461fab6 100644
> > --- a/arch/x86/include/asm/sgx.h
> > +++ b/arch/x86/include/asm/sgx.h
> > @@ -28,21 +28,22 @@
> >  #define SGX_CPUID_EPC_MASK	GENMASK(3, 0)
> >
> >  enum sgx_encls_function {
> > -	ECREATE	= 0x00,
> > -	EADD	= 0x01,
> > -	EINIT	= 0x02,
> > -	EREMOVE	= 0x03,
> > -	EDGBRD	= 0x04,
> > -	EDGBWR	= 0x05,
> > -	EEXTEND	= 0x06,
> > -	ELDU	= 0x08,
> > -	EBLOCK	= 0x09,
> > -	EPA	= 0x0A,
> > -	EWB	= 0x0B,
> > -	ETRACK	= 0x0C,
> > -	EAUG	= 0x0D,
> > -	EMODPR	= 0x0E,
> > -	EMODT	= 0x0F,
> > +	ECREATE		= 0x00,
> > +	EADD		= 0x01,
> > +	EINIT		= 0x02,
> > +	EREMOVE		= 0x03,
> > +	EDGBRD		= 0x04,
> > +	EDGBWR		= 0x05,
> > +	EEXTEND		= 0x06,
> > +	ELDU		= 0x08,
> > +	EBLOCK		= 0x09,
> > +	EPA		= 0x0A,
> > +	EWB		= 0x0B,
> > +	ETRACK		= 0x0C,
> > +	EAUG		= 0x0D,
> > +	EMODPR		= 0x0E,
> > +	EMODT		= 0x0F,
> > +	EUPDATESVN	= 0x18,
> >  };
> 
> This update is not consistent with the changelog nor the patch subject.

I can remove the alignment fix.  

> 
> >  /**
> > @@ -73,6 +74,10 @@ enum sgx_encls_function {
> >   *				public key does not match
> IA32_SGXLEPUBKEYHASH.
> >   * %SGX_PAGE_NOT_MODIFIABLE:	The EPC page cannot be modified
> because it
> >   *				is in the PENDING or MODIFIED state.
> > + * %SGX_INSUFFICIENT_ENTROPY:	Insufficient entropy in RNG.
> > + * %SGX_NO_UPDATE:		EUPDATESVN was successful, but
> CPUSVN was not
> > + *				updated because current SVN was not newer
> than
> > + *				CPUSVN.
> 
> This comment bothers me. This is an *ERROR* code. It means that
> EUPDATESVN was *NOT* successful. It failed. It didn't do an update.
> 
> Now, it's not a _bad_ error code. It's kinda like read() returning 0.
> It's a "no harm no foul" kind of thing. But it's *NOT* success.

Yes, agree on both. 

> 
> Ideally, we find a way to relay this in a very succinct way.

Could you please elaborate what you mean by this? 
Changing the description? The name or? 

Best Regards,
Elena. 

Re: [PATCH v10 4/6] x86/sgx: Define error codes for use by ENCLS[EUPDATESVN]

[Dave Hansen]

On 8/4/25 00:21, Reshetova, Elena wrote:
...
>>> +	EUPDATESVN	= 0x18,
>>>  };
>>
>> This update is not consistent with the changelog nor the patch subject.
> 
> I can remove the alignment fix.  

It's not the alignment.

It's the definition of EUPDATESVN that goes completely unmentioned.

...
>> Ideally, we find a way to relay this in a very succinct way.
> 
> Could you please elaborate what you mean by this? 
> Changing the description? The name or? 

Relaying it in the comment next to the definition would be best.

RE: [PATCH v10 4/6] x86/sgx: Define error codes for use by ENCLS[EUPDATESVN]

[Reshetova, Elena]

> -----Original Message-----
> From: Hansen, Dave <dave.hansen@intel.com>
> Sent: Monday, August 4, 2025 5:20 PM
> To: Reshetova, Elena <elena.reshetova@intel.com>
> Cc: jarkko@kernel.org; seanjc@google.com; Huang, Kai
> <kai.huang@intel.com>; mingo@kernel.org; linux-sgx@vger.kernel.org; linux-
> kernel@vger.kernel.org; x86@kernel.org; Mallick, Asit K
> <asit.k.mallick@intel.com>; Scarlata, Vincent R <vincent.r.scarlata@intel.com>;
> Cai, Chong <chongc@google.com>; Aktas, Erdem <erdemaktas@google.com>;
> Annapurve, Vishal <vannapurve@google.com>; Bondarevska, Nataliia
> <bondarn@google.com>; Raynor, Scott <scott.raynor@intel.com>
> Subject: Re: [PATCH v10 4/6] x86/sgx: Define error codes for use by
> ENCLS[EUPDATESVN]
> 
> On 8/4/25 00:21, Reshetova, Elena wrote:
> ...
> >>> +	EUPDATESVN	= 0x18,
> >>>  };
> >>
> >> This update is not consistent with the changelog nor the patch subject.
> >
> > I can remove the alignment fix.
> 
> It's not the alignment.
> 
> It's the definition of EUPDATESVN that goes completely unmentioned.

Yes, good catch, this should be moved to the next patch indeed. 

> 
> ...
> >> Ideally, we find a way to relay this in a very succinct way.
> >
> > Could you please elaborate what you mean by this?
> > Changing the description? The name or?
> 
> Relaying it in the comment next to the definition would be best.

Sure, will try to extend the current description to convey it better.

Best Regards,
Elena. 

[PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN]

[Elena Reshetova]

All running enclaves and cryptographic assets (such as internal SGX
encryption keys) are assumed to be compromised whenever an SGX-related
microcode update occurs. To mitigate this assumed compromise the new
supervisor SGX instruction ENCLS[EUPDATESVN] can generate fresh
cryptographic assets.

Before executing EUPDATESVN, all SGX memory must be marked as unused.
This requirement ensures that no potentially compromised enclave
survives the update and allows the system to safely regenerate
cryptographic assets.

Add the method to perform ENCLS[EUPDATESVN].

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 arch/x86/kernel/cpu/sgx/encls.h |  5 +++
 arch/x86/kernel/cpu/sgx/main.c  | 61 +++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
index 99004b02e2ed..d9160c89a93d 100644
--- a/arch/x86/kernel/cpu/sgx/encls.h
+++ b/arch/x86/kernel/cpu/sgx/encls.h
@@ -233,4 +233,9 @@ static inline int __eaug(struct sgx_pageinfo *pginfo, void *addr)
 	return __encls_2(EAUG, pginfo, addr);
 }
 
+/* Attempt to update CPUSVN at runtime. */
+static inline int __eupdatesvn(void)
+{
+	return __encls_ret_1(EUPDATESVN, "");
+}
 #endif /* _X86_ENCLS_H */
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 3a5cbd1c170e..5aae0c881963 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -16,6 +16,7 @@
 #include <linux/vmalloc.h>
 #include <asm/msr.h>
 #include <asm/sgx.h>
+#include <asm/archrandom.h>
 #include "driver.h"
 #include "encl.h"
 #include "encls.h"
@@ -917,6 +918,66 @@ int sgx_set_attribute(unsigned long *allowed_attributes,
 }
 EXPORT_SYMBOL_GPL(sgx_set_attribute);
 
+/**
+ * sgx_update_svn() - Attempt to call ENCLS[EUPDATESVN].
+ * This instruction attempts to update CPUSVN to the
+ * currently loaded microcode update SVN and generate new
+ * cryptographic assets. Must be called when EPC is empty.
+ * Most of the time, there will be no update and that's OK.
+ * If the failure is due to SGX_INSUFFICIENT_ENTROPY, the
+ * operation can be safely retried. In other failure cases,
+ * the retry should not be attempted.
+ *
+ * Return:
+ * 0: Success or not supported
+ * -EAGAIN: Can be safely retried, failure is due to lack of
+ *  entropy in RNG.
+ * -EIO: Unexpected error, retries are not advisable.
+ */
+static int __maybe_unused sgx_update_svn(void)
+{
+	int ret;
+
+	/*
+	 * If EUPDATESVN is not available, it is ok to
+	 * silently skip it to comply with legacy behavior.
+	 */
+	if (!cpu_feature_enabled(X86_FEATURE_SGX_EUPDATESVN))
+		return 0;
+
+	for (int i = 0; i < RDRAND_RETRY_LOOPS; i++) {
+		ret = __eupdatesvn();
+
+		/* Stop on success or unexpected errors: */
+		if (ret != SGX_INSUFFICIENT_ENTROPY)
+			break;
+	}
+
+	/*
+	 * SVN successfully updated.
+	 * Let users know when the update was successful.
+	 */
+	if (!ret)
+		pr_info("SVN updated successfully\n");
+
+	if (!ret || ret == SGX_NO_UPDATE)
+		return 0;
+
+	/*
+	 * SVN update failed due to lack of entropy in DRNG.
+	 * Indicate to userspace that it should retry.
+	 */
+	if (ret == SGX_INSUFFICIENT_ENTROPY)
+		return -EAGAIN;
+
+	/*
+	 * EUPDATESVN was called when EPC is empty, all other error
+	 * codes are unexpected.
+	 */
+	ENCLS_WARN(ret, "EUPDATESVN");
+	return -EIO;
+}
+
 int sgx_inc_usage_count(void)
 {
 	return 0;
-- 
2.45.2

Re: [PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN]

[Dave Hansen]

The changelog is missing a tidbit about the fact that this is still dead
code until sgx_inc_usage_count() gets a real implementation.

On 8/1/25 04:25, Elena Reshetova wrote:
...
> +/**
> + * sgx_update_svn() - Attempt to call ENCLS[EUPDATESVN].
> + * This instruction attempts to update CPUSVN to the
> + * currently loaded microcode update SVN and generate new
> + * cryptographic assets. Must be called when EPC is empty.

As a general rule, I'd much rather have the "Must be $FOO" rules written
in code than in a comment, or along with a comment:

	/* EPC is guaranteed to be empty when there are no users: */
	WARN(count, "Elevated usage count...");

> + * Most of the time, there will be no update and that's OK.

This should go with the check for SGX_NO_UPDATE, not here.

> + * If the failure is due to SGX_INSUFFICIENT_ENTROPY, the
> + * operation can be safely retried. In other failure cases,
> + * the retry should not be attempted.

Ditto. This is rewriting the code in comments.

> + * Return:
> + * 0: Success or not supported
> + * -EAGAIN: Can be safely retried, failure is due to lack of
> + *  entropy in RNG.
> + * -EIO: Unexpected error, retries are not advisable.
> + */
> +static int __maybe_unused sgx_update_svn(void)
> +{
> +	int ret;
> +
> +	/*
> +	 * If EUPDATESVN is not available, it is ok to
> +	 * silently skip it to comply with legacy behavior.
> +	 */
> +	if (!cpu_feature_enabled(X86_FEATURE_SGX_EUPDATESVN))
> +		return 0;
> +
> +	for (int i = 0; i < RDRAND_RETRY_LOOPS; i++) {
> +		ret = __eupdatesvn();
> +
> +		/* Stop on success or unexpected errors: */
> +		if (ret != SGX_INSUFFICIENT_ENTROPY)
> +			break;
> +	}
> +
> +	/*
> +	 * SVN successfully updated.
> +	 * Let users know when the update was successful.
> +	 */
> +	if (!ret)
> +		pr_info("SVN updated successfully\n");
> +
> +	if (!ret || ret == SGX_NO_UPDATE)
> +		return 0;
> +
> +	/*
> +	 * SVN update failed due to lack of entropy in DRNG.
> +	 * Indicate to userspace that it should retry.
> +	 */
> +	if (ret == SGX_INSUFFICIENT_ENTROPY)
> +		return -EAGAIN;

There are four cases to handle. Doesn't it make sense to just write it
as four literal "case"s?

	switch (ret) {
	case 0:
		pr_info("...");
		return 0;
	case SGX_NO_UPDATE:
		return 0;
	case SGX_INSUFFICIENT_ENTROPY:
		return -EAGAIN;
	default:
		break;
	}


> +	ENCLS_WARN(ret, "EUPDATESVN");
> +	return -EIO;
> +}
> +
>  int sgx_inc_usage_count(void)
>  {
>  	return 0;

RE: [PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN]

[Reshetova, Elena]

> -----Original Message-----
> From: Hansen, Dave <dave.hansen@intel.com>
> Sent: Friday, August 1, 2025 8:13 PM
> To: Reshetova, Elena <elena.reshetova@intel.com>
> Cc: jarkko@kernel.org; seanjc@google.com; Huang, Kai
> <kai.huang@intel.com>; mingo@kernel.org; linux-sgx@vger.kernel.org; linux-
> kernel@vger.kernel.org; x86@kernel.org; Mallick, Asit K
> <asit.k.mallick@intel.com>; Scarlata, Vincent R <vincent.r.scarlata@intel.com>;
> Cai, Chong <chongc@google.com>; Aktas, Erdem <erdemaktas@google.com>;
> Annapurve, Vishal <vannapurve@google.com>; Bondarevska, Nataliia
> <bondarn@google.com>; Raynor, Scott <scott.raynor@intel.com>
> Subject: Re: [PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN]
> 
> The changelog is missing a tidbit about the fact that this is still dead
> code until sgx_inc_usage_count() gets a real implementation.

Will add. 

> 
> On 8/1/25 04:25, Elena Reshetova wrote:
> ...
> > +/**
> > + * sgx_update_svn() - Attempt to call ENCLS[EUPDATESVN].
> > + * This instruction attempts to update CPUSVN to the
> > + * currently loaded microcode update SVN and generate new
> > + * cryptographic assets. Must be called when EPC is empty.
> 
> As a general rule, I'd much rather have the "Must be $FOO" rules written
> in code than in a comment, or along with a comment:
> 
> 	/* EPC is guaranteed to be empty when there are no users: */
> 	WARN(count, "Elevated usage count...");

I will change to do it this way. 

> 
> > + * Most of the time, there will be no update and that's OK.
> 
> This should go with the check for SGX_NO_UPDATE, not here.

Ok, will fix. 

> 
> > + * If the failure is due to SGX_INSUFFICIENT_ENTROPY, the
> > + * operation can be safely retried. In other failure cases,
> > + * the retry should not be attempted.
> 
> Ditto. This is rewriting the code in comments.

Ok, will drop. 

> 
> > + * Return:
> > + * 0: Success or not supported
> > + * -EAGAIN: Can be safely retried, failure is due to lack of
> > + *  entropy in RNG.
> > + * -EIO: Unexpected error, retries are not advisable.
> > + */
> > +static int __maybe_unused sgx_update_svn(void)
> > +{
> > +	int ret;
> > +
> > +	/*
> > +	 * If EUPDATESVN is not available, it is ok to
> > +	 * silently skip it to comply with legacy behavior.
> > +	 */
> > +	if (!cpu_feature_enabled(X86_FEATURE_SGX_EUPDATESVN))
> > +		return 0;
> > +
> > +	for (int i = 0; i < RDRAND_RETRY_LOOPS; i++) {
> > +		ret = __eupdatesvn();
> > +
> > +		/* Stop on success or unexpected errors: */
> > +		if (ret != SGX_INSUFFICIENT_ENTROPY)
> > +			break;
> > +	}
> > +
> > +	/*
> > +	 * SVN successfully updated.
> > +	 * Let users know when the update was successful.
> > +	 */
> > +	if (!ret)
> > +		pr_info("SVN updated successfully\n");
> > +
> > +	if (!ret || ret == SGX_NO_UPDATE)
> > +		return 0;
> > +
> > +	/*
> > +	 * SVN update failed due to lack of entropy in DRNG.
> > +	 * Indicate to userspace that it should retry.
> > +	 */
> > +	if (ret == SGX_INSUFFICIENT_ENTROPY)
> > +		return -EAGAIN;
> 
> There are four cases to handle. Doesn't it make sense to just write it
> as four literal "case"s?
> 
> 	switch (ret) {
> 	case 0:
> 		pr_info("...");
> 		return 0;
> 	case SGX_NO_UPDATE:
> 		return 0;
> 	case SGX_INSUFFICIENT_ENTROPY:
> 		return -EAGAIN;
> 	default:
> 		break;
> 	}
> 
> 

Will re-write accordingly. 

Thank you very much  for your prompt review Dave!

Best Regards,
Elena.

[PATCH v10 6/6] x86/sgx: Enable automatic SVN updates for SGX enclaves

[Elena Reshetova]

== Background ==

ENCLS[EUPDATESVN] is a new SGX instruction [1] which allows enclave
attestation to include information about updated microcode SVN without a
reboot. Before an EUPDATESVN operation can be successful, all SGX memory
(aka. EPC) must be marked as “unused” in the SGX hardware metadata
(aka.EPCM). This requirement ensures that no compromised enclave can
survive the EUPDATESVN procedure and provides an opportunity to generate
new cryptographic assets.

== Solution ==

Attempt to execute ENCLS[EUPDATESVN] every time the first file descriptor
is obtained via sgx_(vepc_)open(). In the most common case the microcode
SVN is already up-to-date, and the operation succeeds without updating SVN.
Note: while in such cases the underlying CR_BASE_KEY is regenrated, it does
not affect enclaves' visible keys obtained via EGETKEY instruction.

If it fails with any other error code than SGX_INSUFFICIENT_ENTROPY, this
is considered unexpected and the *open() returns an error. This should not
happen in practice.

On contrary, SGX_INSUFFICIENT_ENTROPY might happen due
to a pressure on the system's DRNG (RDSEED) and therefore the *open() can
be safely retried to allow normal enclave operation.

[1] Runtime Microcode Updates with Intel Software Guard Extensions,
https://cdrdv2.intel.com/v1/dl/getContent/648682

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 arch/x86/kernel/cpu/sgx/main.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 5aae0c881963..6a5d5cd726f6 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -934,7 +934,7 @@ EXPORT_SYMBOL_GPL(sgx_set_attribute);
  *  entropy in RNG.
  * -EIO: Unexpected error, retries are not advisable.
  */
-static int __maybe_unused sgx_update_svn(void)
+static int sgx_update_svn(void)
 {
 	int ret;
 
@@ -978,14 +978,25 @@ static int __maybe_unused sgx_update_svn(void)
 	return -EIO;
 }
 
+/* Counter to count the active SGX users */
+static int sgx_usage_count;
+
+/* Mutex to ensure no concurrent EPC accesses during EUPDATESVN */
+static DEFINE_MUTEX(sgx_svn_lock);
+
 int sgx_inc_usage_count(void)
 {
+	guard(mutex)(&sgx_svn_lock);
+
+	if (sgx_usage_count++ == 0)
+		return sgx_update_svn();
+
 	return 0;
 }
 
 void sgx_dec_usage_count(void)
 {
-	return;
+	sgx_usage_count--;
 }
 
 static int __init sgx_init(void)
-- 
2.45.2