[patch V2 0/2] sysfs/cpu: Implement generic vulnerabilites directory

[patch V2 0/2] sysfs/cpu: Implement generic vulnerabilites directory

[Thomas Gleixner]

The meltdown/spectre vulnerabilities affect several architectures and
people are asking for a common way to figure out whether a system is
affected or not.

Create

   /sys/devices/system/cpu/vulnerabilites

and the files

   /sys/devices/system/cpu/vulnerabilites/meltdown
   /sys/devices/system/cpu/vulnerabilites/spectre_v1
   /sys/devices/system/cpu/vulnerabilites/spectre_v2

Add the x86 implementation which shows:

meltdown    Mitigation: PTI
spectre_v1  Vulnerable
sepctre_v1  Vulnerable
   
On an AMD CPU the output of meltdown is: Not affected.

If PTI is turned off and the CPU is affected of meltdown the output
becomes: Vulnerable

That series applies on top of

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/pti

V1 -> V2: Add documentation and use sprintf

Thanks,

	tglx

[patch V2 1/2] sysfs/cpu: Add vulnerability folder

[Thomas Gleixner]

[-- Attachment #1: sysfs-cpu--Add-vulnerability-folder.patch --]
[-- Type: text/plain, Size: 4334 bytes --]

As the meltdown/spectre problem affects several CPU architectures, it makes
sense to have common way to express whether a system is affected by a
particular vulnerability or not. If affected the way to express the
mitigation should be common as well.

Create /sys/devices/system/cpu/vulnerabilities folder and files for
meltdown, spectre_v1 and spectre_v2.

Allow architectures to override the show function.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 Documentation/ABI/testing/sysfs-devices-system-cpu |   16 +++++++
 drivers/base/Kconfig                               |    3 +
 drivers/base/cpu.c                                 |   48 +++++++++++++++++++++
 include/linux/cpu.h                                |    7 +++
 4 files changed, 74 insertions(+)

--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -373,3 +373,19 @@ Contact:	Linux kernel mailing list <linu
 Description:	information about CPUs heterogeneity.
 
 		cpu_capacity: capacity of cpu#.
+
+What:		/sys/devices/system/cpu/vulnerabilities
+		/sys/devices/system/cpu/vulnerabilities/meltdown
+		/sys/devices/system/cpu/vulnerabilities/spectre_v1
+		/sys/devices/system/cpu/vulnerabilities/spectre_v2
+Date:		Januar 2018
+Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description:	Information about CPU vulnerabilities
+
+		The files are named after the code names of CPU
+		vulnerabilities. The output of those files reflects the
+		state of the CPUs in the system. Possible output values:
+
+		"Not affected"	  CPU is not affected by the vulnerability
+		"Vulnerable"	  CPU is affected and no mitigation in effect
+		"Mitigation: $M"  CPU is affetcted and mitigation $M is in effect
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -235,6 +235,9 @@ config GENERIC_CPU_DEVICES
 config GENERIC_CPU_AUTOPROBE
 	bool
 
+config GENERIC_CPU_VULNERABILITIES
+	bool
+
 config SOC_BUS
 	bool
 	select GLOB
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -501,10 +501,58 @@ static void __init cpu_dev_register_gene
 #endif
 }
 
+#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES
+
+ssize_t __weak cpu_show_meltdown(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "Not affected\n");
+}
+
+ssize_t __weak cpu_show_spectre_v1(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "Not affected\n");
+}
+
+ssize_t __weak cpu_show_spectre_v2(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "Not affected\n");
+}
+
+static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
+static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
+static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
+
+static struct attribute *cpu_root_vulnerabilities_attrs[] = {
+	&dev_attr_meltdown.attr,
+	&dev_attr_spectre_v1.attr,
+	&dev_attr_spectre_v2.attr,
+	NULL
+};
+
+static const struct attribute_group cpu_root_vulnerabilities_group = {
+	.name  = "vulnerabilities",
+	.attrs = cpu_root_vulnerabilities_attrs,
+};
+
+static void __init cpu_register_vulnerabilities(void)
+{
+	if (sysfs_create_group(&cpu_subsys.dev_root->kobj,
+			       &cpu_root_vulnerabilities_group))
+		pr_err("Unable to register CPU vulnerabilities\n");
+}
+
+#else
+static inline void cpu_register_vulnerabilities(void) { }
+#endif
+
 void __init cpu_dev_init(void)
 {
 	if (subsys_system_register(&cpu_subsys, cpu_root_attr_groups))
 		panic("Failed to register CPU subsystem");
 
 	cpu_dev_register_generic();
+	cpu_register_vulnerabilities();
 }
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -47,6 +47,13 @@ extern void cpu_remove_dev_attr(struct d
 extern int cpu_add_dev_attr_group(struct attribute_group *attrs);
 extern void cpu_remove_dev_attr_group(struct attribute_group *attrs);
 
+extern ssize_t cpu_show_meltdown(struct device *dev,
+				 struct device_attribute *attr, char *buf);
+extern ssize_t cpu_show_spectre_v1(struct device *dev,
+				   struct device_attribute *attr, char *buf);
+extern ssize_t cpu_show_spectre_v2(struct device *dev,
+				   struct device_attribute *attr, char *buf);
+
 extern __printf(4, 5)
 struct device *cpu_device_create(struct device *parent, void *drvdata,
 				 const struct attribute_group **groups,

Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

[Konrad Rzeszutek Wilk]

On Sun, Jan 07, 2018 at 10:48:00PM +0100, Thomas Gleixner wrote:
> As the meltdown/spectre problem affects several CPU architectures, it makes
> sense to have common way to express whether a system is affected by a
> particular vulnerability or not. If affected the way to express the
> mitigation should be common as well.
> 
> Create /sys/devices/system/cpu/vulnerabilities folder and files for
> meltdown, spectre_v1 and spectre_v2.
> 
> Allow architectures to override the show function.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  Documentation/ABI/testing/sysfs-devices-system-cpu |   16 +++++++
>  drivers/base/Kconfig                               |    3 +
>  drivers/base/cpu.c                                 |   48 +++++++++++++++++++++
>  include/linux/cpu.h                                |    7 +++
>  4 files changed, 74 insertions(+)
> 
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -373,3 +373,19 @@ Contact:	Linux kernel mailing list <linu
>  Description:	information about CPUs heterogeneity.
>  
>  		cpu_capacity: capacity of cpu#.
> +
> +What:		/sys/devices/system/cpu/vulnerabilities
> +		/sys/devices/system/cpu/vulnerabilities/meltdown
> +		/sys/devices/system/cpu/vulnerabilities/spectre_v1
> +		/sys/devices/system/cpu/vulnerabilities/spectre_v2
> +Date:		Januar 2018

s/Januar/January/

and with that
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Thank you!
> +#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES
> +
> +ssize_t __weak cpu_show_meltdown(struct device *dev,
> +				 struct device_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "Not affected\n");
> +}
> +
> +ssize_t __weak cpu_show_spectre_v1(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "Not affected\n");
> +}
> +
> +ssize_t __weak cpu_show_spectre_v2(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "Not affected\n");
> +}
> +
> +static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
> +static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
> +static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
> +
> +static struct attribute *cpu_root_vulnerabilities_attrs[] = {
> +	&dev_attr_meltdown.attr,
> +	&dev_attr_spectre_v1.attr,
> +	&dev_attr_spectre_v2.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group cpu_root_vulnerabilities_group = {
> +	.name  = "vulnerabilities",
> +	.attrs = cpu_root_vulnerabilities_attrs,
> +};
> +
> +static void __init cpu_register_vulnerabilities(void)
> +{
> +	if (sysfs_create_group(&cpu_subsys.dev_root->kobj,
> +			       &cpu_root_vulnerabilities_group))
> +		pr_err("Unable to register CPU vulnerabilities\n");
> +}
> +
> +#else
> +static inline void cpu_register_vulnerabilities(void) { }
> +#endif
> +
>  void __init cpu_dev_init(void)
>  {
>  	if (subsys_system_register(&cpu_subsys, cpu_root_attr_groups))
>  		panic("Failed to register CPU subsystem");
>  
>  	cpu_dev_register_generic();
> +	cpu_register_vulnerabilities();
>  }
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -47,6 +47,13 @@ extern void cpu_remove_dev_attr(struct d
>  extern int cpu_add_dev_attr_group(struct attribute_group *attrs);
>  extern void cpu_remove_dev_attr_group(struct attribute_group *attrs);
>  
> +extern ssize_t cpu_show_meltdown(struct device *dev,
> +				 struct device_attribute *attr, char *buf);
> +extern ssize_t cpu_show_spectre_v1(struct device *dev,
> +				   struct device_attribute *attr, char *buf);
> +extern ssize_t cpu_show_spectre_v2(struct device *dev,
> +				   struct device_attribute *attr, char *buf);
> +
>  extern __printf(4, 5)
>  struct device *cpu_device_create(struct device *parent, void *drvdata,
>  				 const struct attribute_group **groups,
> 
> 

Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

[Greg Kroah-Hartman]

On Sun, Jan 07, 2018 at 10:48:00PM +0100, Thomas Gleixner wrote:
> As the meltdown/spectre problem affects several CPU architectures, it makes
> sense to have common way to express whether a system is affected by a
> particular vulnerability or not. If affected the way to express the
> mitigation should be common as well.
> 
> Create /sys/devices/system/cpu/vulnerabilities folder and files for
> meltdown, spectre_v1 and spectre_v2.
> 
> Allow architectures to override the show function.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Thanks for the documentation update, looks good to me:

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

[Dominik Brodowski]

On Sun, Jan 07, 2018 at 10:48:00PM +0100, Thomas Gleixner wrote:
> As the meltdown/spectre problem affects several CPU architectures, it makes
> sense to have common way to express whether a system is affected by a
> particular vulnerability or not. If affected the way to express the
> mitigation should be common as well.
> 
> Create /sys/devices/system/cpu/vulnerabilities folder and files for
> meltdown, spectre_v1 and spectre_v2.
> 
> Allow architectures to override the show function.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  Documentation/ABI/testing/sysfs-devices-system-cpu |   16 +++++++
>  drivers/base/Kconfig                               |    3 +
>  drivers/base/cpu.c                                 |   48 +++++++++++++++++++++
>  include/linux/cpu.h                                |    7 +++
>  4 files changed, 74 insertions(+)
> 
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -373,3 +373,19 @@ Contact:	Linux kernel mailing list <linu
>  Description:	information about CPUs heterogeneity.
>  
>  		cpu_capacity: capacity of cpu#.
> +
> +What:		/sys/devices/system/cpu/vulnerabilities
> +		/sys/devices/system/cpu/vulnerabilities/meltdown
> +		/sys/devices/system/cpu/vulnerabilities/spectre_v1
> +		/sys/devices/system/cpu/vulnerabilities/spectre_v2
> +Date:		Januar 2018
> +Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> +Description:	Information about CPU vulnerabilities
> +
> +		The files are named after the code names of CPU
> +		vulnerabilities. The output of those files reflects the
> +		state of the CPUs in the system.

Currently, your code sets X86_BUG_SPECTRE_V[12] unconditionally on x86
CPUs. However, to my understanding some CPUs which do not execute code
out-of-order aren't affected. As it is better to err on the safe side for
now, what about adding a disclaimer at the end of this sentence, such as:

	", but may contain false positives"

Thanks,
	Dominik

Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

[Thomas Gleixner]

On Mon, 8 Jan 2018, Dominik Brodowski wrote:
> On Sun, Jan 07, 2018 at 10:48:00PM +0100, Thomas Gleixner wrote:
> > As the meltdown/spectre problem affects several CPU architectures, it makes
> > sense to have common way to express whether a system is affected by a
> > particular vulnerability or not. If affected the way to express the
> > mitigation should be common as well.
> > 
> > Create /sys/devices/system/cpu/vulnerabilities folder and files for
> > meltdown, spectre_v1 and spectre_v2.
> > 
> > Allow architectures to override the show function.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > ---
> >  Documentation/ABI/testing/sysfs-devices-system-cpu |   16 +++++++
> >  drivers/base/Kconfig                               |    3 +
> >  drivers/base/cpu.c                                 |   48 +++++++++++++++++++++
> >  include/linux/cpu.h                                |    7 +++
> >  4 files changed, 74 insertions(+)
> > 
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -373,3 +373,19 @@ Contact:	Linux kernel mailing list <linu
> >  Description:	information about CPUs heterogeneity.
> >  
> >  		cpu_capacity: capacity of cpu#.
> > +
> > +What:		/sys/devices/system/cpu/vulnerabilities
> > +		/sys/devices/system/cpu/vulnerabilities/meltdown
> > +		/sys/devices/system/cpu/vulnerabilities/spectre_v1
> > +		/sys/devices/system/cpu/vulnerabilities/spectre_v2
> > +Date:		Januar 2018
> > +Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
> > +Description:	Information about CPU vulnerabilities
> > +
> > +		The files are named after the code names of CPU
> > +		vulnerabilities. The output of those files reflects the
> > +		state of the CPUs in the system.
> 
> Currently, your code sets X86_BUG_SPECTRE_V[12] unconditionally on x86
> CPUs. However, to my understanding some CPUs which do not execute code
> out-of-order aren't affected. As it is better to err on the safe side for
> now, what about adding a disclaimer at the end of this sentence, such as:
> 
> 	", but may contain false positives"

We do that in the same way as we did with BUG_INSECURE (now MELTDOWN). Err
out on the safe side and get the exceptions in place when people are
confident about them. It's not going to take long I assume.

Thanks,

	tglx

[tip:x86/pti] sysfs/cpu: Add vulnerability folder

[tip-bot for Thomas Gleixner]

Commit-ID:  87590ce6e373d1a5401f6539f0c59ef92dd924a9
Gitweb:     https://git.kernel.org/tip/87590ce6e373d1a5401f6539f0c59ef92dd924a9
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Sun, 7 Jan 2018 22:48:00 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Mon, 8 Jan 2018 11:10:33 +0100

sysfs/cpu: Add vulnerability folder

As the meltdown/spectre problem affects several CPU architectures, it makes
sense to have common way to express whether a system is affected by a
particular vulnerability or not. If affected the way to express the
mitigation should be common as well.

Create /sys/devices/system/cpu/vulnerabilities folder and files for
meltdown, spectre_v1 and spectre_v2.

Allow architectures to override the show function.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lkml.kernel.org/r/20180107214913.096657732@linutronix.de

---
 Documentation/ABI/testing/sysfs-devices-system-cpu | 16 ++++++++
 drivers/base/Kconfig                               |  3 ++
 drivers/base/cpu.c                                 | 48 ++++++++++++++++++++++
 include/linux/cpu.h                                |  7 ++++
 4 files changed, 74 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index f3d5817..bd3a88e 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -373,3 +373,19 @@ Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
 Description:	information about CPUs heterogeneity.
 
 		cpu_capacity: capacity of cpu#.
+
+What:		/sys/devices/system/cpu/vulnerabilities
+		/sys/devices/system/cpu/vulnerabilities/meltdown
+		/sys/devices/system/cpu/vulnerabilities/spectre_v1
+		/sys/devices/system/cpu/vulnerabilities/spectre_v2
+Date:		Januar 2018
+Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description:	Information about CPU vulnerabilities
+
+		The files are named after the code names of CPU
+		vulnerabilities. The output of those files reflects the
+		state of the CPUs in the system. Possible output values:
+
+		"Not affected"	  CPU is not affected by the vulnerability
+		"Vulnerable"	  CPU is affected and no mitigation in effect
+		"Mitigation: $M"  CPU is affetcted and mitigation $M is in effect
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 2f6614c..37a71fd 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -235,6 +235,9 @@ config GENERIC_CPU_DEVICES
 config GENERIC_CPU_AUTOPROBE
 	bool
 
+config GENERIC_CPU_VULNERABILITIES
+	bool
+
 config SOC_BUS
 	bool
 	select GLOB
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 321cd7b..825964e 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -501,10 +501,58 @@ static void __init cpu_dev_register_generic(void)
 #endif
 }
 
+#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES
+
+ssize_t __weak cpu_show_meltdown(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "Not affected\n");
+}
+
+ssize_t __weak cpu_show_spectre_v1(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "Not affected\n");
+}
+
+ssize_t __weak cpu_show_spectre_v2(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "Not affected\n");
+}
+
+static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
+static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
+static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
+
+static struct attribute *cpu_root_vulnerabilities_attrs[] = {
+	&dev_attr_meltdown.attr,
+	&dev_attr_spectre_v1.attr,
+	&dev_attr_spectre_v2.attr,
+	NULL
+};
+
+static const struct attribute_group cpu_root_vulnerabilities_group = {
+	.name  = "vulnerabilities",
+	.attrs = cpu_root_vulnerabilities_attrs,
+};
+
+static void __init cpu_register_vulnerabilities(void)
+{
+	if (sysfs_create_group(&cpu_subsys.dev_root->kobj,
+			       &cpu_root_vulnerabilities_group))
+		pr_err("Unable to register CPU vulnerabilities\n");
+}
+
+#else
+static inline void cpu_register_vulnerabilities(void) { }
+#endif
+
 void __init cpu_dev_init(void)
 {
 	if (subsys_system_register(&cpu_subsys, cpu_root_attr_groups))
 		panic("Failed to register CPU subsystem");
 
 	cpu_dev_register_generic();
+	cpu_register_vulnerabilities();
 }
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 938ea8a..c816e6f 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -47,6 +47,13 @@ extern void cpu_remove_dev_attr(struct device_attribute *attr);
 extern int cpu_add_dev_attr_group(struct attribute_group *attrs);
 extern void cpu_remove_dev_attr_group(struct attribute_group *attrs);
 
+extern ssize_t cpu_show_meltdown(struct device *dev,
+				 struct device_attribute *attr, char *buf);
+extern ssize_t cpu_show_spectre_v1(struct device *dev,
+				   struct device_attribute *attr, char *buf);
+extern ssize_t cpu_show_spectre_v2(struct device *dev,
+				   struct device_attribute *attr, char *buf);
+
 extern __printf(4, 5)
 struct device *cpu_device_create(struct device *parent, void *drvdata,
 				 const struct attribute_group **groups,

Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

[Andrea Arcangeli]

Hello,

On Sun, Jan 07, 2018 at 10:48:00PM +0100, Thomas Gleixner wrote:
> +static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
> +static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
> +static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);

This sysfs feature implemented as above is weakening kernel security,
it should be 0400 above.

It doesn't make sense to expose to luser when a software fix (or even
only a software mitigation) has been disabled at build time to gain
all performance back (see CONFIG_RETPOLINE=n config option).

$ cat /boot/kernel-`uname -r`
cat: /boot/kernel-4.15.0-rc9+: Permission denied
$ cat /lib/modules/`uname -r`/kernel/arch/x86/kvm/kvm.ko 
cat: /lib/modules/4.15.0-rc9+/kernel/arch/x86/kvm/kvm.ko: Permission denied
$ dmesg
dmesg: read kernel buffer failed: Operation not permitted

Noticing when cr3 is flipped in kernel/exit is easy, but noticing when
the syscall table or the whole kernel has been built with retpolines
is not trivial to detect. Same for variant#1.

Exploiting spectre variant#2 for an attacker is not without risk of
being detected while the setup is being mounted, as the CPU load would
spike for hours.

I may notice if a random background network daemon suddenly starts
running at 100% CPU load for hours (especially on mobile devices that
would be physically noticeable).

Containers shouldn't have sysfs and you can workaround the above if
you run all network daemons behind mount namespaces, but in general
leaving this directory readable by luser is weaking security because
it exposes when mounting a variant#2 attack can succeed.

It even tells when it is worth to focus on the syscall_table indirect
call or if the attack needs to dig deeper because asm retpolines were
used, but the kernel was built with a gcc without retpolines.

The only case where the above isn't weakening security is when the
full fix is on for all the variants is enabled (and variant#1 for now
just shows vulnerable..).

For the same reasons the whole directory, not just the files, should be
0500, especially if this would be used for any other equivalent issue
in the future and it won't stick to these 3 files, I didn't implement
that yet, because it's less urgent if nobody adds any more files soon.

>From 578b411c8dcb1435dd1f94a6cd062f4eedb70fb5 Mon Sep 17 00:00:00 2001
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Wed, 24 Jan 2018 19:19:36 +0100
Subject: [PATCH 1/1] x86/spectre/meltdown: avoid the vulnerability directory
 to weaken kernel security

If any of the fixes is disabled to gain some performance back at
runtime or build time, should not be exposed to unprivileged userland.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
 drivers/base/cpu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index d99038487a0d..a3a8e008f957 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -531,9 +531,9 @@ ssize_t __weak cpu_show_spectre_v2(struct device *dev,
 	return sprintf(buf, "Not affected\n");
 }
 
-static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
-static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
-static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
+static DEVICE_ATTR(meltdown, 0400, cpu_show_meltdown, NULL);
+static DEVICE_ATTR(spectre_v1, 0400, cpu_show_spectre_v1, NULL);
+static DEVICE_ATTR(spectre_v2, 0400, cpu_show_spectre_v2, NULL);
 
 static struct attribute *cpu_root_vulnerabilities_attrs[] = {
 	&dev_attr_meltdown.attr,

Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

[Greg Kroah-Hartman]

On Fri, Jan 26, 2018 at 05:23:31PM +0100, Andrea Arcangeli wrote:
> Hello,
> 
> On Sun, Jan 07, 2018 at 10:48:00PM +0100, Thomas Gleixner wrote:
> > +static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
> > +static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
> > +static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
> 
> This sysfs feature implemented as above is weakening kernel security,
> it should be 0400 above.

See the patch from Jason A. Donenfeld <Jason@zx2c4.com> to do just that:
	Subject: [PATCH] cpu: do not leak vulnerabilities to unprivileged users
	Message-Id: <20180125120401.30596-1-Jason@zx2c4.com>

I'll be queueing it up for 4.16-rc1 and backport it everywhere.

thanks,

greg k-h

Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

[Jon Masters]

On 01/07/2018 04:48 PM, Thomas Gleixner wrote:

> +#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES
> +
> +ssize_t __weak cpu_show_meltdown(struct device *dev,
> +				 struct device_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "Not affected\n");
> +}
> +
> +ssize_t __weak cpu_show_spectre_v1(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "Not affected\n");
> +}
> +
> +ssize_t __weak cpu_show_spectre_v2(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "Not affected\n");
> +}

Just wondering aloud (after the merge) here but shouldn't the default be
"unknown", at least for Spectre? It's pervasive enough.

Jon.

[patch V2 2/2] x86/cpu: Implement CPU vulnerabilites sysfs functions

[Thomas Gleixner]

[-- Attachment #1: x86-cpu--Implement-CPU-vulnerabilites-sysfs-functions.patch --]
[-- Type: text/plain, Size: 1743 bytes --]

Implement the CPU vulnerabilty show functions for meltdown, spectre_v1 and
spectre_v2.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/Kconfig           |    1 +
 arch/x86/kernel/cpu/bugs.c |   29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -89,6 +89,7 @@ config X86
 	select GENERIC_CLOCKEVENTS_MIN_ADJUST
 	select GENERIC_CMOS_UPDATE
 	select GENERIC_CPU_AUTOPROBE
+	select GENERIC_CPU_VULNERABILITIES
 	select GENERIC_EARLY_IOREMAP
 	select GENERIC_FIND_FIRST_BIT
 	select GENERIC_IOMAP
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -10,6 +10,7 @@
  */
 #include <linux/init.h>
 #include <linux/utsname.h>
+#include <linux/cpu.h>
 #include <asm/bugs.h>
 #include <asm/processor.h>
 #include <asm/processor-flags.h>
@@ -60,3 +61,31 @@ void __init check_bugs(void)
 		set_memory_4k((unsigned long)__va(0), 1);
 #endif
 }
+
+#ifdef CONFIG_SYSFS
+ssize_t cpu_show_meltdown(struct device *dev,
+			  struct device_attribute *attr, char *buf)
+{
+	if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
+		return sprintf(buf, "Not affected\n");
+	if (boot_cpu_has(X86_FEATURE_PTI))
+		return sprintf(buf, "Mitigation: PTI\n");
+	return sprintf(buf, "Vulnerable\n");
+}
+
+ssize_t cpu_show_spectre_v1(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1))
+		return sprintf(buf, "Not affected\n");
+	return sprintf(buf, "Vulnerable\n");
+}
+
+ssize_t cpu_show_spectre_v2(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
+		return sprintf(buf, "Not affected\n");
+	return sprintf(buf, "Vulnerable\n");
+}
+#endif

Re: [patch V2 2/2] x86/cpu: Implement CPU vulnerabilites sysfs functions

[Konrad Rzeszutek Wilk]

On Sun, Jan 07, 2018 at 10:48:01PM +0100, Thomas Gleixner wrote:
> Implement the CPU vulnerabilty show functions for meltdown, spectre_v1 and
> spectre_v2.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Thank you!
> ---
>  arch/x86/Kconfig           |    1 +
>  arch/x86/kernel/cpu/bugs.c |   29 +++++++++++++++++++++++++++++
>  2 files changed, 30 insertions(+)
> 
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -89,6 +89,7 @@ config X86
>  	select GENERIC_CLOCKEVENTS_MIN_ADJUST
>  	select GENERIC_CMOS_UPDATE
>  	select GENERIC_CPU_AUTOPROBE
> +	select GENERIC_CPU_VULNERABILITIES
>  	select GENERIC_EARLY_IOREMAP
>  	select GENERIC_FIND_FIRST_BIT
>  	select GENERIC_IOMAP
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -10,6 +10,7 @@
>   */
>  #include <linux/init.h>
>  #include <linux/utsname.h>
> +#include <linux/cpu.h>
>  #include <asm/bugs.h>
>  #include <asm/processor.h>
>  #include <asm/processor-flags.h>
> @@ -60,3 +61,31 @@ void __init check_bugs(void)
>  		set_memory_4k((unsigned long)__va(0), 1);
>  #endif
>  }
> +
> +#ifdef CONFIG_SYSFS
> +ssize_t cpu_show_meltdown(struct device *dev,
> +			  struct device_attribute *attr, char *buf)
> +{
> +	if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
> +		return sprintf(buf, "Not affected\n");
> +	if (boot_cpu_has(X86_FEATURE_PTI))
> +		return sprintf(buf, "Mitigation: PTI\n");
> +	return sprintf(buf, "Vulnerable\n");
> +}
> +
> +ssize_t cpu_show_spectre_v1(struct device *dev,
> +			    struct device_attribute *attr, char *buf)
> +{
> +	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1))
> +		return sprintf(buf, "Not affected\n");
> +	return sprintf(buf, "Vulnerable\n");
> +}
> +
> +ssize_t cpu_show_spectre_v2(struct device *dev,
> +			    struct device_attribute *attr, char *buf)
> +{
> +	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
> +		return sprintf(buf, "Not affected\n");
> +	return sprintf(buf, "Vulnerable\n");
> +}
> +#endif
> 
> 

Re: [patch V2 2/2] x86/cpu: Implement CPU vulnerabilites sysfs functions

[Greg Kroah-Hartman]

On Sun, Jan 07, 2018 at 10:48:01PM +0100, Thomas Gleixner wrote:
> Implement the CPU vulnerabilty show functions for meltdown, spectre_v1 and
> spectre_v2.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/Kconfig           |    1 +
>  arch/x86/kernel/cpu/bugs.c |   29 +++++++++++++++++++++++++++++
>  2 files changed, 30 insertions(+)

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[tip:x86/pti] x86/cpu: Implement CPU vulnerabilites sysfs functions

[tip-bot for Thomas Gleixner]

Commit-ID:  61dc0f555b5c761cdafb0ba5bd41ecf22d68a4c4
Gitweb:     https://git.kernel.org/tip/61dc0f555b5c761cdafb0ba5bd41ecf22d68a4c4
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Sun, 7 Jan 2018 22:48:01 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Mon, 8 Jan 2018 11:10:40 +0100

x86/cpu: Implement CPU vulnerabilites sysfs functions

Implement the CPU vulnerabilty show functions for meltdown, spectre_v1 and
spectre_v2.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lkml.kernel.org/r/20180107214913.177414879@linutronix.de

---
 arch/x86/Kconfig           |  1 +
 arch/x86/kernel/cpu/bugs.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cd5199d..e23d21a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -89,6 +89,7 @@ config X86
 	select GENERIC_CLOCKEVENTS_MIN_ADJUST
 	select GENERIC_CMOS_UPDATE
 	select GENERIC_CPU_AUTOPROBE
+	select GENERIC_CPU_VULNERABILITIES
 	select GENERIC_EARLY_IOREMAP
 	select GENERIC_FIND_FIRST_BIT
 	select GENERIC_IOMAP
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ba0b242..76ad6cb 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -10,6 +10,7 @@
  */
 #include <linux/init.h>
 #include <linux/utsname.h>
+#include <linux/cpu.h>
 #include <asm/bugs.h>
 #include <asm/processor.h>
 #include <asm/processor-flags.h>
@@ -60,3 +61,31 @@ void __init check_bugs(void)
 		set_memory_4k((unsigned long)__va(0), 1);
 #endif
 }
+
+#ifdef CONFIG_SYSFS
+ssize_t cpu_show_meltdown(struct device *dev,
+			  struct device_attribute *attr, char *buf)
+{
+	if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
+		return sprintf(buf, "Not affected\n");
+	if (boot_cpu_has(X86_FEATURE_PTI))
+		return sprintf(buf, "Mitigation: PTI\n");
+	return sprintf(buf, "Vulnerable\n");
+}
+
+ssize_t cpu_show_spectre_v1(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1))
+		return sprintf(buf, "Not affected\n");
+	return sprintf(buf, "Vulnerable\n");
+}
+
+ssize_t cpu_show_spectre_v2(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
+		return sprintf(buf, "Not affected\n");
+	return sprintf(buf, "Vulnerable\n");
+}
+#endif