* [PATCH 1/3] x86/bugs: Add SRSO_MITIGATION_NOSMT
2025-06-25 15:58 [PATCH 0/3] SRSO fixes David Kaplan
@ 2025-06-25 15:58 ` David Kaplan
2025-06-26 9:10 ` [tip: x86/bugs] " tip-bot2 for David Kaplan
2025-06-25 15:58 ` [PATCH 2/3] x86/bugs: Use IBPB for retbleed if used by SRSO David Kaplan
2025-06-25 15:58 ` [PATCH 3/3] x86/bugs: Clean up SRSO ucode handling David Kaplan
2 siblings, 1 reply; 7+ messages in thread
From: David Kaplan @ 2025-06-25 15:58 UTC (permalink / raw)
To: Thomas Gleixner, Borislav Petkov, Peter Zijlstra, Josh Poimboeuf,
Pawan Gupta, Ingo Molnar, Dave Hansen, x86, H . Peter Anvin
Cc: linux-kernel
Zen1 and Zen2 CPUs with SMT disabled are not vulnerable to SRSO.
Instead of overloading the X86_FEATURE_SRSO_NO bit to indicate this,
define a separate mitigation to make the code cleaner.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
---
arch/x86/kernel/cpu/bugs.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index bdef2c9aa1b8..6c991afb7b78 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2851,6 +2851,7 @@ enum srso_mitigation {
SRSO_MITIGATION_UCODE_NEEDED,
SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
SRSO_MITIGATION_MICROCODE,
+ SRSO_MITIGATION_NOSMT,
SRSO_MITIGATION_SAFE_RET,
SRSO_MITIGATION_IBPB,
SRSO_MITIGATION_IBPB_ON_VMEXIT,
@@ -2862,6 +2863,7 @@ static const char * const srso_strings[] = {
[SRSO_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
[SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED] = "Vulnerable: Safe RET, no microcode",
[SRSO_MITIGATION_MICROCODE] = "Vulnerable: Microcode, no safe RET",
+ [SRSO_MITIGATION_NOSMT] = "Mitigation: SMT disabled",
[SRSO_MITIGATION_SAFE_RET] = "Mitigation: Safe RET",
[SRSO_MITIGATION_IBPB] = "Mitigation: IBPB",
[SRSO_MITIGATION_IBPB_ON_VMEXIT] = "Mitigation: IBPB on VMEXIT only",
@@ -2914,8 +2916,7 @@ static void __init srso_select_mitigation(void)
* IBPB microcode has been applied.
*/
if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
- setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
- srso_mitigation = SRSO_MITIGATION_NONE;
+ srso_mitigation = SRSO_MITIGATION_NOSMT;
return;
}
} else {
@@ -2968,8 +2969,7 @@ static void __init srso_update_mitigation(void)
srso_mitigation = SRSO_MITIGATION_IBPB;
if (boot_cpu_has_bug(X86_BUG_SRSO) &&
- !cpu_mitigations_off() &&
- !boot_cpu_has(X86_FEATURE_SRSO_NO))
+ !cpu_mitigations_off())
pr_info("%s\n", srso_strings[srso_mitigation]);
}
@@ -3265,9 +3265,6 @@ static ssize_t retbleed_show_state(char *buf)
static ssize_t srso_show_state(char *buf)
{
- if (boot_cpu_has(X86_FEATURE_SRSO_NO))
- return sysfs_emit(buf, "Mitigation: SMT disabled\n");
-
return sysfs_emit(buf, "%s\n", srso_strings[srso_mitigation]);
}
--
2.34.1
^ permalink raw reply [flat|nested] 7+ messages in thread* [tip: x86/bugs] x86/bugs: Add SRSO_MITIGATION_NOSMT
2025-06-25 15:58 ` [PATCH 1/3] x86/bugs: Add SRSO_MITIGATION_NOSMT David Kaplan
@ 2025-06-26 9:10 ` tip-bot2 for David Kaplan
0 siblings, 0 replies; 7+ messages in thread
From: tip-bot2 for David Kaplan @ 2025-06-26 9:10 UTC (permalink / raw)
To: linux-tip-commits
Cc: David Kaplan, Ingo Molnar, Borislav Petkov (AMD),
H . Peter Anvin, Dave Hansen, Josh Poimboeuf, Pawan Gupta,
Peter Zijlstra, x86, linux-kernel
The following commit has been merged into the x86/bugs branch of tip:
Commit-ID: 1fd5eb02867ac7db9144bd44c8edfad0189c8e57
Gitweb: https://git.kernel.org/tip/1fd5eb02867ac7db9144bd44c8edfad0189c8e57
Author: David Kaplan <david.kaplan@amd.com>
AuthorDate: Wed, 25 Jun 2025 10:58:03 -05:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 26 Jun 2025 10:56:39 +02:00
x86/bugs: Add SRSO_MITIGATION_NOSMT
AMD Zen1 and Zen2 CPUs with SMT disabled are not vulnerable to SRSO.
Instead of overloading the X86_FEATURE_SRSO_NO bit to indicate this,
define a separate mitigation to make the code cleaner.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250625155805.600376-2-david.kaplan@amd.com
---
arch/x86/kernel/cpu/bugs.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index bdef2c9..6c991af 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2851,6 +2851,7 @@ enum srso_mitigation {
SRSO_MITIGATION_UCODE_NEEDED,
SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
SRSO_MITIGATION_MICROCODE,
+ SRSO_MITIGATION_NOSMT,
SRSO_MITIGATION_SAFE_RET,
SRSO_MITIGATION_IBPB,
SRSO_MITIGATION_IBPB_ON_VMEXIT,
@@ -2862,6 +2863,7 @@ static const char * const srso_strings[] = {
[SRSO_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
[SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED] = "Vulnerable: Safe RET, no microcode",
[SRSO_MITIGATION_MICROCODE] = "Vulnerable: Microcode, no safe RET",
+ [SRSO_MITIGATION_NOSMT] = "Mitigation: SMT disabled",
[SRSO_MITIGATION_SAFE_RET] = "Mitigation: Safe RET",
[SRSO_MITIGATION_IBPB] = "Mitigation: IBPB",
[SRSO_MITIGATION_IBPB_ON_VMEXIT] = "Mitigation: IBPB on VMEXIT only",
@@ -2914,8 +2916,7 @@ static void __init srso_select_mitigation(void)
* IBPB microcode has been applied.
*/
if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
- setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
- srso_mitigation = SRSO_MITIGATION_NONE;
+ srso_mitigation = SRSO_MITIGATION_NOSMT;
return;
}
} else {
@@ -2968,8 +2969,7 @@ static void __init srso_update_mitigation(void)
srso_mitigation = SRSO_MITIGATION_IBPB;
if (boot_cpu_has_bug(X86_BUG_SRSO) &&
- !cpu_mitigations_off() &&
- !boot_cpu_has(X86_FEATURE_SRSO_NO))
+ !cpu_mitigations_off())
pr_info("%s\n", srso_strings[srso_mitigation]);
}
@@ -3265,9 +3265,6 @@ static ssize_t retbleed_show_state(char *buf)
static ssize_t srso_show_state(char *buf)
{
- if (boot_cpu_has(X86_FEATURE_SRSO_NO))
- return sysfs_emit(buf, "Mitigation: SMT disabled\n");
-
return sysfs_emit(buf, "%s\n", srso_strings[srso_mitigation]);
}
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 2/3] x86/bugs: Use IBPB for retbleed if used by SRSO
2025-06-25 15:58 [PATCH 0/3] SRSO fixes David Kaplan
2025-06-25 15:58 ` [PATCH 1/3] x86/bugs: Add SRSO_MITIGATION_NOSMT David Kaplan
@ 2025-06-25 15:58 ` David Kaplan
2025-06-26 9:09 ` [tip: x86/bugs] " tip-bot2 for David Kaplan
2025-06-25 15:58 ` [PATCH 3/3] x86/bugs: Clean up SRSO ucode handling David Kaplan
2 siblings, 1 reply; 7+ messages in thread
From: David Kaplan @ 2025-06-25 15:58 UTC (permalink / raw)
To: Thomas Gleixner, Borislav Petkov, Peter Zijlstra, Josh Poimboeuf,
Pawan Gupta, Ingo Molnar, Dave Hansen, x86, H . Peter Anvin
Cc: linux-kernel
If spec_rstack_overflow=ibpb then this mitigates retbleed as well. This
is relevant for Zen1 and Zen2 CPUs which are vulnerable to both bugs.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
---
arch/x86/kernel/cpu/bugs.c | 34 +++++++++++++++++++---------------
1 file changed, 19 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6c991afb7b78..b26341983230 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1171,6 +1171,21 @@ static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
static int __ro_after_init retbleed_nosmt = false;
+enum srso_mitigation {
+ SRSO_MITIGATION_NONE,
+ SRSO_MITIGATION_AUTO,
+ SRSO_MITIGATION_UCODE_NEEDED,
+ SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
+ SRSO_MITIGATION_MICROCODE,
+ SRSO_MITIGATION_NOSMT,
+ SRSO_MITIGATION_SAFE_RET,
+ SRSO_MITIGATION_IBPB,
+ SRSO_MITIGATION_IBPB_ON_VMEXIT,
+ SRSO_MITIGATION_BP_SPEC_REDUCE,
+};
+
+static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO;
+
static int __init retbleed_parse_cmdline(char *str)
{
if (!str)
@@ -1280,6 +1295,10 @@ static void __init retbleed_update_mitigation(void)
if (its_mitigation == ITS_MITIGATION_RETPOLINE_STUFF)
retbleed_mitigation = RETBLEED_MITIGATION_STUFF;
+ /* If SRSO is using IBPB, that works for retbleed too */
+ if (srso_mitigation == SRSO_MITIGATION_IBPB)
+ retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
+
if (retbleed_mitigation == RETBLEED_MITIGATION_STUFF &&
!cdt_possible(spectre_v2_enabled)) {
pr_err("WARNING: retbleed=stuff depends on retpoline\n");
@@ -2845,19 +2864,6 @@ early_param("l1tf", l1tf_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "Speculative Return Stack Overflow: " fmt
-enum srso_mitigation {
- SRSO_MITIGATION_NONE,
- SRSO_MITIGATION_AUTO,
- SRSO_MITIGATION_UCODE_NEEDED,
- SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
- SRSO_MITIGATION_MICROCODE,
- SRSO_MITIGATION_NOSMT,
- SRSO_MITIGATION_SAFE_RET,
- SRSO_MITIGATION_IBPB,
- SRSO_MITIGATION_IBPB_ON_VMEXIT,
- SRSO_MITIGATION_BP_SPEC_REDUCE,
-};
-
static const char * const srso_strings[] = {
[SRSO_MITIGATION_NONE] = "Vulnerable",
[SRSO_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
@@ -2870,8 +2876,6 @@ static const char * const srso_strings[] = {
[SRSO_MITIGATION_BP_SPEC_REDUCE] = "Mitigation: Reduced Speculation"
};
-static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO;
-
static int __init srso_parse_cmdline(char *str)
{
if (!str)
--
2.34.1
^ permalink raw reply [flat|nested] 7+ messages in thread* [tip: x86/bugs] x86/bugs: Use IBPB for retbleed if used by SRSO
2025-06-25 15:58 ` [PATCH 2/3] x86/bugs: Use IBPB for retbleed if used by SRSO David Kaplan
@ 2025-06-26 9:09 ` tip-bot2 for David Kaplan
0 siblings, 0 replies; 7+ messages in thread
From: tip-bot2 for David Kaplan @ 2025-06-26 9:09 UTC (permalink / raw)
To: linux-tip-commits
Cc: David Kaplan, Ingo Molnar, Borislav Petkov (AMD),
H . Peter Anvin, Dave Hansen, Josh Poimboeuf, Pawan Gupta,
Peter Zijlstra, x86, linux-kernel
The following commit has been merged into the x86/bugs branch of tip:
Commit-ID: ff54ae7314962699749869a3475da7a702ae991a
Gitweb: https://git.kernel.org/tip/ff54ae7314962699749869a3475da7a702ae991a
Author: David Kaplan <david.kaplan@amd.com>
AuthorDate: Wed, 25 Jun 2025 10:58:04 -05:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 26 Jun 2025 10:56:39 +02:00
x86/bugs: Use IBPB for retbleed if used by SRSO
If spec_rstack_overflow=ibpb then this mitigates retbleed as well. This
is relevant for AMD Zen1 and Zen2 CPUs which are vulnerable to both bugs.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250625155805.600376-3-david.kaplan@amd.com
---
arch/x86/kernel/cpu/bugs.c | 34 +++++++++++++++++++---------------
1 file changed, 19 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6c991af..b263419 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1171,6 +1171,21 @@ static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
static int __ro_after_init retbleed_nosmt = false;
+enum srso_mitigation {
+ SRSO_MITIGATION_NONE,
+ SRSO_MITIGATION_AUTO,
+ SRSO_MITIGATION_UCODE_NEEDED,
+ SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
+ SRSO_MITIGATION_MICROCODE,
+ SRSO_MITIGATION_NOSMT,
+ SRSO_MITIGATION_SAFE_RET,
+ SRSO_MITIGATION_IBPB,
+ SRSO_MITIGATION_IBPB_ON_VMEXIT,
+ SRSO_MITIGATION_BP_SPEC_REDUCE,
+};
+
+static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO;
+
static int __init retbleed_parse_cmdline(char *str)
{
if (!str)
@@ -1280,6 +1295,10 @@ static void __init retbleed_update_mitigation(void)
if (its_mitigation == ITS_MITIGATION_RETPOLINE_STUFF)
retbleed_mitigation = RETBLEED_MITIGATION_STUFF;
+ /* If SRSO is using IBPB, that works for retbleed too */
+ if (srso_mitigation == SRSO_MITIGATION_IBPB)
+ retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
+
if (retbleed_mitigation == RETBLEED_MITIGATION_STUFF &&
!cdt_possible(spectre_v2_enabled)) {
pr_err("WARNING: retbleed=stuff depends on retpoline\n");
@@ -2845,19 +2864,6 @@ early_param("l1tf", l1tf_cmdline);
#undef pr_fmt
#define pr_fmt(fmt) "Speculative Return Stack Overflow: " fmt
-enum srso_mitigation {
- SRSO_MITIGATION_NONE,
- SRSO_MITIGATION_AUTO,
- SRSO_MITIGATION_UCODE_NEEDED,
- SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
- SRSO_MITIGATION_MICROCODE,
- SRSO_MITIGATION_NOSMT,
- SRSO_MITIGATION_SAFE_RET,
- SRSO_MITIGATION_IBPB,
- SRSO_MITIGATION_IBPB_ON_VMEXIT,
- SRSO_MITIGATION_BP_SPEC_REDUCE,
-};
-
static const char * const srso_strings[] = {
[SRSO_MITIGATION_NONE] = "Vulnerable",
[SRSO_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
@@ -2870,8 +2876,6 @@ static const char * const srso_strings[] = {
[SRSO_MITIGATION_BP_SPEC_REDUCE] = "Mitigation: Reduced Speculation"
};
-static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO;
-
static int __init srso_parse_cmdline(char *str)
{
if (!str)
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 3/3] x86/bugs: Clean up SRSO ucode handling
2025-06-25 15:58 [PATCH 0/3] SRSO fixes David Kaplan
2025-06-25 15:58 ` [PATCH 1/3] x86/bugs: Add SRSO_MITIGATION_NOSMT David Kaplan
2025-06-25 15:58 ` [PATCH 2/3] x86/bugs: Use IBPB for retbleed if used by SRSO David Kaplan
@ 2025-06-25 15:58 ` David Kaplan
2025-06-26 13:01 ` [tip: x86/bugs] x86/bugs: Clean up SRSO microcode handling tip-bot2 for David Kaplan
2 siblings, 1 reply; 7+ messages in thread
From: David Kaplan @ 2025-06-25 15:58 UTC (permalink / raw)
To: Thomas Gleixner, Borislav Petkov, Peter Zijlstra, Josh Poimboeuf,
Pawan Gupta, Ingo Molnar, Dave Hansen, x86, H . Peter Anvin
Cc: linux-kernel
SRSO ucode only exists for Zen3/Zen4 CPUs. For those CPUs, the ucode is
required for any mitigation other than Safe-RET to be effective. Safe-RET
can still protect user->kernel and guest->host attacks without ucode.
Clarify this in the code and ensure that SRSO_MITIGATION_UCODE_NEEDED is
selected for any mitigation besides Safe-RET if the required ucode isn't
present.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
arch/x86/kernel/cpu/bugs.c | 37 ++++++++++++++++++-------------------
1 file changed, 18 insertions(+), 19 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b26341983230..e2a8a21efb10 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2902,8 +2902,6 @@ early_param("spec_rstack_overflow", srso_parse_cmdline);
static void __init srso_select_mitigation(void)
{
- bool has_microcode;
-
if (!boot_cpu_has_bug(X86_BUG_SRSO) || cpu_mitigations_off())
srso_mitigation = SRSO_MITIGATION_NONE;
@@ -2913,23 +2911,30 @@ static void __init srso_select_mitigation(void)
if (srso_mitigation == SRSO_MITIGATION_AUTO)
srso_mitigation = SRSO_MITIGATION_SAFE_RET;
- has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
- if (has_microcode) {
- /*
- * Zen1/2 with SMT off aren't vulnerable after the right
- * IBPB microcode has been applied.
- */
- if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
- srso_mitigation = SRSO_MITIGATION_NOSMT;
- return;
- }
- } else {
+ /* Zen1/2 with SMT off aren't vulnerable to SRSO. */
+ if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
+ srso_mitigation = SRSO_MITIGATION_NOSMT;
+ return;
+ }
+
+ if (!boot_cpu_has(X86_FEATURE_IBPB_BRTYPE)) {
pr_warn("IBPB-extending microcode not applied!\n");
pr_warn(SRSO_NOTICE);
+
+ /*
+ * Safe-RET provides partial mitigation without microcode, but
+ * other mitigations require microcode to provide any
+ * mitigations.
+ */
+ if (srso_mitigation == SRSO_MITIGATION_SAFE_RET)
+ srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
+ else
+ srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED;
}
switch (srso_mitigation) {
case SRSO_MITIGATION_SAFE_RET:
+ case SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED:
if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO)) {
srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
goto ibpb_on_vmexit;
@@ -2939,9 +2944,6 @@ static void __init srso_select_mitigation(void)
pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
srso_mitigation = SRSO_MITIGATION_NONE;
}
-
- if (!has_microcode)
- srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
break;
ibpb_on_vmexit:
case SRSO_MITIGATION_IBPB_ON_VMEXIT:
@@ -2956,9 +2958,6 @@ static void __init srso_select_mitigation(void)
pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n");
srso_mitigation = SRSO_MITIGATION_NONE;
}
-
- if (!has_microcode)
- srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED;
break;
default:
break;
--
2.34.1
^ permalink raw reply [flat|nested] 7+ messages in thread* [tip: x86/bugs] x86/bugs: Clean up SRSO microcode handling
2025-06-25 15:58 ` [PATCH 3/3] x86/bugs: Clean up SRSO ucode handling David Kaplan
@ 2025-06-26 13:01 ` tip-bot2 for David Kaplan
0 siblings, 0 replies; 7+ messages in thread
From: tip-bot2 for David Kaplan @ 2025-06-26 13:01 UTC (permalink / raw)
To: linux-tip-commits; +Cc: David Kaplan, Borislav Petkov (AMD), x86, linux-kernel
The following commit has been merged into the x86/bugs branch of tip:
Commit-ID: 98b5dab4d22181c931f2bf63c060416badbb49ab
Gitweb: https://git.kernel.org/tip/98b5dab4d22181c931f2bf63c060416badbb49ab
Author: David Kaplan <david.kaplan@amd.com>
AuthorDate: Wed, 25 Jun 2025 10:58:05 -05:00
Committer: Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Thu, 26 Jun 2025 13:32:31 +02:00
x86/bugs: Clean up SRSO microcode handling
SRSO microcode only exists for Zen3/Zen4 CPUs. For those CPUs, the microcode
is required for any mitigation other than Safe-RET to be effective. Safe-RET
can still protect user->kernel and guest->host attacks without microcode.
Clarify this in the code and ensure that SRSO_MITIGATION_UCODE_NEEDED is
selected for any mitigation besides Safe-RET if the required microcode isn't
present.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250625155805.600376-4-david.kaplan@amd.com
---
arch/x86/kernel/cpu/bugs.c | 37 ++++++++++++++++++-------------------
1 file changed, 18 insertions(+), 19 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b263419..e2a8a21 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2902,8 +2902,6 @@ early_param("spec_rstack_overflow", srso_parse_cmdline);
static void __init srso_select_mitigation(void)
{
- bool has_microcode;
-
if (!boot_cpu_has_bug(X86_BUG_SRSO) || cpu_mitigations_off())
srso_mitigation = SRSO_MITIGATION_NONE;
@@ -2913,23 +2911,30 @@ static void __init srso_select_mitigation(void)
if (srso_mitigation == SRSO_MITIGATION_AUTO)
srso_mitigation = SRSO_MITIGATION_SAFE_RET;
- has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
- if (has_microcode) {
- /*
- * Zen1/2 with SMT off aren't vulnerable after the right
- * IBPB microcode has been applied.
- */
- if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
- srso_mitigation = SRSO_MITIGATION_NOSMT;
- return;
- }
- } else {
+ /* Zen1/2 with SMT off aren't vulnerable to SRSO. */
+ if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
+ srso_mitigation = SRSO_MITIGATION_NOSMT;
+ return;
+ }
+
+ if (!boot_cpu_has(X86_FEATURE_IBPB_BRTYPE)) {
pr_warn("IBPB-extending microcode not applied!\n");
pr_warn(SRSO_NOTICE);
+
+ /*
+ * Safe-RET provides partial mitigation without microcode, but
+ * other mitigations require microcode to provide any
+ * mitigations.
+ */
+ if (srso_mitigation == SRSO_MITIGATION_SAFE_RET)
+ srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
+ else
+ srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED;
}
switch (srso_mitigation) {
case SRSO_MITIGATION_SAFE_RET:
+ case SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED:
if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO)) {
srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
goto ibpb_on_vmexit;
@@ -2939,9 +2944,6 @@ static void __init srso_select_mitigation(void)
pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
srso_mitigation = SRSO_MITIGATION_NONE;
}
-
- if (!has_microcode)
- srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
break;
ibpb_on_vmexit:
case SRSO_MITIGATION_IBPB_ON_VMEXIT:
@@ -2956,9 +2958,6 @@ ibpb_on_vmexit:
pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n");
srso_mitigation = SRSO_MITIGATION_NONE;
}
-
- if (!has_microcode)
- srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED;
break;
default:
break;
^ permalink raw reply [flat|nested] 7+ messages in thread