* [PATCH] x86/bugs: Select best SRSO mitigation
@ 2025-07-21 16:03 David Kaplan
2025-08-11 15:48 ` [tip: x86/urgent] " tip-bot2 for David Kaplan
0 siblings, 1 reply; 2+ messages in thread
From: David Kaplan @ 2025-07-21 16:03 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
The SRSO bug can theoretically be used to conduct user->user or
guest->guest attacks and requires a mitigation (namely IBPB instead of SBPB
on context switch) for these. So mark SRSO as being applicable to the
user->user and guest->guest attack vectors.
Additionally, SRSO supports multiple mitigations which mitigate different
potential attack vectors. Some CPUs are also immune to SRSO from
certain attack vectors (like user->kernel).
Use the specific attack vectors requiring mitigation to select the best
SRSO mitigation to avoid unnecessary performance hits.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
---
.../admin-guide/hw-vuln/attack_vector_controls.rst | 2 +-
arch/x86/kernel/cpu/bugs.c | 13 +++++++++++--
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst b/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
index b4de16f5ec44..6dd0800146f6 100644
--- a/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
+++ b/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
@@ -214,7 +214,7 @@ Spectre_v1 X
Spectre_v2 X X
Spectre_v2_user X X * (Note 1)
SRBDS X X X X
-SRSO X X
+SRSO X X X X
SSB (Note 4)
TAA X X X X * (Note 2)
TSA X X X X
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b74bf937cd9f..2186a771b9fc 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -386,7 +386,6 @@ static bool __init should_mitigate_vuln(unsigned int bug)
case X86_BUG_SPECTRE_V2:
case X86_BUG_RETBLEED:
- case X86_BUG_SRSO:
case X86_BUG_L1TF:
case X86_BUG_ITS:
return cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) ||
@@ -3184,8 +3183,18 @@ static void __init srso_select_mitigation(void)
}
if (srso_mitigation == SRSO_MITIGATION_AUTO) {
- if (should_mitigate_vuln(X86_BUG_SRSO)) {
+ /*
+ * Use safe-RET if user->kernel or guest->host protection is
+ * required. Otherwise the 'microcode' mitigation is sufficient
+ * to protect the user->user and guest->guest vectors.
+ */
+ if (cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST) ||
+ (cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) &&
+ !boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO))) {
srso_mitigation = SRSO_MITIGATION_SAFE_RET;
+ } else if (cpu_attack_vector_mitigated(CPU_MITIGATE_USER_USER) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_GUEST)) {
+ srso_mitigation = SRSO_MITIGATION_MICROCODE;
} else {
srso_mitigation = SRSO_MITIGATION_NONE;
return;
base-commit: 34481698fd9c3c21425ab744e9e15dc2ce3b1b85
--
2.34.1
^ permalink raw reply [flat|nested] 2+ messages in thread
* [tip: x86/urgent] x86/bugs: Select best SRSO mitigation
2025-07-21 16:03 [PATCH] x86/bugs: Select best SRSO mitigation David Kaplan
@ 2025-08-11 15:48 ` tip-bot2 for David Kaplan
0 siblings, 0 replies; 2+ messages in thread
From: tip-bot2 for David Kaplan @ 2025-08-11 15:48 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/urgent branch of tip:
Commit-ID: 4fa7d880aeb8cdbdaa4fb72be3e53ac1d6bcc088
Gitweb: https://git.kernel.org/tip/4fa7d880aeb8cdbdaa4fb72be3e53ac1d6bcc088
Author: David Kaplan <david.kaplan@amd.com>
AuthorDate: Mon, 21 Jul 2025 11:03:10 -05:00
Committer: Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Mon, 11 Aug 2025 17:32:36 +02:00
x86/bugs: Select best SRSO mitigation
The SRSO bug can theoretically be used to conduct user->user or guest->guest
attacks and requires a mitigation (namely IBPB instead of SBPB on context
switch) for these. So mark SRSO as being applicable to the user->user and
guest->guest attack vectors.
Additionally, SRSO supports multiple mitigations which mitigate different
potential attack vectors. Some CPUs are also immune to SRSO from
certain attack vectors (like user->kernel).
Use the specific attack vectors requiring mitigation to select the best
SRSO mitigation to avoid unnecessary performance hits.
Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250721160310.1804203-1-david.kaplan@amd.com
---
Documentation/admin-guide/hw-vuln/attack_vector_controls.rst | 2 +-
arch/x86/kernel/cpu/bugs.c | 13 +++++--
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst b/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
index b4de16f..6dd0800 100644
--- a/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
+++ b/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
@@ -214,7 +214,7 @@ Spectre_v1 X
Spectre_v2 X X
Spectre_v2_user X X * (Note 1)
SRBDS X X X X
-SRSO X X
+SRSO X X X X
SSB (Note 4)
TAA X X X X * (Note 2)
TSA X X X X
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b74bf93..2186a77 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -386,7 +386,6 @@ static bool __init should_mitigate_vuln(unsigned int bug)
case X86_BUG_SPECTRE_V2:
case X86_BUG_RETBLEED:
- case X86_BUG_SRSO:
case X86_BUG_L1TF:
case X86_BUG_ITS:
return cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) ||
@@ -3184,8 +3183,18 @@ static void __init srso_select_mitigation(void)
}
if (srso_mitigation == SRSO_MITIGATION_AUTO) {
- if (should_mitigate_vuln(X86_BUG_SRSO)) {
+ /*
+ * Use safe-RET if user->kernel or guest->host protection is
+ * required. Otherwise the 'microcode' mitigation is sufficient
+ * to protect the user->user and guest->guest vectors.
+ */
+ if (cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST) ||
+ (cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) &&
+ !boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO))) {
srso_mitigation = SRSO_MITIGATION_SAFE_RET;
+ } else if (cpu_attack_vector_mitigated(CPU_MITIGATE_USER_USER) ||
+ cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_GUEST)) {
+ srso_mitigation = SRSO_MITIGATION_MICROCODE;
} else {
srso_mitigation = SRSO_MITIGATION_NONE;
return;
^ permalink raw reply [flat|nested] 2+ messages in thread
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2025-08-11 15:48 ` [tip: x86/urgent] " tip-bot2 for David Kaplan
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