diff mbox series

[v3,4/6] x86/bugs: Don't fill RSB on VMEXIT with eIBRS+retpoline

Message ID a305206cd08cde28c46a1ef19f5668a3fff9b013.1743617897.git.jpoimboe@kernel.org (mailing list archive)
State New
Headers show
Series x86/bugs: RSB mitigation fixes and documentation | expand

Commit Message

Josh Poimboeuf April 2, 2025, 6:19 p.m. UTC 
eIBRS protects against guest->host RSB underflow/poisoning attacks.
Adding retpoline to the mix doesn't change that.  Retpoline has a
balanced CALL/RET anyway.

So the current full RSB filling on VMEXIT with eIBRS+retpoline is
overkill.  Disable it or do the VMEXIT_LITE mitigation if needed.

Suggested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Amit Shah <amit.shah@amd.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/x86/kernel/cpu/bugs.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Nikolay Borisov April 8, 2025, 1:50 p.m. UTC | #1 
On 2.04.25 г. 21:19 ч., Josh Poimboeuf wrote:
> eIBRS protects against guest->host RSB underflow/poisoning attacks.
> Adding retpoline to the mix doesn't change that.  Retpoline has a
> balanced CALL/RET anyway.
> 
> So the current full RSB filling on VMEXIT with eIBRS+retpoline is
> overkill.  Disable it or do the VMEXIT_LITE mitigation if needed.
> 
> Suggested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Reviewed-by: Amit Shah <amit.shah@amd.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
diff mbox series

Patch

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 9f9637cff7a3..354411fd4800 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1617,20 +1617,20 @@  static void __init spectre_v2_determine_rsb_fill_type_at_vmexit(enum spectre_v2_
 	case SPECTRE_V2_NONE:
 		return;
 
-	case SPECTRE_V2_EIBRS_LFENCE:
 	case SPECTRE_V2_EIBRS:
+	case SPECTRE_V2_EIBRS_LFENCE:
+	case SPECTRE_V2_EIBRS_RETPOLINE:
 		if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) {
-			setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE);
 			pr_info("Spectre v2 / PBRSB-eIBRS: Retire a single CALL on VMEXIT\n");
+			setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE);
 		}
 		return;
 
-	case SPECTRE_V2_EIBRS_RETPOLINE:
 	case SPECTRE_V2_RETPOLINE:
 	case SPECTRE_V2_LFENCE:
 	case SPECTRE_V2_IBRS:
-		setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT);
 		pr_info("Spectre v2 / SpectreRSB : Filling RSB on VMEXIT\n");
+		setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT);
 		return;
 	}