From: "Borislav Petkov (AMD)" bp@alien8.de
stable inclusion from stable-v5.10.189 commit df76a59feba549825f426cb1586bfa86b49c08fa category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/I7RQ67 CVE: CVE-2023-20569
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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Upstream commit: 79113e4060aba744787a81edb9014f2865193854
Add support for the synthetic CPUID flag which "if this bit is 1, it indicates that MSR 49h (PRED_CMD) bit 0 (IBPB) flushes all branch type predictions from the CPU branch predictor."
This flag is there so that this capability in guests can be detected easily (otherwise one would have to track microcode revisions which is impossible for guests).
It is also needed only for Zen3 and -4. The other two (Zen1 and -2) always flush branch type predictions by default.
Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
Conflicts: arch/x86/include/asm/cpufeatures.h
Signed-off-by: Jialin Zhang zhangjialin11@huawei.com --- arch/x86/include/asm/cpufeatures.h | 2 ++ arch/x86/kernel/cpu/bugs.c | 12 +++++++++++- 2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index d40732084e20..868263f52aeb 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -416,6 +416,8 @@ #define X86_FEATURE_SPEC_CTRL_SSBD (18*32+31) /* "" Speculative Store Bypass Disable */
+#define X86_FEATURE_IBPB_BRTYPE (19*32+28) /* "" MSR_PRED_CMD[IBPB] flushes all branch type predictions */ + /* * BUG word(s) */ diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 42aad57abf3e..d0d88dbaed5c 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -2286,10 +2286,20 @@ static void __init srso_select_mitigation(void) if (!boot_cpu_has_bug(X86_BUG_SRSO) || cpu_mitigations_off()) return;
- has_microcode = cpu_has_ibpb_brtype_microcode(); + /* + * The first check is for the kernel running as a guest in order + * for guests to verify whether IBPB is a viable mitigation. + */ + has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE) || cpu_has_ibpb_brtype_microcode(); if (!has_microcode) { pr_warn("IBPB-extending microcode not applied!\n"); pr_warn(SRSO_NOTICE); + } else { + /* + * Enable the synthetic (even if in a real CPUID leaf) + * flag for guests. + */ + setup_force_cpu_cap(X86_FEATURE_IBPB_BRTYPE); }
switch (srso_cmd) {