cpufeatures.h defines X86_FEATURE_RSB_CTXSW as "Fill RSB on context
switches" which seems more accurate than using X86_FEATURE_RETPOLINE
in the vmxexit path for RSB stuffing.
X86_FEATURE_RSB_CTXSW is used for FILL_RETURN_BUFFER in
arch/x86/entry/entry_{32|64}.S. This change makes KVM vmx and svm
follow that same pattern. This pairs up nicely with the language in
bugs.c, where this cpu_cap is enabled, which indicates that RSB
stuffing should be unconditional with spectrev2 enabled.
/*
* If spectre v2 protection has been enabled, unconditionally fill
* RSB during a context switch; this protects against two independent
* issues:
*
* - RSB underflow (and switch to BTB) on Skylake+
* - SpectreRSB variant of spectre v2 on X86_BUG_SPECTRE_V2 CPUs
*/
setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
Furthermore, on X86_FEATURE_IBRS_ENHANCED CPUs && SPECTRE_V2_CMD_AUTO,
we're bypassing setting X86_FEATURE_RETPOLINE, where as far as I could
find, we should still be doing RSB stuffing no matter what when
CONFIG_RETPOLINE is enabled and spectrev2 is set to auto.
Signed-off-by: Jon Kohler <jon@xxxxxxxxxxx>
---
arch/x86/kvm/svm/vmenter.S | 4 ++--
arch/x86/kvm/vmx/vmenter.S | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 4fa17df123cd..fe81012da4b5 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -86,7 +86,7 @@ SYM_FUNC_START(__svm_vcpu_run)
#ifdef CONFIG_RETPOLINE
/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
- FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
+ FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
#endif
/* "POP" @regs to RAX. */
@@ -187,7 +187,7 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
#ifdef CONFIG_RETPOLINE
/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
- FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
+ FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
#endif
pop %_ASM_BX
diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 3a6461694fc2..ede6aac7d8b7 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -76,12 +76,12 @@ SYM_FUNC_END(vmx_vmenter)
*/
SYM_FUNC_START(vmx_vmexit)
#ifdef CONFIG_RETPOLINE
- ALTERNATIVE "jmp .Lvmexit_skip_rsb", "", X86_FEATURE_RETPOLINE
+ ALTERNATIVE "jmp .Lvmexit_skip_rsb", "", X86_FEATURE_RSB_CTXSW
/* Preserve guest's RAX, it's used to stuff the RSB. */
push %_ASM_AX
/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
- FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
+ FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
/* Clear RFLAGS.CF and RFLAGS.ZF to preserve VM-Exit, i.e. !VM-Fail. */
or $1, %_ASM_AX
--
2.30.1 (Apple Git-130)
