The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: ad63073765fa394665bcb54660cc997f05b704d4
Gitweb: https://git.kernel.org/tip/ad63073765fa394665bcb54660cc997f05b704d4
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Mon, 14 Aug 2023 13:44:35 +02:00
Committer: Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Wed, 16 Aug 2023 09:39:16 +02:00
x86/cpu/kvm: Provide UNTRAIN_RET_VM
Similar to how it doesn't make sense to have UNTRAIN_RET have two
untrain calls, it also doesn't make sense for VMEXIT to have an extra
IBPB call.
This cures VMEXIT doing potentially unret+IBPB or double IBPB.
Also, the (SEV) VMEXIT case seems to have been overlooked.
Redefine the meaning of the synthetic IBPB flags to:
- ENTRY_IBPB -- issue IBPB on entry (was: entry + VMEXIT)
- IBPB_ON_VMEXIT -- issue IBPB on VMEXIT
And have 'retbleed=ibpb' set *BOTH* feature flags to ensure it retains
the previous behaviour and issues IBPB on entry+VMEXIT.
The new 'srso=ibpb_vmexit' option only sets IBPB_ON_VMEXIT.
Create UNTRAIN_RET_VM specifically for the VMEXIT case, and have that
check IBPB_ON_VMEXIT.
All this avoids having the VMEXIT case having to check both ENTRY_IBPB
and IBPB_ON_VMEXIT and simplifies the alternatives.
Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230814121149.109557833@xxxxxxxxxxxxx
---
arch/x86/include/asm/nospec-branch.h | 11 +++++++++++
arch/x86/kernel/cpu/bugs.c | 1 +
arch/x86/kvm/svm/vmenter.S | 7 ++-----
3 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 5285c8e..c55cc24 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -299,6 +299,17 @@
#endif
.endm
+.macro UNTRAIN_RET_VM
+#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY) || \
+ defined(CONFIG_CALL_DEPTH_TRACKING) || defined(CONFIG_CPU_SRSO)
+ VALIDATE_UNRET_END
+ ALTERNATIVE_3 "", \
+ CALL_UNTRAIN_RET, X86_FEATURE_UNRET, \
+ "call entry_ibpb", X86_FEATURE_IBPB_ON_VMEXIT, \
+ __stringify(RESET_CALL_DEPTH), X86_FEATURE_CALL_DEPTH
+#endif
+.endm
+
.macro UNTRAIN_RET_FROM_CALL
#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY) || \
defined(CONFIG_CALL_DEPTH_TRACKING)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6f3e195..9026e3f 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1054,6 +1054,7 @@ do_cmd_auto:
case RETBLEED_MITIGATION_IBPB:
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
mitigate_smt = true;
break;
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 265452f..ef2ebab 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -222,10 +222,7 @@ SYM_FUNC_START(__svm_vcpu_run)
* because interrupt handlers won't sanitize 'ret' if the return is
* from the kernel.
*/
- UNTRAIN_RET
-
- /* SRSO */
- ALTERNATIVE "", "call entry_ibpb", X86_FEATURE_IBPB_ON_VMEXIT
+ UNTRAIN_RET_VM
/*
* Clear all general purpose registers except RSP and RAX to prevent
@@ -362,7 +359,7 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
* because interrupt handlers won't sanitize RET if the return is
* from the kernel.
*/
- UNTRAIN_RET
+ UNTRAIN_RET_VM
/* "Pop" @spec_ctrl_intercepted. */
pop %_ASM_BX
|