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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: fb3bd914b3 ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814121149.109557833@infradead.org
This commit is contained in:
Peter Zijlstra 2023-08-14 13:44:35 +02:00 committed by Borislav Petkov (AMD)
parent e7c25c441e
commit 864bcaa38e
3 changed files with 14 additions and 5 deletions
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11
arch/x86/include/asm/nospec-branch.h
View File

@ -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)

1
arch/x86/kernel/cpu/bugs.c
View File

@ -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;

7
arch/x86/kvm/svm/vmenter.S
View File

@ -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