The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 864bcaa38ee44ec6c0e43f79c2d2997b977e26b2 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2023082126-yanking-circling-2487@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

864bcaa38ee4 ("x86/cpu/kvm: Provide UNTRAIN_RET_VM") d893832d0e1e ("x86/srso: Add IBPB on VMEXIT") 233d6f68b98d ("x86/srso: Add IBPB") fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation") 941d77c77339 ("Merge tag 'x86_cpu_for_v6.5' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 864bcaa38ee44ec6c0e43f79c2d2997b977e26b2 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra peterz@infradead.org Date: Mon, 14 Aug 2023 13:44:35 +0200 Subject: [PATCH] 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@infradead.org Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Link: https://lore.kernel.org/r/20230814121149.109557833@infradead.org

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 5285c8e93dff..c55cc243592e 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 6f3e19527286..9026e3fe9f6c 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1054,6 +1054,7 @@ static void __init retbleed_select_mitigation(void)

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 265452fc9ebe..ef2ebabb059c 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