From: Sean Christopherson <seanjc@google.com>
To: "Mika Penttilä" <mpenttil@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Srikanth Aithal <sraithal@amd.com>,
kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] x86/retpoline: Don't clobber RFLAGS during srso_safe_ret()
Date: Fri, 11 Aug 2023 19:57:22 -0700 [thread overview]
Message-ID: <ZNb1EpG1GDzRspPB@google.com> (raw)
In-Reply-To: <8edc91f9-ce20-9528-a496-5b6e650bb63f@redhat.com>
On Fri, Aug 11, 2023, Mika Penttilä wrote:
> > @@ -252,11 +252,10 @@ SYM_START(srso_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
> > .byte 0x48, 0xb8
> > SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLOBAL)
> > - add $8, %_ASM_SP
> > + lea 8(%_ASM_SP), %_ASM_SP
> > ret
> > int3
> > int3
> > - int3
> > lfence
> > call srso_safe_ret
> > int3
> >
> > base-commit: 25aa0bebba72b318e71fe205bfd1236550cc9534
>
> Don't we have the same kind of problems with __x86_return_skl ?
Yep, forcing that path via "retbleed=force retbleed=stuff spectre_v2=retpoline,generic"
yields the same failures. I have no idea how to go about cleanly fixing that.
The logic effectively requires modifying flags, the only thing I can think of is
to save/restore flags across the thunk, which seems beyond gross.
Given that no one has complained about this, I think I'd vote to simply disable
KVM if call depth tracking is being used.
next prev parent reply other threads:[~2023-08-12 2:57 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-11 15:52 [PATCH] x86/retpoline: Don't clobber RFLAGS during srso_safe_ret() Sean Christopherson
2023-08-11 17:28 ` Nathan Chancellor
2023-08-11 18:05 ` Borislav Petkov
2023-08-12 2:59 ` Sean Christopherson
2023-08-11 18:47 ` Mika Penttilä
2023-08-12 2:57 ` Sean Christopherson [this message]
2023-08-14 9:07 ` [tip: x86/urgent] " tip-bot2 for Sean Christopherson
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