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SubjectRe: [PATCH v3] x86/bugs: Only harden syscalls when needed
On Wed, Apr 17, 2024 at 04:14:26PM +0100, Andrew Cooper wrote:
> On 17/04/2024 12:02 am, Josh Poimboeuf wrote:
> > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> > index ca295b0c1eee..dcb97cc2758f 100644
> > --- a/arch/x86/kernel/cpu/bugs.c
> > +++ b/arch/x86/kernel/cpu/bugs.c
> > @@ -1678,6 +1687,21 @@ static void __init spectre_v2_select_mitigation(void)
> > enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
> > enum spectre_v2_mitigation mode = SPECTRE_V2_NONE;
> >
> > + /*
> > + * X86_FEATURE_INDIRECT_SAFE indicates whether indirect calls can be
> > + * considered safe. That means either:
> > + *
> > + * - the CPU isn't vulnerable to Spectre v2 or its variants;
> > + *
> > + * - a hardware mitigation is in place (e.g., IBRS, BHI_DIS_S); or
> > + *
> > + * - the user turned off mitigations altogether.
> > + *
> > + * Assume innocence until proven guilty: set the cap bit now, then
> > + * clear it later if/when needed.
> > + */
> > + setup_force_cpu_cap(X86_FEATURE_INDIRECT_SAFE);
>
> Following on from the (re)discovery that X86_FEATURE_RETPOLINE is a poor
> name given what it *actually* does, can I recommend s/SAFE/OK/ here?

Or simply X86_FEATURE_USE_INDIRECT_BRANCH.

> This flag really is "do I want indirect branches or not", which - as
> noted here - is more than just a judgement of whether indirect branches
> are "safe".

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