Messages in this thread | | | Date | Thu, 18 Apr 2024 18:14:45 -0700 | From | Pawan Gupta <> | Subject | Re: [PATCH v3] x86/bugs: Only harden syscalls when needed |
| |
On Thu, Apr 18, 2024 at 05:48:45PM -0700, Josh Poimboeuf wrote: > On Wed, Apr 17, 2024 at 07:01:54PM +0100, Andrew Cooper wrote: > > On 17/04/2024 6:57 pm, Josh Poimboeuf wrote: > > > On Wed, Apr 17, 2024 at 09:45:14AM -0700, Pawan Gupta wrote: > > >> 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". > > > X86_FEATURE_USE_INDIRECT_BRANCH sounds good. It's a bit long but does > > > describe it better. > > > > Works for me. Definitely an improvement over SAFE. > > USE_INDIRECT_BRANCH is now irking me: "use indirect branch for what? > when? why?"
I don't think feature bits in general tries to answer when & why. And it shouldn't be the case, otherwise we will need multi-line names. IMO, it should just tell what the feature means. But, I am not too hung up on name, I am fine with X86_FEATURE_INDIRECT_OK or anything similar.
| |