Messages in this thread | | | Date | Wed, 17 Apr 2024 19:01:54 +0100 | Subject | Re: [PATCH v3] x86/bugs: Only harden syscalls when needed | From | Andrew Cooper <> |
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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.
~Andrew
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