Re: [PATCH v2 04/39] x86/cpufeatures: Enable CET CR4 bit for shadow stack

[Borislav Petkov]

On Thu, Sep 29, 2022 at 03:29:01PM -0700, Rick Edgecombe wrote:
>  static __always_inline void setup_cet(struct cpuinfo_x86 *c)
>  {
> -	u64 msr = CET_ENDBR_EN;
> +	bool kernel_ibt = HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT);

So I'd love it if we can get rid of that HAS_KERNEL_IBT thing and use
the usual ifdeffery with Kconfig symbols. I wouldn't like for yet
another HAS_XXX feature checking method to proliferate as this is the
only one:

$ git grep -E "\WHAS_" arch/x86/
arch/x86/include/asm/ibt.h:18: * When all the above are satisfied, HAS_KERNEL_IBT will be 1, otherwise 0.
arch/x86/include/asm/ibt.h:22:#define HAS_KERNEL_IBT    1
arch/x86/include/asm/ibt.h:92:#define HAS_KERNEL_IBT    0
arch/x86/include/asm/ibt.h:114:#define ENDBR_INSN_SIZE          (4*HAS_KERNEL_IBT)
arch/x86/include/asm/idtentry.h:8:#define IDT_ALIGN     (8 * (1 + HAS_KERNEL_IBT))
arch/x86/kernel/cpu/common.c:601:       bool kernel_ibt = HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT);
arch/x86/kernel/cpu/common.c:1942:      if (HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT))

>  __noendbr void cet_disable(void)
>  {
> -	if (cpu_feature_enabled(X86_FEATURE_IBT))
> -		wrmsrl(MSR_IA32_S_CET, 0);
> +	if (!(cpu_feature_enabled(X86_FEATURE_IBT) ||
> +	      cpu_feature_enabled(X86_FEATURE_SHSTK)))
> +		return;
> +
> +	wrmsrl(MSR_IA32_S_CET, 0);
> +	wrmsrl(MSR_IA32_U_CET, 0);
>  }
>  
> +

Stray newline.

-- 
Regards/Gruss,
    Boris.

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