linux-kernel - Re: [PATCH 03/19] x86/cpufeatures: Enable CET CR4 bit for shadow stack

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Message-ID: <YqsEyoaxPFpZcolP@hirez.programming.kicks-ass.net>
Date:   Thu, 16 Jun 2022 12:24:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, seanjc@...gle.com, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rick.p.edgecombe@...el.com, Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 03/19] x86/cpufeatures: Enable CET CR4 bit for shadow
 stack

On Thu, Jun 16, 2022 at 04:46:27AM -0400, Yang Weijiang wrote:
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -74,7 +74,7 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c);
>  static inline void init_ia32_feat_ctl(struct cpuinfo_x86 *c) {}
>  #endif
>  
> -extern __noendbr void cet_disable(void);
> +extern __noendbr void ibt_disable(void);
>  
>  struct ucode_cpu_info;
>  
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index c296cb1c0113..86102a8d451e 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -598,23 +598,23 @@ __noendbr void ibt_restore(u64 save)

>  
> -__noendbr void cet_disable(void)
> +__noendbr void ibt_disable(void)
>  {
>  	if (cpu_feature_enabled(X86_FEATURE_IBT))
>  		wrmsrl(MSR_IA32_S_CET, 0);

Not sure about this rename; it really disables all of (S) CET.

Specifically, once we do S-SHSTK (after FRED) we might also very much
need to kill that for kexec.

> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index 0611fd83858e..745024654fcd 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -311,7 +311,7 @@ void machine_kexec(struct kimage *image)
>  	/* Interrupts aren't acceptable while we reboot */
>  	local_irq_disable();
>  	hw_breakpoint_disable();
> -	cet_disable();
> +	ibt_disable();
>  
>  	if (image->preserve_context) {
>  #ifdef CONFIG_X86_IO_APIC
> -- 
> 2.27.0
>