linux-kernel - Re: [PATCH v2 1/2] x86/stackprotector/32: Make the canary into a regular percpu variable

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Message-ID: <YCvw99dIJ9C90Q6R@google.com>
Date:   Tue, 16 Feb 2021 08:21:11 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Brian Gerst <brgerst@...il.com>, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH v2 1/2] x86/stackprotector/32: Make the canary into a
 regular percpu variable

On Sat, Feb 13, 2021, Andy Lutomirski wrote:
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index f923e14e87df..ec39073b4897 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1467,12 +1467,8 @@ static void svm_vcpu_put(struct kvm_vcpu *vcpu)
>  #ifdef CONFIG_X86_64
>  		loadsegment(fs, svm->host.fs);
>  		wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gsbase);
> -		load_gs_index(svm->host.gs);
> -#else
> -#ifdef CONFIG_X86_32_LAZY_GS
> -		loadsegment(gs, svm->host.gs);
> -#endif

This manually GS crud is gone as of commit e79b91bb3c91 ("KVM: SVM: use
vmsave/vmload for saving/restoring additional host state"), which is queued for
5.12.

>  #endif
> +		load_gs_index(svm->host.gs);
>  
>  		for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
>  			wrmsrl(host_save_user_msrs[i].index,
> @@ -3705,13 +3701,11 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu,
>  	} else {
>  		__svm_vcpu_run(svm->vmcb_pa, (unsigned long *)&svm->vcpu.arch.regs);
>  
> +		/* Restore the percpu segment immediately. */
>  #ifdef CONFIG_X86_64
>  		native_wrmsrl(MSR_GS_BASE, svm->host.gs_base);
>  #else
>  		loadsegment(fs, svm->host.fs);
> -#ifndef CONFIG_X86_32_LAZY_GS
> -		loadsegment(gs, svm->host.gs);
> -#endif
>  #endif
>  	}