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

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Date:   Tue, 16 Feb 2021 21:23:20 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        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 Tue, Feb 16, 2021 at 5:21 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> 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.
>

Link to the above KVM patch see [1].

As said the base for this patchset should be changed - for example it
conflicts with [2].

Maybe wait for Linux v5.12-rc1?

- Sedat -

[1] https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?h=tags/kvm-5.12-1&id=e79b91bb3c916a52ce823ab60489c717c925c49f
[2] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/tag/?h=x86-entry-2021-02-15

> >  #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
> >       }