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

Sean Christopherson
2021-02-16T16:22:27Z

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
> }