Messages in this thread | | | Date | Thu, 16 Jun 2022 23:56:17 +0800 | Subject | Re: [PATCH 19/19] KVM: x86: Enable supervisor IBT support for guest | From | "Yang, Weijiang" <> |
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On 6/16/2022 7:19 PM, Peter Zijlstra wrote: > On Thu, Jun 16, 2022 at 04:46:43AM -0400, Yang Weijiang wrote: >> Mainline kernel now supports supervisor IBT for kernel code, >> to make s-IBT work in guest(nested guest), pass through >> MSR_IA32_S_CET to guest(nested guest) if host kernel and KVM >> enabled IBT. Note, s-IBT can work independent to host xsaves >> support because guest MSR_IA32_S_CET can be stored/loaded from >> specific VMCS field. > >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index fe049d0e5ecc..c0118b33806a 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -1463,6 +1463,7 @@ static const u32 msrs_to_save_all[] = { >> MSR_IA32_XFD, MSR_IA32_XFD_ERR, >> MSR_IA32_XSS, >> MSR_IA32_U_CET, MSR_IA32_PL3_SSP, MSR_KVM_GUEST_SSP, >> + MSR_IA32_S_CET, >> }; > > So much like my local kvm/qemu hacks; this patch suffers the problem of > not exposing S_SHSTK. What happens if a guest tries to use that? With current solution, I think guest kernel will hit #GP while reading/writing PL0_SSP. > > Should we intercept and reject setting those bits or complete this patch > and support full S_SHSTK? (with all the warts and horrors that entails) > > I don't think throwing this out in this half-finished state makes much > sense (which is why I never much shared my hacks).
You reminded me to think over these cases even I don't have a solution now,
thank you!
> > >> @@ -11830,7 +11835,13 @@ int kvm_arch_hardware_setup(void *opaque) >> /* Update CET features now as kvm_caps.supported_xss is finalized. */ >> if (!kvm_cet_user_supported()) { >> kvm_cpu_cap_clear(X86_FEATURE_SHSTK); >> - kvm_cpu_cap_clear(X86_FEATURE_IBT); >> + /* If CET user bit is disabled due to cmdline option such as >> + * noxsaves, but kernel IBT is on, this means we can expose >> + * kernel IBT alone to guest since CET user mode msrs are not >> + * passed through to guest. >> + */ > Invalid multi-line comment style. Oops, last minute change messed it up :-( > >> + if (!cet_kernel_ibt_supported()) >> + kvm_cpu_cap_clear(X86_FEATURE_IBT);
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