From 50b2d49bafa16e6311ab2da82f5aafc5f9ada99b Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 24 Aug 2022 03:30:57 +0000 Subject: [PATCH] KVM: x86: Inject #UD on emulated XSETBV if XSAVES isn't enabled Inject #UD when emulating XSETBV if CR4.OSXSAVE is not set. This also covers the "XSAVE not supported" check, as setting CR4.OSXSAVE=1 #GPs if XSAVE is not supported (and userspace gets to keep the pieces if it forces incoherent vCPU state). Add a comment to kvm_emulate_xsetbv() to call out that the CPU checks CR4.OSXSAVE before checking for intercepts. AMD'S APM implies that #UD has priority (says that intercepts are checked before #GP exceptions), while Intel's SDM says nothing about interception priority. However, testing on hardware shows that both AMD and Intel CPUs prioritize the #UD over interception. Fixes: 02d4160fbd76 ("x86: KVM: add xsetbv to the emulator") Cc: stable@vger.kernel.org Cc: Vitaly Kuznetsov Signed-off-by: Sean Christopherson Message-Id: <20220824033057.3576315-4-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/emulate.c | 3 +++ arch/x86/kvm/x86.c | 1 + 2 files changed, 4 insertions(+) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index d5ec3a2ed5a4..aacb28c83e43 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4132,6 +4132,9 @@ static int em_xsetbv(struct x86_emulate_ctxt *ctxt) { u32 eax, ecx, edx; + if (!(ctxt->ops->get_cr(ctxt, 4) & X86_CR4_OSXSAVE)) + return emulate_ud(ctxt); + eax = reg_read(ctxt, VCPU_REGS_RAX); edx = reg_read(ctxt, VCPU_REGS_RDX); ecx = reg_read(ctxt, VCPU_REGS_RCX); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c95cf18a796c..b0c47b41c264 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1065,6 +1065,7 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr) int kvm_emulate_xsetbv(struct kvm_vcpu *vcpu) { + /* Note, #UD due to CR4.OSXSAVE=0 has priority over the intercept. */ if (static_call(kvm_x86_get_cpl)(vcpu) != 0 || __kvm_set_xcr(vcpu, kvm_rcx_read(vcpu), kvm_read_edx_eax(vcpu))) { kvm_inject_gp(vcpu, 0); -- 2.34.1