This patch implements restoring of the correct rip, rsp, and rax after the svm emulation in KVM injected a selective_cr0 write intercept into the guest hypervisor. The problem was that the vmexit is emulated in the instruction emulation which later commits the registers right after the write-cr0 instruction. So the l1 guest will continue to run with the l2 rip, rsp and rax resulting in unpredictable behavior. This patch is not the final word, it is just an easy patch to fix the issue. The real fix will be done when the instruction emulator is made aware of nested virtualization. Until this is done this patch fixes the issue and provides an easy way to fix this in -stable too. Cc: stable@xxxxxxxxxx Signed-off-by: Joerg Roedel <joerg.roedel@xxxxxxx> --- arch/x86/kvm/svm.c | 33 +++++++++++++++++++++++++++++++-- 1 files changed, 31 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 55743ab..ecd4e58 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -88,6 +88,14 @@ struct nested_state { /* A VMEXIT is required but not yet emulated */ bool exit_required; + /* + * If we vmexit during an instruction emulation we need this to restore + * the l1 guest rip after the emulation + */ + unsigned long vmexit_rip; + unsigned long vmexit_rsp; + unsigned long vmexit_rax; + /* cache for intercepts of the guest */ u16 intercept_cr_read; u16 intercept_cr_write; @@ -1213,8 +1221,12 @@ static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0) if (old == new) { /* cr0 write with ts and mp unchanged */ svm->vmcb->control.exit_code = SVM_EXIT_CR0_SEL_WRITE; - if (nested_svm_exit_handled(svm) == NESTED_EXIT_DONE) + if (nested_svm_exit_handled(svm) == NESTED_EXIT_DONE) { + svm->nested.vmexit_rip = kvm_rip_read(vcpu); + svm->nested.vmexit_rsp = kvm_register_read(vcpu, VCPU_REGS_RSP); + svm->nested.vmexit_rax = kvm_register_read(vcpu, VCPU_REGS_RAX); return; + } } } @@ -2430,6 +2442,23 @@ static int emulate_on_interception(struct vcpu_svm *svm) return emulate_instruction(&svm->vcpu, 0, 0, 0) == EMULATE_DONE; } +static int cr0_write_interception(struct vcpu_svm *svm) +{ + struct kvm_vcpu *vcpu = &svm->vcpu; + int r; + + r = emulate_instruction(&svm->vcpu, 0, 0, 0); + + if (svm->nested.vmexit_rip) { + kvm_register_write(vcpu, VCPU_REGS_RIP, svm->nested.vmexit_rip); + kvm_register_write(vcpu, VCPU_REGS_RSP, svm->nested.vmexit_rsp); + kvm_register_write(vcpu, VCPU_REGS_RAX, svm->nested.vmexit_rax); + svm->nested.vmexit_rip = 0; + } + + return r == EMULATE_DONE; +} + static int cr8_write_interception(struct vcpu_svm *svm) { struct kvm_run *kvm_run = svm->vcpu.run; @@ -2692,7 +2721,7 @@ static int (*svm_exit_handlers[])(struct vcpu_svm *svm) = { [SVM_EXIT_READ_CR4] = emulate_on_interception, [SVM_EXIT_READ_CR8] = emulate_on_interception, [SVM_EXIT_CR0_SEL_WRITE] = emulate_on_interception, - [SVM_EXIT_WRITE_CR0] = emulate_on_interception, + [SVM_EXIT_WRITE_CR0] = cr0_write_interception, [SVM_EXIT_WRITE_CR3] = emulate_on_interception, [SVM_EXIT_WRITE_CR4] = emulate_on_interception, [SVM_EXIT_WRITE_CR8] = cr8_write_interception, -- 1.7.0.4 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html