x86/bugs, KVM: Support the combination of guest and host IBRS

[mirror_ubuntu-artful-kernel.git] / arch / x86 / kvm / svm.c

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index fe90956bdf1ba4f043ce6494ad6990a9755b05a4..f9e7ddd56ea6e480fe41bd290884fd401c6bd93b 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -45,6 +45,7 @@
 #include <asm/debugreg.h>
 #include <asm/kvm_para.h>
 #include <asm/irq_remapping.h>
+#include <asm/nospec-branch.h>
 
 #include <asm/virtext.h>
 #include "trace.h"
@@ -4900,8 +4901,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 
        local_irq_enable();
 
-       if (ibrs_inuse && (svm->spec_ctrl != FEATURE_ENABLE_IBRS))
-               wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
+       /* SMB: Don't care about ibrs_inuse but rely on guest value */
+       x86_spec_ctrl_set_guest(svm->spec_ctrl);
 
        asm volatile (
                "push %%" _ASM_BP "; \n\t"
@@ -4946,6 +4947,25 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
                "mov %%r13, %c[r13](%[svm]) \n\t"
                "mov %%r14, %c[r14](%[svm]) \n\t"
                "mov %%r15, %c[r15](%[svm]) \n\t"
+#endif
+               /*
+               * Clear host registers marked as clobbered to prevent
+               * speculative use.
+               */
+               "xor %%" _ASM_BX ", %%" _ASM_BX " \n\t"
+               "xor %%" _ASM_CX ", %%" _ASM_CX " \n\t"
+               "xor %%" _ASM_DX ", %%" _ASM_DX " \n\t"
+               "xor %%" _ASM_SI ", %%" _ASM_SI " \n\t"
+               "xor %%" _ASM_DI ", %%" _ASM_DI " \n\t"
+#ifdef CONFIG_X86_64
+               "xor %%r8, %%r8 \n\t"
+               "xor %%r9, %%r9 \n\t"
+               "xor %%r10, %%r10 \n\t"
+               "xor %%r11, %%r11 \n\t"
+               "xor %%r12, %%r12 \n\t"
+               "xor %%r13, %%r13 \n\t"
+               "xor %%r14, %%r14 \n\t"
+               "xor %%r15, %%r15 \n\t"
 #endif
                "pop %%" _ASM_BP
                :
@@ -4976,11 +4996,10 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 #endif
                );
 
-       if (ibrs_inuse) {
-               rdmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
-               if (svm->spec_ctrl != FEATURE_ENABLE_IBRS)
-                       wrmsrl(MSR_IA32_SPEC_CTRL, FEATURE_ENABLE_IBRS);
-       }
+       /* Eliminate branch target predictions from guest mode */
+       vmexit_fill_RSB();
+
+       x86_spec_ctrl_restore_host(svm->spec_ctrl);
 
 #ifdef CONFIG_X86_64
        wrmsrl(MSR_GS_BASE, svm->host.gs_base);