kvm: vmx: Scrub hardware GPRs at VM-exit

Guest GPR values are live in the hardware GPRs at VM-exit.  Do not
leave any guest values in hardware GPRs after the guest GPR values are
saved to the vcpu_vmx structure.

This is a partial mitigation for CVE 2017-5715 and CVE 2017-5753.
Specifically, it defeats the Project Zero PoC for CVE 2017-5715.

Suggested-by: Eric Northup <digitaleric@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Eric Northup <digitaleric@google.com>
Reviewed-by: Benjamin Serebrin <serebrin@google.com>
Reviewed-by: Andrew Honig <ahonig@google.com>
[Paolo: Add AMD bits, Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 32 insertions, 1 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index eb714f1cdf7e..bb31c801f1fc 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4986,6 +4986,25 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
                 "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
                 :
                 : [svm]"a"(svm),
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 8eba631c4dbd..c1e7ed371259 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -9415,6 +9415,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
                 /* Save guest registers, load host registers, keep flags */
                 "mov %0, %c[wordsize](%%" _ASM_SP ") \n\t"
                 "pop %0 \n\t"
+                "setbe %c[fail](%0)\n\t"
                 "mov %%" _ASM_AX ", %c[rax](%0) \n\t"
                 "mov %%" _ASM_BX ", %c[rbx](%0) \n\t"
                 __ASM_SIZE(pop) " %c[rcx](%0) \n\t"
@@ -9431,12 +9432,23 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
                 "mov %%r13, %c[r13](%0) \n\t"
                 "mov %%r14, %c[r14](%0) \n\t"
                 "mov %%r15, %c[r15](%0) \n\t"
+                "xor %%r8d,  %%r8d \n\t"
+                "xor %%r9d,  %%r9d \n\t"
+                "xor %%r10d, %%r10d \n\t"
+                "xor %%r11d, %%r11d \n\t"
+                "xor %%r12d, %%r12d \n\t"
+                "xor %%r13d, %%r13d \n\t"
+                "xor %%r14d, %%r14d \n\t"
+                "xor %%r15d, %%r15d \n\t"
 #endif
                 "mov %%cr2, %%" _ASM_AX "   \n\t"
                 "mov %%" _ASM_AX ", %c[cr2](%0) \n\t"
 
+                "xor %%eax, %%eax \n\t"
+                "xor %%ebx, %%ebx \n\t"
+                "xor %%esi, %%esi \n\t"
+                "xor %%edi, %%edi \n\t"
                 "pop  %%" _ASM_BP "; pop  %%" _ASM_DX " \n\t"
-                "setbe %c[fail](%0) \n\t"
                 ".pushsection .rodata \n\t"
                 ".global vmx_return \n\t"
                 "vmx_return: " _ASM_PTR " 2b \n\t"