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authorSean Christopherson <sean.j.christopherson@intel.com>2019-04-02 08:10:48 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2019-04-16 15:37:38 +0200
commitb68f3cc7d978943fcf85148165b00594c38db776 (patch)
tree67a64244ef7df43f32fdd32f4264d17aef1b6be2 /arch
parent8f4dc2e77cdfaf7e644ef29693fa229db29ee1de (diff)
KVM: x86: Always use 32-bit SMRAM save state for 32-bit kernels
Invoking the 64-bit variation on a 32-bit kenrel will crash the guest, trigger a WARN, and/or lead to a buffer overrun in the host, e.g. rsm_load_state_64() writes r8-r15 unconditionally, but enum kvm_reg and thus x86_emulate_ctxt._regs only define r8-r15 for CONFIG_X86_64. KVM allows userspace to report long mode support via CPUID, even though the guest is all but guaranteed to crash if it actually tries to enable long mode. But, a pure 32-bit guest that is ignorant of long mode will happily plod along. SMM complicates things as 64-bit CPUs use a different SMRAM save state area. KVM handles this correctly for 64-bit kernels, e.g. uses the legacy save state map if userspace has hid long mode from the guest, but doesn't fare well when userspace reports long mode support on a 32-bit host kernel (32-bit KVM doesn't support 64-bit guests). Since the alternative is to crash the guest, e.g. by not loading state or explicitly requesting shutdown, unconditionally use the legacy SMRAM save state map for 32-bit KVM. If a guest has managed to get far enough to handle SMIs when running under a weird/buggy userspace hypervisor, then don't deliberately crash the guest since there are no downsides (from KVM's perspective) to allow it to continue running. Fixes: 660a5d517aaab ("KVM: x86: save/load state on SMM switch") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/emulate.c10
-rw-r--r--arch/x86/kvm/x86.c10
2 files changed, 16 insertions, 4 deletions
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f3284827c432..d0d5dd44b4f4 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2331,12 +2331,16 @@ static int em_lseg(struct x86_emulate_ctxt *ctxt)
static int emulator_has_longmode(struct x86_emulate_ctxt *ctxt)
{
+#ifdef CONFIG_X86_64
u32 eax, ebx, ecx, edx;
eax = 0x80000001;
ecx = 0;
ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, false);
return edx & bit(X86_FEATURE_LM);
+#else
+ return false;
+#endif
}
static void rsm_set_desc_flags(struct desc_struct *desc, u32 flags)
@@ -2372,6 +2376,7 @@ static int rsm_load_seg_32(struct x86_emulate_ctxt *ctxt, const char *smstate,
return X86EMUL_CONTINUE;
}
+#ifdef CONFIG_X86_64
static int rsm_load_seg_64(struct x86_emulate_ctxt *ctxt, const char *smstate,
int n)
{
@@ -2391,6 +2396,7 @@ static int rsm_load_seg_64(struct x86_emulate_ctxt *ctxt, const char *smstate,
ctxt->ops->set_segment(ctxt, selector, &desc, base3, n);
return X86EMUL_CONTINUE;
}
+#endif
static int rsm_enter_protected_mode(struct x86_emulate_ctxt *ctxt,
u64 cr0, u64 cr3, u64 cr4)
@@ -2492,6 +2498,7 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt,
return rsm_enter_protected_mode(ctxt, cr0, cr3, cr4);
}
+#ifdef CONFIG_X86_64
static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
const char *smstate)
{
@@ -2554,6 +2561,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
return X86EMUL_CONTINUE;
}
+#endif
static int em_rsm(struct x86_emulate_ctxt *ctxt)
{
@@ -2621,9 +2629,11 @@ static int em_rsm(struct x86_emulate_ctxt *ctxt)
if (ctxt->ops->pre_leave_smm(ctxt, buf))
return X86EMUL_UNHANDLEABLE;
+#ifdef CONFIG_X86_64
if (emulator_has_longmode(ctxt))
ret = rsm_load_state_64(ctxt, buf);
else
+#endif
ret = rsm_load_state_32(ctxt, buf);
if (ret != X86EMUL_CONTINUE) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 472bbbbe153a..f10fef561573 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7441,9 +7441,9 @@ static void enter_smm_save_state_32(struct kvm_vcpu *vcpu, char *buf)
put_smstate(u32, buf, 0x7ef8, vcpu->arch.smbase);
}
+#ifdef CONFIG_X86_64
static void enter_smm_save_state_64(struct kvm_vcpu *vcpu, char *buf)
{
-#ifdef CONFIG_X86_64
struct desc_ptr dt;
struct kvm_segment seg;
unsigned long val;
@@ -7493,10 +7493,8 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu, char *buf)
for (i = 0; i < 6; i++)
enter_smm_save_seg_64(vcpu, buf, i);
-#else
- WARN_ON_ONCE(1);
-#endif
}
+#endif
static void enter_smm(struct kvm_vcpu *vcpu)
{
@@ -7507,9 +7505,11 @@ static void enter_smm(struct kvm_vcpu *vcpu)
trace_kvm_enter_smm(vcpu->vcpu_id, vcpu->arch.smbase, true);
memset(buf, 0, 512);
+#ifdef CONFIG_X86_64
if (guest_cpuid_has(vcpu, X86_FEATURE_LM))
enter_smm_save_state_64(vcpu, buf);
else
+#endif
enter_smm_save_state_32(vcpu, buf);
/*
@@ -7567,8 +7567,10 @@ static void enter_smm(struct kvm_vcpu *vcpu)
kvm_set_segment(vcpu, &ds, VCPU_SREG_GS);
kvm_set_segment(vcpu, &ds, VCPU_SREG_SS);
+#ifdef CONFIG_X86_64
if (guest_cpuid_has(vcpu, X86_FEATURE_LM))
kvm_x86_ops->set_efer(vcpu, 0);
+#endif
kvm_update_cpuid(vcpu);
kvm_mmu_reset_context(vcpu);