From: Sean Christopherson sean.j.christopherson@intel.com
[ Upstream commit b68f3cc7d978943fcf85148165b00594c38db776 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kvm/emulate.c | 10 ++++++++++ arch/x86/kvm/x86.c | 10 ++++++---- 2 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 4a688ef9e4481..429728b35bca1 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 }
#define GET_SMSTATE(type, smbase, offset) \ @@ -2381,6 +2385,7 @@ static int rsm_load_seg_32(struct x86_emulate_ctxt *ctxt, u64 smbase, int n) return X86EMUL_CONTINUE; }
+#ifdef CONFIG_X86_64 static int rsm_load_seg_64(struct x86_emulate_ctxt *ctxt, u64 smbase, int n) { struct desc_struct desc; @@ -2399,6 +2404,7 @@ static int rsm_load_seg_64(struct x86_emulate_ctxt *ctxt, u64 smbase, int n) 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) @@ -2499,6 +2505,7 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt, u64 smbase) return rsm_enter_protected_mode(ctxt, cr0, cr3, cr4); }
+#ifdef CONFIG_X86_64 static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt, u64 smbase) { struct desc_struct desc; @@ -2560,6 +2567,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt, u64 smbase)
return X86EMUL_CONTINUE; } +#endif
static int em_rsm(struct x86_emulate_ctxt *ctxt) { @@ -2616,9 +2624,11 @@ static int em_rsm(struct x86_emulate_ctxt *ctxt) if (ctxt->ops->pre_leave_smm(ctxt, smbase)) return X86EMUL_UNHANDLEABLE;
+#ifdef CONFIG_X86_64 if (emulator_has_longmode(ctxt)) ret = rsm_load_state_64(ctxt, smbase + 0x8000); else +#endif ret = rsm_load_state_32(ctxt, smbase + 0x8000);
if (ret != X86EMUL_CONTINUE) { diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 253326aaea9ac..1b80b4bd0fbf2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7226,9 +7226,9 @@ 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; @@ -7278,10 +7278,8 @@ 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) { @@ -7292,9 +7290,11 @@ 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);
/* @@ -7352,8 +7352,10 @@ 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);