[PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

Wei Huang
2021-01-12T06:38:27Z

From: Bandan Das <bsd@redhat.com>

While running VM related instructions (VMRUN/VMSAVE/VMLOAD), some AMD
CPUs check EAX against reserved memory regions (e.g. SMM memory on host)
before checking VMCB's instruction intercept. If EAX falls into such
memory areas, #GP is triggered before VMEXIT. This causes problem under
nested virtualization. To solve this problem, KVM needs to trap #GP and
check the instructions triggering #GP. For VM execution instructions,
KVM emulates these instructions; otherwise it re-injects #GP back to
guest VMs.

Signed-off-by: Bandan Das <bsd@redhat.com>
Co-developed-by: Wei Huang <wei.huang2@amd.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
---
arch/x86/include/asm/kvm_host.h | 8 +-
arch/x86/kvm/mmu.h | 1 +
arch/x86/kvm/mmu/mmu.c | 7 ++
arch/x86/kvm/svm/svm.c | 157 +++++++++++++++++++-------------
arch/x86/kvm/svm/svm.h | 8 ++
arch/x86/kvm/vmx/vmx.c | 2 +-
arch/x86/kvm/x86.c | 37 +++++++-
7 files changed, 146 insertions(+), 74 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3d6616f6f6ef..0ddc309f5a14 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1450,10 +1450,12 @@ extern u64 kvm_mce_cap_supported;
* due to an intercepted #UD (see EMULTYPE_TRAP_UD).
* Used to test the full emulator from userspace.
*
- * EMULTYPE_VMWARE_GP - Set when emulating an intercepted #GP for VMware
+ * EMULTYPE_PARAVIRT_GP - Set when emulating an intercepted #GP for VMware
* backdoor emulation, which is opt in via module param.
* VMware backoor emulation handles select instructions
- * and reinjects the #GP for all other cases.
+ * and reinjects #GP for all other cases. This also
+ * handles other cases where #GP condition needs to be
+ * handled and emulated appropriately
*
* EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, in which
* case the CR2/GPA value pass on the stack is valid.
@@ -1463,7 +1465,7 @@ extern u64 kvm_mce_cap_supported;
#define EMULTYPE_SKIP (1 << 2)
#define EMULTYPE_ALLOW_RETRY_PF (1 << 3)
#define EMULTYPE_TRAP_UD_FORCED (1 << 4)
-#define EMULTYPE_VMWARE_GP (1 << 5)
+#define EMULTYPE_PARAVIRT_GP (1 << 5)
#define EMULTYPE_PF (1 << 6)

int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 581925e476d6..1a2fff4e7140 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -219,5 +219,6 @@ int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);

int kvm_mmu_post_init_vm(struct kvm *kvm);
void kvm_mmu_pre_destroy_vm(struct kvm *kvm);
+bool kvm_is_host_reserved_region(u64 gpa);

#endif
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6d16481aa29d..c5c4aaf01a1a 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -50,6 +50,7 @@
#include <asm/io.h>
#include <asm/vmx.h>
#include <asm/kvm_page_track.h>
+#include <asm/e820/api.h>
#include "trace.h"

extern bool itlb_multihit_kvm_mitigation;
@@ -5675,6 +5676,12 @@ void kvm_mmu_slot_set_dirty(struct kvm *kvm,
}
EXPORT_SYMBOL_GPL(kvm_mmu_slot_set_dirty);

+bool kvm_is_host_reserved_region(u64 gpa)
+{
+ return e820__mapped_raw_any(gpa-1, gpa+1, E820_TYPE_RESERVED);
+}
+EXPORT_SYMBOL_GPL(kvm_is_host_reserved_region);
+
void kvm_mmu_zap_all(struct kvm *kvm)
{
struct kvm_mmu_page *sp, *node;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7ef171790d02..74620d32aa82 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -288,6 +288,7 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
if (!(efer & EFER_SVME)) {
svm_leave_nested(svm);
svm_set_gif(svm, true);
+ clr_exception_intercept(svm, GP_VECTOR);

/*
* Free the nested guest state, unless we are in SMM.
@@ -309,6 +310,10 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)

svm->vmcb->save.efer = efer | EFER_SVME;
vmcb_mark_dirty(svm->vmcb, VMCB_CR);
+ /* Enable GP interception for SVM instructions if needed */
+ if (efer & EFER_SVME)
+ set_exception_intercept(svm, GP_VECTOR);
+
return 0;
}

@@ -1957,22 +1962,104 @@ static int ac_interception(struct vcpu_svm *svm)
return 1;
}

+static int vmload_interception(struct vcpu_svm *svm)
+{
+ struct vmcb *nested_vmcb;
+ struct kvm_host_map map;
+ int ret;
+
+ if (nested_svm_check_permissions(svm))
+ return 1;
+
+ ret = kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
+ if (ret) {
+ if (ret == -EINVAL)
+ kvm_inject_gp(&svm->vcpu, 0);
+ return 1;
+ }
+
+ nested_vmcb = map.hva;
+
+ ret = kvm_skip_emulated_instruction(&svm->vcpu);
+
+ nested_svm_vmloadsave(nested_vmcb, svm->vmcb);
+ kvm_vcpu_unmap(&svm->vcpu, &map, true);
+
+ return ret;
+}
+
+static int vmsave_interception(struct vcpu_svm *svm)
+{
+ struct vmcb *nested_vmcb;
+ struct kvm_host_map map;
+ int ret;
+
+ if (nested_svm_check_permissions(svm))
+ return 1;
+
+ ret = kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
+ if (ret) {
+ if (ret == -EINVAL)
+ kvm_inject_gp(&svm->vcpu, 0);
+ return 1;
+ }
+
+ nested_vmcb = map.hva;
+
+ ret = kvm_skip_emulated_instruction(&svm->vcpu);
+
+ nested_svm_vmloadsave(svm->vmcb, nested_vmcb);
+ kvm_vcpu_unmap(&svm->vcpu, &map, true);
+
+ return ret;
+}
+
+static int vmrun_interception(struct vcpu_svm *svm)
+{
+ if (nested_svm_check_permissions(svm))
+ return 1;
+
+ return nested_svm_vmrun(svm);
+}
+
+/* Emulate SVM VM execution instructions */
+static int svm_emulate_vm_instr(struct kvm_vcpu *vcpu, u8 modrm)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ switch (modrm) {
+ case 0xd8: /* VMRUN */
+ return vmrun_interception(svm);
+ case 0xda: /* VMLOAD */
+ return vmload_interception(svm);
+ case 0xdb: /* VMSAVE */
+ return vmsave_interception(svm);
+ default:
+ /* inject a #GP for all other cases */
+ kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
+ return 1;
+ }
+}
+
static int gp_interception(struct vcpu_svm *svm)
{
struct kvm_vcpu *vcpu = &svm->vcpu;
u32 error_code = svm->vmcb->control.exit_info_1;
-
- WARN_ON_ONCE(!enable_vmware_backdoor);
+ int rc;

/*
- * VMware backdoor emulation on #GP interception only handles IN{S},
- * OUT{S}, and RDPMC, none of which generate a non-zero error code.
+ * Only VMware backdoor and SVM VME errata are handled. Neither of
+ * them has non-zero error codes.
*/
if (error_code) {
kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
return 1;
}
- return kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE_GP);
+
+ rc = kvm_emulate_instruction(vcpu, EMULTYPE_PARAVIRT_GP);
+ if (rc > 1)
+ rc = svm_emulate_vm_instr(vcpu, rc);
+ return rc;
}

static bool is_erratum_383(void)
@@ -2113,66 +2200,6 @@ static int vmmcall_interception(struct vcpu_svm *svm)
return kvm_emulate_hypercall(&svm->vcpu);
}

-static int vmload_interception(struct vcpu_svm *svm)
-{
- struct vmcb *nested_vmcb;
- struct kvm_host_map map;
- int ret;
-
- if (nested_svm_check_permissions(svm))
- return 1;
-
- ret = kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
- if (ret) {
- if (ret == -EINVAL)
- kvm_inject_gp(&svm->vcpu, 0);
- return 1;
- }
-
- nested_vmcb = map.hva;
-
- ret = kvm_skip_emulated_instruction(&svm->vcpu);
-
- nested_svm_vmloadsave(nested_vmcb, svm->vmcb);
- kvm_vcpu_unmap(&svm->vcpu, &map, true);
-
- return ret;
-}
-
-static int vmsave_interception(struct vcpu_svm *svm)
-{
- struct vmcb *nested_vmcb;
- struct kvm_host_map map;
- int ret;
-
- if (nested_svm_check_permissions(svm))
- return 1;
-
- ret = kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
- if (ret) {
- if (ret == -EINVAL)
- kvm_inject_gp(&svm->vcpu, 0);
- return 1;
- }
-
- nested_vmcb = map.hva;
-
- ret = kvm_skip_emulated_instruction(&svm->vcpu);
-
- nested_svm_vmloadsave(svm->vmcb, nested_vmcb);
- kvm_vcpu_unmap(&svm->vcpu, &map, true);
-
- return ret;
-}
-
-static int vmrun_interception(struct vcpu_svm *svm)
-{
- if (nested_svm_check_permissions(svm))
- return 1;
-
- return nested_svm_vmrun(svm);
-}
-
void svm_set_gif(struct vcpu_svm *svm, bool value)
{
if (value) {
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 0fe874ae5498..d5dffcf59afa 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -350,6 +350,14 @@ static inline void clr_exception_intercept(struct vcpu_svm *svm, u32 bit)
recalc_intercepts(svm);
}

+static inline bool is_exception_intercept(struct vcpu_svm *svm, u32 bit)
+{
+ struct vmcb *vmcb = get_host_vmcb(svm);
+
+ WARN_ON_ONCE(bit >= 32);
+ return vmcb_is_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit);
+}
+
static inline void svm_set_intercept(struct vcpu_svm *svm, int bit)
{
struct vmcb *vmcb = get_host_vmcb(svm);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2af05d3b0590..5fac2f7cba24 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4774,7 +4774,7 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
return 1;
}
- return kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE_GP);
+ return kvm_emulate_instruction(vcpu, EMULTYPE_PARAVIRT_GP);
}

/*
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9a8969a6dd06..c3662fc3b1bc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7014,7 +7014,7 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
++vcpu->stat.insn_emulation_fail;
trace_kvm_emulate_insn_failed(vcpu);

- if (emulation_type & EMULTYPE_VMWARE_GP) {
+ if (emulation_type & EMULTYPE_PARAVIRT_GP) {
kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
return 1;
}
@@ -7267,6 +7267,28 @@ static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
return false;
}

+static int is_vm_instr_opcode(struct x86_emulate_ctxt *ctxt)
+{
+ unsigned long rax;
+
+ if (ctxt->b != 0x1)
+ return 0;
+
+ switch (ctxt->modrm) {
+ case 0xd8: /* VMRUN */
+ case 0xda: /* VMLOAD */
+ case 0xdb: /* VMSAVE */
+ rax = kvm_register_read(emul_to_vcpu(ctxt), VCPU_REGS_RAX);
+ if (!kvm_is_host_reserved_region(rax))
+ return 0;
+ break;
+ default:
+ return 0;
+ }
+
+ return ctxt->modrm;
+}
+
static bool is_vmware_backdoor_opcode(struct x86_emulate_ctxt *ctxt)
{
switch (ctxt->opcode_len) {
@@ -7305,6 +7327,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
bool writeback = true;
bool write_fault_to_spt;
+ int vminstr;

if (unlikely(!kvm_x86_ops.can_emulate_instruction(vcpu, insn, insn_len)))
return 1;
@@ -7367,10 +7390,14 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
}
}

- if ((emulation_type & EMULTYPE_VMWARE_GP) &&
- !is_vmware_backdoor_opcode(ctxt)) {
- kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
- return 1;
+ if (emulation_type & EMULTYPE_PARAVIRT_GP) {
+ vminstr = is_vm_instr_opcode(ctxt);
+ if (!vminstr && !is_vmware_backdoor_opcode(ctxt)) {
+ kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
+ return 1;
+ }
+ if (vminstr)
+ return vminstr;
}

/*
--
2.27.0