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KVM: x86: Use different callback if msr access comes from the emulator

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If msr access triggers an exit to userspace, the
complete_userspace_io callback would skip instruction by vendor
callback for kvm_skip_emulated_instruction(). However, when msr
access comes from the emulator, e.g. if kvm.force_emulation_prefix
is enabled and the guest uses rdmsr/wrmsr with kvm prefix,
VM_EXIT_INSTRUCTION_LEN in vmcs is invalid and
kvm_emulate_instruction() should be used to skip instruction
instead.

As Sean noted, unlike the previous case, there's no #UD if
unrestricted guest is disabled and the guest accesses an MSR in
Big RM. So the correct way to fix this is to attach a different
callback when the msr access comes from the emulator.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong93@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <34208da8f51580a06e45afefac95afea0e3f96e3.1635842679.git.houwenlong93@linux.alibaba.com>
This commit is contained in:
Hou Wenlong 2021-11-02 17:15:31 +08:00 committed by Paolo Bonzini
parent 906fa90416
commit d2f7d49826
1 changed files with 50 additions and 37 deletions
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87
arch/x86/kvm/x86.c
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@ -118,6 +118,7 @@ static void enter_smm(struct kvm_vcpu *vcpu);
static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
static void store_regs(struct kvm_vcpu *vcpu);
static int sync_regs(struct kvm_vcpu *vcpu);
static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu);
static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
@ -710,6 +711,17 @@ int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err)
}
EXPORT_SYMBOL_GPL(kvm_complete_insn_gp);
static int complete_emulated_insn_gp(struct kvm_vcpu *vcpu, int err)
{
if (err) {
kvm_inject_gp(vcpu, 0);
return 1;
}
return kvm_emulate_instruction(vcpu, EMULTYPE_NO_DECODE | EMULTYPE_SKIP |
EMULTYPE_COMPLETE_USER_EXIT);
}
void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
{
++vcpu->stat.pf_guest;
@ -1815,22 +1827,36 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data)
}
EXPORT_SYMBOL_GPL(kvm_set_msr);
static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu)
static void complete_userspace_rdmsr(struct kvm_vcpu *vcpu)
{
int err = vcpu->run->msr.error;
if (!err) {
if (!vcpu->run->msr.error) {
kvm_rax_write(vcpu, (u32)vcpu->run->msr.data);
kvm_rdx_write(vcpu, vcpu->run->msr.data >> 32);
}
return static_call(kvm_x86_complete_emulated_msr)(vcpu, err);
}
static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu)
static int complete_emulated_msr_access(struct kvm_vcpu *vcpu)
{
return complete_emulated_insn_gp(vcpu, vcpu->run->msr.error);
}
static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu)
{
complete_userspace_rdmsr(vcpu);
return complete_emulated_msr_access(vcpu);
}
static int complete_fast_msr_access(struct kvm_vcpu *vcpu)
{
return static_call(kvm_x86_complete_emulated_msr)(vcpu, vcpu->run->msr.error);
}
static int complete_fast_rdmsr(struct kvm_vcpu *vcpu)
{
complete_userspace_rdmsr(vcpu);
return complete_fast_msr_access(vcpu);
}
static u64 kvm_msr_reason(int r)
{
switch (r) {
@ -1865,18 +1891,6 @@ static int kvm_msr_user_space(struct kvm_vcpu *vcpu, u32 index,
return 1;
}
static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index, int r)
{
return kvm_msr_user_space(vcpu, index, KVM_EXIT_X86_RDMSR, 0,
complete_emulated_rdmsr, r);
}
static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data, int r)
{
return kvm_msr_user_space(vcpu, index, KVM_EXIT_X86_WRMSR, data,
complete_emulated_wrmsr, r);
}
int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
{
u32 ecx = kvm_rcx_read(vcpu);
@ -1885,18 +1899,16 @@ int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
r = kvm_get_msr(vcpu, ecx, &data);
/* MSR read failed? See if we should ask user space */
if (r && kvm_get_msr_user_space(vcpu, ecx, r)) {
/* Bounce to user space */
return 0;
}
if (!r) {
trace_kvm_msr_read(ecx, data);
kvm_rax_write(vcpu, data & -1u);
kvm_rdx_write(vcpu, (data >> 32) & -1u);
} else {
/* MSR read failed? See if we should ask user space */
if (kvm_msr_user_space(vcpu, ecx, KVM_EXIT_X86_RDMSR, 0,
complete_fast_rdmsr, r))
return 0;
trace_kvm_msr_read_ex(ecx);
}
@ -1912,19 +1924,18 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
r = kvm_set_msr(vcpu, ecx, data);
/* MSR write failed? See if we should ask user space */
if (r && kvm_set_msr_user_space(vcpu, ecx, data, r))
/* Bounce to user space */
return 0;
/* Signal all other negative errors to userspace */
if (r < 0)
return r;
if (!r)
if (!r) {
trace_kvm_msr_write(ecx, data);
else
} else {
/* MSR write failed? See if we should ask user space */
if (kvm_msr_user_space(vcpu, ecx, KVM_EXIT_X86_WRMSR, data,
complete_fast_msr_access, r))
return 0;
/* Signal all other negative errors to userspace */
if (r < 0)
return r;
trace_kvm_msr_write_ex(ecx, data);
}
return static_call(kvm_x86_complete_emulated_msr)(vcpu, r);
}
@ -7400,7 +7411,8 @@ static int emulator_get_msr(struct x86_emulate_ctxt *ctxt,
r = kvm_get_msr(vcpu, msr_index, pdata);
if (r && kvm_get_msr_user_space(vcpu, msr_index, r)) {
if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0,
complete_emulated_rdmsr, r)) {
/* Bounce to user space */
return X86EMUL_IO_NEEDED;
}
@ -7416,7 +7428,8 @@ static int emulator_set_msr(struct x86_emulate_ctxt *ctxt,
r = kvm_set_msr(vcpu, msr_index, data);
if (r && kvm_set_msr_user_space(vcpu, msr_index, data, r)) {
if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_WRMSR, data,
complete_emulated_msr_access, r)) {
/* Bounce to user space */
return X86EMUL_IO_NEEDED;
}