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KVM: x86: Only do MSR filtering when access MSR by rdmsr/wrmsr
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If MSR access is rejected by MSR filtering,
kvm_set_msr()/kvm_get_msr() would return KVM_MSR_RET_FILTERED,
and the return value is only handled well for rdmsr/wrmsr.
However, some instruction emulation and state transition also
use kvm_set_msr()/kvm_get_msr() to do msr access but may trigger
some unexpected results if MSR access is rejected, E.g. RDPID
emulation would inject a #UD but RDPID wouldn't cause a exit
when RDPID is supported in hardware and ENABLE_RDTSCP is set.
And it would also cause failure when load MSR at nested entry/exit.
Since msr filtering is based on MSR bitmap, it is better to only
do MSR filtering for rdmsr/wrmsr.

Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Message-Id: <2b2774154f7532c96a6f04d71c82a8bec7d9e80b.1646655860.git.houwenlong.hwl@antgroup.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Hou Wenlong authored and Paolo Bonzini committed Apr 2, 2022
1 parent a836839 commit ac8d6ca
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Showing 3 changed files with 40 additions and 16 deletions.
4 changes: 2 additions & 2 deletions arch/x86/kvm/emulate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3625,7 +3625,7 @@ static int em_wrmsr(struct x86_emulate_ctxt *ctxt)

msr_data = (u32)reg_read(ctxt, VCPU_REGS_RAX)
| ((u64)reg_read(ctxt, VCPU_REGS_RDX) << 32);
r = ctxt->ops->set_msr(ctxt, msr_index, msr_data);
r = ctxt->ops->set_msr_with_filter(ctxt, msr_index, msr_data);

if (r == X86EMUL_IO_NEEDED)
return r;
Expand All @@ -3642,7 +3642,7 @@ static int em_rdmsr(struct x86_emulate_ctxt *ctxt)
u64 msr_data;
int r;

r = ctxt->ops->get_msr(ctxt, msr_index, &msr_data);
r = ctxt->ops->get_msr_with_filter(ctxt, msr_index, &msr_data);

if (r == X86EMUL_IO_NEEDED)
return r;
Expand Down
2 changes: 2 additions & 0 deletions arch/x86/kvm/kvm_emulate.h
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Original file line number Diff line number Diff line change
Expand Up @@ -210,6 +210,8 @@ struct x86_emulate_ops {
int (*set_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong value);
u64 (*get_smbase)(struct x86_emulate_ctxt *ctxt);
void (*set_smbase)(struct x86_emulate_ctxt *ctxt, u64 smbase);
int (*set_msr_with_filter)(struct x86_emulate_ctxt *ctxt, u32 msr_index, u64 data);
int (*get_msr_with_filter)(struct x86_emulate_ctxt *ctxt, u32 msr_index, u64 *pdata);
int (*set_msr)(struct x86_emulate_ctxt *ctxt, u32 msr_index, u64 data);
int (*get_msr)(struct x86_emulate_ctxt *ctxt, u32 msr_index, u64 *pdata);
int (*check_pmc)(struct x86_emulate_ctxt *ctxt, u32 pmc);
Expand Down
50 changes: 36 additions & 14 deletions arch/x86/kvm/x86.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1748,9 +1748,6 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
{
struct msr_data msr;

if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_WRITE))
return KVM_MSR_RET_FILTERED;

switch (index) {
case MSR_FS_BASE:
case MSR_GS_BASE:
Expand Down Expand Up @@ -1832,9 +1829,6 @@ int __kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data,
struct msr_data msr;
int ret;

if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_READ))
return KVM_MSR_RET_FILTERED;

switch (index) {
case MSR_TSC_AUX:
if (!kvm_is_supported_user_return_msr(MSR_TSC_AUX))
Expand Down Expand Up @@ -1871,6 +1865,20 @@ static int kvm_get_msr_ignored_check(struct kvm_vcpu *vcpu,
return ret;
}

static int kvm_get_msr_with_filter(struct kvm_vcpu *vcpu, u32 index, u64 *data)
{
if (!kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_READ))
return KVM_MSR_RET_FILTERED;
return kvm_get_msr_ignored_check(vcpu, index, data, false);
}

static int kvm_set_msr_with_filter(struct kvm_vcpu *vcpu, u32 index, u64 data)
{
if (!kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_WRITE))
return KVM_MSR_RET_FILTERED;
return kvm_set_msr_ignored_check(vcpu, index, data, false);
}

int kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data)
{
return kvm_get_msr_ignored_check(vcpu, index, data, false);
Expand Down Expand Up @@ -1953,7 +1961,7 @@ int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
u64 data;
int r;

r = kvm_get_msr(vcpu, ecx, &data);
r = kvm_get_msr_with_filter(vcpu, ecx, &data);

if (!r) {
trace_kvm_msr_read(ecx, data);
Expand All @@ -1978,7 +1986,7 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
u64 data = kvm_read_edx_eax(vcpu);
int r;

r = kvm_set_msr(vcpu, ecx, data);
r = kvm_set_msr_with_filter(vcpu, ecx, data);

if (!r) {
trace_kvm_msr_write(ecx, data);
Expand Down Expand Up @@ -7631,13 +7639,13 @@ static void emulator_set_segment(struct x86_emulate_ctxt *ctxt, u16 selector,
return;
}

static int emulator_get_msr(struct x86_emulate_ctxt *ctxt,
u32 msr_index, u64 *pdata)
static int emulator_get_msr_with_filter(struct x86_emulate_ctxt *ctxt,
u32 msr_index, u64 *pdata)
{
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
int r;

r = kvm_get_msr(vcpu, msr_index, pdata);
r = kvm_get_msr_with_filter(vcpu, msr_index, pdata);

if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0,
complete_emulated_rdmsr, r)) {
Expand All @@ -7648,13 +7656,13 @@ static int emulator_get_msr(struct x86_emulate_ctxt *ctxt,
return r;
}

static int emulator_set_msr(struct x86_emulate_ctxt *ctxt,
u32 msr_index, u64 data)
static int emulator_set_msr_with_filter(struct x86_emulate_ctxt *ctxt,
u32 msr_index, u64 data)
{
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
int r;

r = kvm_set_msr(vcpu, msr_index, data);
r = kvm_set_msr_with_filter(vcpu, msr_index, data);

if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_WRMSR, data,
complete_emulated_msr_access, r)) {
Expand All @@ -7665,6 +7673,18 @@ static int emulator_set_msr(struct x86_emulate_ctxt *ctxt,
return r;
}

static int emulator_get_msr(struct x86_emulate_ctxt *ctxt,
u32 msr_index, u64 *pdata)
{
return kvm_get_msr(emul_to_vcpu(ctxt), msr_index, pdata);
}

static int emulator_set_msr(struct x86_emulate_ctxt *ctxt,
u32 msr_index, u64 data)
{
return kvm_set_msr(emul_to_vcpu(ctxt), msr_index, data);
}

static u64 emulator_get_smbase(struct x86_emulate_ctxt *ctxt)
{
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
Expand Down Expand Up @@ -7803,6 +7823,8 @@ static const struct x86_emulate_ops emulate_ops = {
.set_dr = emulator_set_dr,
.get_smbase = emulator_get_smbase,
.set_smbase = emulator_set_smbase,
.set_msr_with_filter = emulator_set_msr_with_filter,
.get_msr_with_filter = emulator_get_msr_with_filter,
.set_msr = emulator_set_msr,
.get_msr = emulator_get_msr,
.check_pmc = emulator_check_pmc,
Expand Down

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