Recent introduction of the userspace msr filtering added code that uses
negative error codes for cases that result in either #GP delivery to
the guest, or handled by the userspace msr filtering.
This breaks an assumption that a negative error code returned from the
msr emulation code is a semi-fatal error which should be returned
to userspace via KVM_RUN ioctl and usually kill the guest.
Fix this by reusing the already existing KVM_MSR_RET_INVALID error code,
and by adding a new KVM_MSR_RET_FILTERED error code for the
userspace filtered msrs.
Fixes: 291f35fb2c1d1 ("KVM: x86: report negative values from wrmsr emulation to userspace")
Reported-by: Qian Cai <cai@xxxxxxxxxx>
Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 29 +++++++++++++++--------------
arch/x86/kvm/x86.h | 8 +++++++-
2 files changed, 22 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 397f599b20e5a..537130d78b2af 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -255,11 +255,10 @@ static struct kmem_cache *x86_emulator_cache;
/*
* When called, it means the previous get/set msr reached an invalid msr.
- * Return 0 if we want to ignore/silent this failed msr access, or 1 if we want
- * to fail the caller.
+ * Return true if we want to ignore/silent this failed msr access.
*/
-static int kvm_msr_ignored_check(struct kvm_vcpu *vcpu, u32 msr,
- u64 data, bool write)
+static bool kvm_msr_ignored_check(struct kvm_vcpu *vcpu, u32 msr,
+ u64 data, bool write)
{
const char *op = write ? "wrmsr" : "rdmsr";
@@ -267,12 +266,11 @@ static int kvm_msr_ignored_check(struct kvm_vcpu *vcpu, u32 msr,
if (report_ignored_msrs)
vcpu_unimpl(vcpu, "ignored %s: 0x%x data 0x%llx\n",
op, msr, data);
- /* Mask the error */
- return 0;
+ return true;
} else {
vcpu_debug_ratelimited(vcpu, "unhandled %s: 0x%x data 0x%llx\n",
op, msr, data);
- return -ENOENT;
+ return false;
}
}
@@ -1416,7 +1414,8 @@ static int do_get_msr_feature(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
if (r == KVM_MSR_RET_INVALID) {
/* Unconditionally clear the output for simplicity */
*data = 0;
- r = kvm_msr_ignored_check(vcpu, index, 0, false);
+ if (kvm_msr_ignored_check(vcpu, index, 0, false))
+ r = 0;
}
if (r)
@@ -1540,7 +1539,7 @@ 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 -EPERM;
+ return KVM_MSR_RET_FILTERED;
switch (index) {
case MSR_FS_BASE:
@@ -1581,7 +1580,8 @@ static int kvm_set_msr_ignored_check(struct kvm_vcpu *vcpu,
int ret = __kvm_set_msr(vcpu, index, data, host_initiated);
if (ret == KVM_MSR_RET_INVALID)
- ret = kvm_msr_ignored_check(vcpu, index, data, true);
+ if (kvm_msr_ignored_check(vcpu, index, data, true))
+ ret = 0;
return ret;
}
@@ -1599,7 +1599,7 @@ int __kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data,
int ret;
if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_READ))
- return -EPERM;
+ return KVM_MSR_RET_FILTERED;
msr.index = index;
msr.host_initiated = host_initiated;
@@ -1618,7 +1618,8 @@ static int kvm_get_msr_ignored_check(struct kvm_vcpu *vcpu,
if (ret == KVM_MSR_RET_INVALID) {
/* Unconditionally clear *data for simplicity */
*data = 0;
- ret = kvm_msr_ignored_check(vcpu, index, 0, false);
+ if (kvm_msr_ignored_check(vcpu, index, 0, false))
+ ret = 0;
}
return ret;
@@ -1662,9 +1663,9 @@ static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu)
static u64 kvm_msr_reason(int r)
{
switch (r) {
- case -ENOENT:
+ case KVM_MSR_RET_INVALID:
return KVM_MSR_EXIT_REASON_UNKNOWN;
- case -EPERM:
+ case KVM_MSR_RET_FILTERED:
return KVM_MSR_EXIT_REASON_FILTER;
default:
return KVM_MSR_EXIT_REASON_INVAL;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 3900ab0c6004d..e7ca622a468f5 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -376,7 +376,13 @@ int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
int kvm_handle_invpcid(struct kvm_vcpu *vcpu, unsigned long type, gva_t gva);
bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
-#define KVM_MSR_RET_INVALID 2
+/*
+ * Internal error codes that are used to indicate that MSR emulation encountered
+ * an error that should result in #GP in the guest, unless userspace
+ * handles it.
+ */
+#define KVM_MSR_RET_INVALID 2 /* in-kernel MSR emulation #GP condition */
+#define KVM_MSR_RET_FILTERED 3 /* #GP due to userspace MSR filter */
#define __cr4_reserved_bits(__cpu_has, __c) \
({ \
--
2.26.2
