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KVM: x86: use positive error values for msr emulation that causes #GP

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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@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201101115523.115780-1-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Maxim Levitsky 2020-11-01 13:55:23 +02:00 committed by Paolo Bonzini
parent 177158e5b1
commit cc4cb01767
2 changed files with 22 additions and 14 deletions
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28
arch/x86/kvm/x86.c
View File

@ -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";
@ -268,11 +267,11 @@ static int kvm_msr_ignored_check(struct kvm_vcpu *vcpu, u32 msr,
kvm_pr_unimpl("ignored %s: 0x%x data 0x%llx\n",
op, msr, data);
/* Mask the error */
return 0;
return true;
} else {
kvm_debug_ratelimited("unhandled %s: 0x%x data 0x%llx\n",
op, msr, data);
return -ENOENT;
return false;
}
}
@ -1416,7 +1415,8 @@ 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 +1540,7 @@ 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 +1581,8 @@ 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 +1600,7 @@ 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 +1619,8 @@ 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 +1664,9 @@ 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;

8
arch/x86/kvm/x86.h
View File

@ -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) \
({ \