Commit cc4cb017 authored by Maxim Levitsky's avatar Maxim Levitsky Committed by Paolo Bonzini
Browse files

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



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: default avatarQian Cai <cai@redhat.com>
Signed-off-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201101115523.115780-1-mlevitsk@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 177158e5

arch/x86/kvm/x86.c

+15 −13
Original line number Original line Diff line number Diff line
@@ -255,10 +255,9 @@ static struct kmem_cache *x86_emulator_cache; 




/*

/*

 * When called, it means the previous get/set msr reached an invalid msr.

 * 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

 * Return true if we want to ignore/silent this failed msr access.

 * to fail the caller.

 */

 */

static int kvm_msr_ignored_check(struct kvm_vcpu *vcpu, u32 msr,

static bool kvm_msr_ignored_check(struct kvm_vcpu *vcpu, u32 msr,

				  u64 data, bool write)

				  u64 data, bool write)

{

{

	const char *op = write ? "wrmsr" : "rdmsr";

	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",

			kvm_pr_unimpl("ignored %s: 0x%x data 0x%llx\n",

				      op, msr, data);

				      op, msr, data);

		/* Mask the error */

		/* Mask the error */

		return 0;

		return true;

	} else {

	} else {

		kvm_debug_ratelimited("unhandled %s: 0x%x data 0x%llx\n",

		kvm_debug_ratelimited("unhandled %s: 0x%x data 0x%llx\n",

				      op, msr, data);

				      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) {

	if (r == KVM_MSR_RET_INVALID) {

		/* Unconditionally clear the output for simplicity */

		/* Unconditionally clear the output for simplicity */

		*data = 0;

		*data = 0;

		r = kvm_msr_ignored_check(vcpu, index, 0, false);

		if (kvm_msr_ignored_check(vcpu, index, 0, false))

			r = 0;

	}

	}





	if (r)

	if (r)
@@ -1540,7 +1540,7 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data, 
	struct msr_data msr;

	struct msr_data msr;





	if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_WRITE))

	if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_WRITE))

		return -EPERM;

		return KVM_MSR_RET_FILTERED;





	switch (index) {

	switch (index) {

	case MSR_FS_BASE:

	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);

	int ret = __kvm_set_msr(vcpu, index, data, host_initiated);





	if (ret == KVM_MSR_RET_INVALID)

	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;

	return ret;

}

}
@@ -1599,7 +1600,7 @@ int __kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data, 
	int ret;

	int ret;





	if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_READ))

	if (!host_initiated && !kvm_msr_allowed(vcpu, index, KVM_MSR_FILTER_READ))

		return -EPERM;

		return KVM_MSR_RET_FILTERED;





	msr.index = index;

	msr.index = index;

	msr.host_initiated = host_initiated;

	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) {

	if (ret == KVM_MSR_RET_INVALID) {

		/* Unconditionally clear *data for simplicity */

		/* Unconditionally clear *data for simplicity */

		*data = 0;

		*data = 0;

		ret = kvm_msr_ignored_check(vcpu, index, 0, false);

		if (kvm_msr_ignored_check(vcpu, index, 0, false))

			ret = 0;

	}

	}





	return ret;

	return ret;
@@ -1662,9 +1664,9 @@ static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu) 
static u64 kvm_msr_reason(int r)

static u64 kvm_msr_reason(int r)

{

{

	switch (r) {

	switch (r) {

	case -ENOENT:

	case KVM_MSR_RET_INVALID:

		return KVM_MSR_EXIT_REASON_UNKNOWN;

		return KVM_MSR_EXIT_REASON_UNKNOWN;

	case -EPERM:

	case KVM_MSR_RET_FILTERED:

		return KVM_MSR_EXIT_REASON_FILTER;

		return KVM_MSR_EXIT_REASON_FILTER;

	default:

	default:

		return KVM_MSR_EXIT_REASON_INVAL;

		return KVM_MSR_EXIT_REASON_INVAL;

arch/x86/kvm/x86.h

+7 −1
Original line number Original line Diff line number Diff line
@@ -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);

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);

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)             \

#define __cr4_reserved_bits(__cpu_has, __c)             \

({                                                      \

({                                                      \