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x86/fpu: Allow caller to constrain xfeatures when copying to uabi buffer

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commit 18164f66e6c59fda15c198b371fa008431efdb22 upstream.

Plumb an xfeatures mask into __copy_xstate_to_uabi_buf() so that KVM can
constrain which xfeatures are saved into the userspace buffer without
having to modify the user_xfeatures field in KVM's guest_fpu state.

KVM's ABI for KVM_GET_XSAVE{2} is that features that are not exposed to
guest must not show up in the effective xstate_bv field of the buffer.
Saving only the guest-supported xfeatures allows userspace to load the
saved state on a different host with a fewer xfeatures, so long as the
target host supports the xfeatures that are exposed to the guest.

KVM currently sets user_xfeatures directly to restrict KVM_GET_XSAVE{2} to
the set of guest-supported xfeatures, but doing so broke KVM's historical
ABI for KVM_SET_XSAVE, which allows userspace to load any xfeatures that
are supported by the *host*.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230928001956.924301-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sean Christopherson 2023-09-27 17:19:52 -07:00 committed by Greg Kroah-Hartman
parent 57d0639f60
commit 20695711e2
5 changed files with 22 additions and 19 deletions
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3
arch/x86/include/asm/fpu/api.h
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@ -148,7 +148,8 @@ static inline void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd) {
static inline void fpu_sync_guest_vmexit_xfd_state(void) { }
#endif
extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, unsigned int size, u32 pkru);
extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
unsigned int size, u64 xfeatures, u32 pkru);
extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, u64 xcr0, u32 *vpkru);
static inline void fpstate_set_confidential(struct fpu_guest *gfpu)

5
arch/x86/kernel/fpu/core.c
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@ -369,14 +369,15 @@ int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpstate);
void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
unsigned int size, u32 pkru)
unsigned int size, u64 xfeatures, u32 pkru)
{
struct fpstate *kstate = gfpu->fpstate;
union fpregs_state *ustate = buf;
struct membuf mb = { .p = buf, .left = size };
if (cpu_feature_enabled(X86_FEATURE_XSAVE)) {
__copy_xstate_to_uabi_buf(mb, kstate, pkru, XSTATE_COPY_XSAVE);
__copy_xstate_to_uabi_buf(mb, kstate, xfeatures, pkru,
XSTATE_COPY_XSAVE);
} else {
memcpy(&ustate->fxsave, &kstate->regs.fxsave,
sizeof(ustate->fxsave));

7
arch/x86/kernel/fpu/xstate.c
View File

@ -1053,6 +1053,7 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate,
* __copy_xstate_to_uabi_buf - Copy kernel saved xstate to a UABI buffer
* @to: membuf descriptor
* @fpstate: The fpstate buffer from which to copy
* @xfeatures: The mask of xfeatures to save (XSAVE mode only)
* @pkru_val: The PKRU value to store in the PKRU component
* @copy_mode: The requested copy mode
*
@ -1063,7 +1064,8 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate,
* It supports partial copy but @to.pos always starts from zero.
*/
void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
u32 pkru_val, enum xstate_copy_mode copy_mode)
u64 xfeatures, u32 pkru_val,
enum xstate_copy_mode copy_mode)
{
const unsigned int off_mxcsr = offsetof(struct fxregs_state, mxcsr);
struct xregs_state *xinit = &init_fpstate.regs.xsave;
@ -1087,7 +1089,7 @@ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
break;
case XSTATE_COPY_XSAVE:
header.xfeatures &= fpstate->user_xfeatures;
header.xfeatures &= fpstate->user_xfeatures & xfeatures;
break;
}
@ -1189,6 +1191,7 @@ void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
enum xstate_copy_mode copy_mode)
{
__copy_xstate_to_uabi_buf(to, tsk->thread.fpu.fpstate,
tsk->thread.fpu.fpstate->user_xfeatures,
tsk->thread.pkru, copy_mode);
}

3
arch/x86/kernel/fpu/xstate.h
View File

@ -43,7 +43,8 @@ enum xstate_copy_mode {
struct membuf;
extern void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
u32 pkru_val, enum xstate_copy_mode copy_mode);
u64 xfeatures, u32 pkru_val,
enum xstate_copy_mode copy_mode);
extern void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
enum xstate_copy_mode mode);
extern int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u32 *pkru);

23
arch/x86/kvm/x86.c
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@ -5301,17 +5301,6 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
return 0;
}
static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
struct kvm_xsave *guest_xsave)
{
if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
return;
fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
guest_xsave->region,
sizeof(guest_xsave->region),
vcpu->arch.pkru);
}
static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
u8 *state, unsigned int size)
@ -5319,8 +5308,16 @@ static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
return;
fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
state, size, vcpu->arch.pkru);
fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu, state, size,
vcpu->arch.guest_fpu.fpstate->user_xfeatures,
vcpu->arch.pkru);
}
static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
struct kvm_xsave *guest_xsave)
{
return kvm_vcpu_ioctl_x86_get_xsave2(vcpu, (void *)guest_xsave->region,
sizeof(guest_xsave->region));
}
static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,