Commit 18164f66 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

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



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: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20230928001956.924301-2-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 4bcd9bc6

arch/x86/include/asm/fpu/api.h

+2 −1
Original line number Diff line number Diff line
@@ -157,7 +157,8 @@ 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)

arch/x86/kernel/fpu/core.c

+3 −2
Original line number Diff line number Diff line
@@ -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));

arch/x86/kernel/fpu/xstate.c

+5 −2
Original line number Diff line number Diff line
@@ -1049,6 +1049,7 @@ 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

 *
@@ -1059,7 +1060,8 @@ 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;
@@ -1083,7 +1085,7 @@ 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;

	}
@@ -1185,6 +1187,7 @@ 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);

}

arch/x86/kernel/fpu/xstate.h

+2 −1
Original line number Diff line number Diff line
@@ -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);

arch/x86/kvm/x86.c

+9 −12
Original line number Diff line number Diff line
@@ -5382,26 +5382,23 @@ 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)



static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,

					  u8 *state, unsigned int size)

{

	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),

	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_xsave2(struct kvm_vcpu *vcpu,

					  u8 *state, unsigned int size)

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,

				       state, size, vcpu->arch.pkru);

	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,