arch/x86/kernel/fpu/signal.c - linux/kernel/git/tip/tip - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * FPU signal frame handling routines.
  */

 #include <linux/compat.h>
 #include <linux/cpu.h>
 #include <linux/pagemap.h>

 #include <asm/fpu/internal.h>
 #include <asm/fpu/signal.h>
 #include <asm/fpu/regset.h>
 #include <asm/fpu/xstate.h>

 #include <asm/sigframe.h>
 #include <asm/trace/fpu.h>

 static struct _fpx_sw_bytes fx_sw_reserved __ro_after_init;
 static struct _fpx_sw_bytes fx_sw_reserved_ia32 __ro_after_init;

 /*
  * Check for the presence of extended state information in the
  * user fpstate pointer in the sigcontext.
  */
 static inline int check_xstate_in_sigframe(struct fxregs_state __user *fxbuf,
 					   struct _fpx_sw_bytes *fx_sw)
 {
 	int min_xstate_size = sizeof(struct fxregs_state) +
 			      sizeof(struct xstate_header);
 	void __user *fpstate = fxbuf;
 	unsigned int magic2;

 	if (__copy_from_user(fx_sw, &fxbuf->sw_reserved[0], sizeof(*fx_sw)))
 		return -EFAULT;

 	/* Check for the first magic field and other error scenarios. */
 	if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
 	    fx_sw->xstate_size < min_xstate_size ||
 	    fx_sw->xstate_size > fpu_user_xstate_size ||
 	    fx_sw->xstate_size > fx_sw->extended_size)
 		goto setfx;

 	/*
 	 * Check for the presence of second magic word at the end of memory
 	 * layout. This detects the case where the user just copied the legacy
 	 * fpstate layout with out copying the extended state information
 	 * in the memory layout.
 	 */
 	if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size)))
 		return -EFAULT;

 	if (likely(magic2 == FP_XSTATE_MAGIC2))
 		return 0;
 setfx:
 	trace_x86_fpu_xstate_check_failed(&current->thread.fpu);

 	/* Set the parameters for fx only state */
 	fx_sw->magic1 = 0;
 	fx_sw->xstate_size = sizeof(struct fxregs_state);
 	fx_sw->xfeatures = XFEATURE_MASK_FPSSE;
 	return 0;
 }

 /*
  * Signal frame handlers.
  */
 static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
 {
 	if (use_fxsr()) {
 		struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
 		struct user_i387_ia32_struct env;
 		struct _fpstate_32 __user *fp = buf;

 		fpregs_lock();
 		if (!test_thread_flag(TIF_NEED_FPU_LOAD))
 			fxsave(&tsk->thread.fpu.state.fxsave);
 		fpregs_unlock();

 		convert_from_fxsr(&env, tsk);

 		if (__copy_to_user(buf, &env, sizeof(env)) ||
 		    __put_user(xsave->i387.swd, &fp->status) ||
 		    __put_user(X86_FXSR_MAGIC, &fp->magic))
 			return -1;
 	} else {
 		struct fregs_state __user *fp = buf;
 		u32 swd;
 		if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
 			return -1;
 	}

 	return 0;
 }

 static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
 {
 	struct xregs_state __user *x = buf;
 	struct _fpx_sw_bytes *sw_bytes;
 	u32 xfeatures;
 	int err;

 	/* Setup the bytes not touched by the [f]xsave and reserved for SW. */
 	sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
 	err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));

 	if (!use_xsave())
 		return err;

 	err |= __put_user(FP_XSTATE_MAGIC2,
 			  (__u32 __user *)(buf + fpu_user_xstate_size));

 	/*
 	 * Read the xfeatures which we copied (directly from the cpu or
 	 * from the state in task struct) to the user buffers.
 	 */
 	err |= __get_user(xfeatures, (__u32 __user *)&x->header.xfeatures);

 	/*
 	 * For legacy compatible, we always set FP/SSE bits in the bit
 	 * vector while saving the state to the user context. This will
 	 * enable us capturing any changes(during sigreturn) to
 	 * the FP/SSE bits by the legacy applications which don't touch
 	 * xfeatures in the xsave header.
 	 *
 	 * xsave aware apps can change the xfeatures in the xsave
 	 * header as well as change any contents in the memory layout.
 	 * xrestore as part of sigreturn will capture all the changes.
 	 */
 	xfeatures |= XFEATURE_MASK_FPSSE;

 	err |= __put_user(xfeatures, (__u32 __user *)&x->header.xfeatures);

 	return err;
 }

 static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
 {
 	int err;

 	if (use_xsave())
 		err = xsave_to_user_sigframe(buf);
 	else if (use_fxsr())
 		err = fxsave_to_user_sigframe((struct fxregs_state __user *) buf);
 	else
 		err = fnsave_to_user_sigframe((struct fregs_state __user *) buf);

 	if (unlikely(err) && __clear_user(buf, fpu_user_xstate_size))
 		err = -EFAULT;
 	return err;
 }

 /*
  * Save the fpu, extended register state to the user signal frame.
  *
  * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
  *  state is copied.
  *  'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
  *
  *	buf == buf_fx for 64-bit frames and 32-bit fsave frame.
  *	buf != buf_fx for 32-bit frames with fxstate.
  *
  * Try to save it directly to the user frame with disabled page fault handler.
  * If this fails then do the slow path where the FPU state is first saved to
  * task's fpu->state and then copy it to the user frame pointed to by the
  * aligned pointer 'buf_fx'.
  *
  * If this is a 32-bit frame with fxstate, put a fsave header before
  * the aligned state at 'buf_fx'.
  *
  * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
  * indicating the absence/presence of the extended state to the user.
  */
 int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 {
 	struct task_struct *tsk = current;
 	int ia32_fxstate = (buf != buf_fx);
 	int ret;

 	ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 			 IS_ENABLED(CONFIG_IA32_EMULATION));

 	if (!static_cpu_has(X86_FEATURE_FPU)) {
 		struct user_i387_ia32_struct fp;
 		fpregs_soft_get(current, NULL, (struct membuf){.p = &fp,
 						.left = sizeof(fp)});
 		return copy_to_user(buf, &fp, sizeof(fp)) ? -EFAULT : 0;
 	}

 	if (!access_ok(buf, size))
 		return -EACCES;
 retry:
 	/*
 	 * Load the FPU registers if they are not valid for the current task.
 	 * With a valid FPU state we can attempt to save the state directly to
 	 * userland's stack frame which will likely succeed. If it does not,
 	 * resolve the fault in the user memory and try again.
 	 */
 	fpregs_lock();
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
 		fpregs_restore_userregs();

 	pagefault_disable();
 	ret = copy_fpregs_to_sigframe(buf_fx);
 	pagefault_enable();
 	fpregs_unlock();

 	if (ret) {
 		if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
 			goto retry;
 		return -EFAULT;
 	}

 	/* Save the fsave header for the 32-bit frames. */
 	if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
 		return -1;

 	if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
 		return -1;

 	return 0;
 }

 static int __restore_fpregs_from_user(void __user *buf, u64 xrestore,
 				      bool fx_only)
 {
 	if (use_xsave()) {
 		u64 init_bv = xfeatures_mask_uabi() & ~xrestore;
 		int ret;

 		if (likely(!fx_only))
 			ret = xrstor_from_user_sigframe(buf, xrestore);
 		else
 			ret = fxrstor_from_user_sigframe(buf);

 		if (!ret && unlikely(init_bv))
 			os_xrstor(&init_fpstate.xsave, init_bv);
 		return ret;
 	} else if (use_fxsr()) {
 		return fxrstor_from_user_sigframe(buf);
 	} else {
 		return frstor_from_user_sigframe(buf);
 	}
 }

 /*
  * Attempt to restore the FPU registers directly from user memory.
  * Pagefaults are handled and any errors returned are fatal.
  */
 static int restore_fpregs_from_user(void __user *buf, u64 xrestore,
 				    bool fx_only, unsigned int size)
 {
 	struct fpu *fpu = &current->thread.fpu;
 	int ret;

 retry:
 	fpregs_lock();
 	pagefault_disable();
 	ret = __restore_fpregs_from_user(buf, xrestore, fx_only);
 	pagefault_enable();

 	if (unlikely(ret)) {
 		/*
 		 * The above did an FPU restore operation, restricted to
 		 * the user portion of the registers, and failed, but the
 		 * microcode might have modified the FPU registers
 		 * nevertheless.
 		 *
 		 * If the FPU registers do not belong to current, then
 		 * invalidate the FPU register state otherwise the task
 		 * might preempt current and return to user space with
 		 * corrupted FPU registers.
 		 */
 		if (test_thread_flag(TIF_NEED_FPU_LOAD))
 			__cpu_invalidate_fpregs_state();
 		fpregs_unlock();

 		/* Try to handle #PF, but anything else is fatal. */
 		if (ret != -EFAULT)
 			return -EINVAL;

 		ret = fault_in_pages_readable(buf, size);
 		if (!ret)
 			goto retry;
 		return ret;
 	}

 	/*
 	 * Restore supervisor states: previous context switch etc has done
 	 * XSAVES and saved the supervisor states in the kernel buffer from
 	 * which they can be restored now.
 	 *
 	 * It would be optimal to handle this with a single XRSTORS, but
 	 * this does not work because the rest of the FPU registers have
 	 * been restored from a user buffer directly.
 	 */
 	if (test_thread_flag(TIF_NEED_FPU_LOAD) && xfeatures_mask_supervisor())
 		os_xrstor(&fpu->state.xsave, xfeatures_mask_supervisor());

 	fpregs_mark_activate();
 	fpregs_unlock();
 	return 0;
 }

 static int __fpu_restore_sig(void __user *buf, void __user *buf_fx,
 			     bool ia32_fxstate)
 {
 	int state_size = fpu_kernel_xstate_size;
 	struct task_struct *tsk = current;
 	struct fpu *fpu = &tsk->thread.fpu;
 	struct user_i387_ia32_struct env;
 	u64 user_xfeatures = 0;
 	bool fx_only = false;
 	int ret;

 	if (use_xsave()) {
 		struct _fpx_sw_bytes fx_sw_user;

 		ret = check_xstate_in_sigframe(buf_fx, &fx_sw_user);
 		if (unlikely(ret))
 			return ret;

 		fx_only = !fx_sw_user.magic1;
 		state_size = fx_sw_user.xstate_size;
 		user_xfeatures = fx_sw_user.xfeatures;
 	} else {
 		user_xfeatures = XFEATURE_MASK_FPSSE;
 	}

 	if (likely(!ia32_fxstate)) {
 		/*
 		 * Attempt to restore the FPU registers directly from user
 		 * memory. For that to succeed, the user access cannot cause page
 		 * faults. If it does, fall back to the slow path below, going
 		 * through the kernel buffer with the enabled pagefault handler.
 		 */
 		return restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only,
 						state_size);
 	}

 	/*
 	 * Copy the legacy state because the FP portion of the FX frame has
 	 * to be ignored for histerical raisins. The legacy state is folded
 	 * in once the larger state has been copied.
 	 */
 	ret = __copy_from_user(&env, buf, sizeof(env));
 	if (ret)
 		return ret;

 	/*
 	 * By setting TIF_NEED_FPU_LOAD it is ensured that our xstate is
 	 * not modified on context switch and that the xstate is considered
 	 * to be loaded again on return to userland (overriding last_cpu avoids
 	 * the optimisation).
 	 */
 	fpregs_lock();
 	if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
 		/*
 		 * If supervisor states are available then save the
 		 * hardware state in current's fpstate so that the
 		 * supervisor state is preserved. Save the full state for
 		 * simplicity. There is no point in optimizing this by only
 		 * saving the supervisor states and then shuffle them to
 		 * the right place in memory. It's ia32 mode. Shrug.
 		 */
 		if (xfeatures_mask_supervisor())
 			os_xsave(&fpu->state.xsave);
 		set_thread_flag(TIF_NEED_FPU_LOAD);
 	}
 	__fpu_invalidate_fpregs_state(fpu);
 	__cpu_invalidate_fpregs_state();
 	fpregs_unlock();

 	if (use_xsave() && !fx_only) {
 		ret = copy_sigframe_from_user_to_xstate(&fpu->state.xsave, buf_fx);
 		if (ret)
 			return ret;
 	} else {
 		if (__copy_from_user(&fpu->state.fxsave, buf_fx,
 				     sizeof(fpu->state.fxsave)))
 			return -EFAULT;

 		if (IS_ENABLED(CONFIG_X86_64)) {
 			/* Reject invalid MXCSR values. */
 			if (fpu->state.fxsave.mxcsr & ~mxcsr_feature_mask)
 				return -EINVAL;
 		} else {
 			/* Mask invalid bits out for historical reasons (broken hardware). */
 			fpu->state.fxsave.mxcsr &= ~mxcsr_feature_mask;
 		}

 		/* Enforce XFEATURE_MASK_FPSSE when XSAVE is enabled */
 		if (use_xsave())
 			fpu->state.xsave.header.xfeatures |= XFEATURE_MASK_FPSSE;
 	}

 	/* Fold the legacy FP storage */
 	convert_to_fxsr(&fpu->state.fxsave, &env);

 	fpregs_lock();
 	if (use_xsave()) {
 		/*
 		 * Remove all UABI feature bits not set in user_xfeatures
 		 * from the memory xstate header which makes the full
 		 * restore below bring them into init state. This works for
 		 * fx_only mode as well because that has only FP and SSE
 		 * set in user_xfeatures.
 		 *
 		 * Preserve supervisor states!
 		 */
 		u64 mask = user_xfeatures | xfeatures_mask_supervisor();

 		fpu->state.xsave.header.xfeatures &= mask;
 		ret = os_xrstor_safe(&fpu->state.xsave, xfeatures_mask_all);
 	} else {
 		ret = fxrstor_safe(&fpu->state.fxsave);
 	}

 	if (likely(!ret))
 		fpregs_mark_activate();

 	fpregs_unlock();
 	return ret;
 }
 static inline int xstate_sigframe_size(void)
 {
 	return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :
 			fpu_user_xstate_size;
 }

 /*
  * Restore FPU state from a sigframe:
  */
 int fpu__restore_sig(void __user *buf, int ia32_frame)
 {
 	unsigned int size = xstate_sigframe_size();
 	struct fpu *fpu = &current->thread.fpu;
 	void __user *buf_fx = buf;
 	bool ia32_fxstate = false;
 	int ret;

 	if (unlikely(!buf)) {
 		fpu__clear_user_states(fpu);
 		return 0;
 	}

 	ia32_frame &= (IS_ENABLED(CONFIG_X86_32) ||
 		       IS_ENABLED(CONFIG_IA32_EMULATION));

 	/*
 	 * Only FXSR enabled systems need the FX state quirk.
 	 * FRSTOR does not need it and can use the fast path.
 	 */
 	if (ia32_frame && use_fxsr()) {
 		buf_fx = buf + sizeof(struct fregs_state);
 		size += sizeof(struct fregs_state);
 		ia32_fxstate = true;
 	}

 	if (!access_ok(buf, size)) {
 		ret = -EACCES;
 		goto out;
 	}

 	if (!IS_ENABLED(CONFIG_X86_64) && !cpu_feature_enabled(X86_FEATURE_FPU)) {
 		ret = fpregs_soft_set(current, NULL, 0,
 				      sizeof(struct user_i387_ia32_struct),
 				      NULL, buf);
 	} else {
 		ret = __fpu_restore_sig(buf, buf_fx, ia32_fxstate);
 	}

 out:
 	if (unlikely(ret))
 		fpu__clear_user_states(fpu);
 	return ret;
 }

 unsigned long
 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 		     unsigned long *buf_fx, unsigned long *size)
 {
 	unsigned long frame_size = xstate_sigframe_size();

 	*buf_fx = sp = round_down(sp - frame_size, 64);
 	if (ia32_frame && use_fxsr()) {
 		frame_size += sizeof(struct fregs_state);
 		sp -= sizeof(struct fregs_state);
 	}

 	*size = frame_size;

 	return sp;
 }

 unsigned long fpu__get_fpstate_size(void)
 {
 	unsigned long ret = xstate_sigframe_size();

 	/*
 	 * This space is needed on (most) 32-bit kernels, or when a 32-bit
 	 * app is running on a 64-bit kernel. To keep things simple, just
 	 * assume the worst case and always include space for 'freg_state',
 	 * even for 64-bit apps on 64-bit kernels. This wastes a bit of
 	 * space, but keeps the code simple.
 	 */
 	if ((IS_ENABLED(CONFIG_IA32_EMULATION) ||
 	     IS_ENABLED(CONFIG_X86_32)) && use_fxsr())
 		ret += sizeof(struct fregs_state);

 	return ret;
 }

 /*
  * Prepare the SW reserved portion of the fxsave memory layout, indicating
  * the presence of the extended state information in the memory layout
  * pointed by the fpstate pointer in the sigcontext.
  * This will be saved when ever the FP and extended state context is
  * saved on the user stack during the signal handler delivery to the user.
  */
 void fpu__init_prepare_fx_sw_frame(void)
 {
 	int size = fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;

 	fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 	fx_sw_reserved.extended_size = size;
 	fx_sw_reserved.xfeatures = xfeatures_mask_uabi();
 	fx_sw_reserved.xstate_size = fpu_user_xstate_size;

 	if (IS_ENABLED(CONFIG_IA32_EMULATION) ||
 	    IS_ENABLED(CONFIG_X86_32)) {
 		int fsave_header_size = sizeof(struct fregs_state);

 		fx_sw_reserved_ia32 = fx_sw_reserved;
 		fx_sw_reserved_ia32.extended_size = size + fsave_header_size;
 	}
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* FPU signal frame handling routines.
	*/

	#include <linux/compat.h>
	#include <linux/cpu.h>
	#include <linux/pagemap.h>

	#include <asm/fpu/internal.h>
	#include <asm/fpu/signal.h>
	#include <asm/fpu/regset.h>
	#include <asm/fpu/xstate.h>

	#include <asm/sigframe.h>
	#include <asm/trace/fpu.h>

	static struct _fpx_sw_bytes fx_sw_reserved __ro_after_init;
	static struct _fpx_sw_bytes fx_sw_reserved_ia32 __ro_after_init;

	/*
	* Check for the presence of extended state information in the
	* user fpstate pointer in the sigcontext.
	*/
	static inline int check_xstate_in_sigframe(struct fxregs_state __user *fxbuf,
	struct _fpx_sw_bytes *fx_sw)
	{
	int min_xstate_size = sizeof(struct fxregs_state) +
	sizeof(struct xstate_header);
	void __user *fpstate = fxbuf;
	unsigned int magic2;

	if (__copy_from_user(fx_sw, &fxbuf->sw_reserved[0], sizeof(*fx_sw)))
	return -EFAULT;

	/* Check for the first magic field and other error scenarios. */
	if (fx_sw->magic1 != FP_XSTATE_MAGIC1 \|\|
	fx_sw->xstate_size < min_xstate_size \|\|
	fx_sw->xstate_size > fpu_user_xstate_size \|\|
	fx_sw->xstate_size > fx_sw->extended_size)
	goto setfx;

	/*
	* Check for the presence of second magic word at the end of memory
	* layout. This detects the case where the user just copied the legacy
	* fpstate layout with out copying the extended state information
	* in the memory layout.
	*/
	if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size)))
	return -EFAULT;

	if (likely(magic2 == FP_XSTATE_MAGIC2))
	return 0;
	setfx:
	trace_x86_fpu_xstate_check_failed(&current->thread.fpu);

	/* Set the parameters for fx only state */
	fx_sw->magic1 = 0;
	fx_sw->xstate_size = sizeof(struct fxregs_state);
	fx_sw->xfeatures = XFEATURE_MASK_FPSSE;
	return 0;
	}

	/*
	* Signal frame handlers.
	*/
	static inline int save_fsave_header(struct task_struct tsk, void __user buf)
	{
	if (use_fxsr()) {
	struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
	struct user_i387_ia32_struct env;
	struct _fpstate_32 __user *fp = buf;

	fpregs_lock();
	if (!test_thread_flag(TIF_NEED_FPU_LOAD))
	fxsave(&tsk->thread.fpu.state.fxsave);
	fpregs_unlock();

	convert_from_fxsr(&env, tsk);

	if (__copy_to_user(buf, &env, sizeof(env)) \|\|
	__put_user(xsave->i387.swd, &fp->status) \|\|
	__put_user(X86_FXSR_MAGIC, &fp->magic))
	return -1;
	} else {
	struct fregs_state __user *fp = buf;
	u32 swd;
	if (__get_user(swd, &fp->swd) \|\| __put_user(swd, &fp->status))
	return -1;
	}

	return 0;
	}

	static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
	{
	struct xregs_state __user *x = buf;
	struct _fpx_sw_bytes *sw_bytes;
	u32 xfeatures;
	int err;

	/* Setup the bytes not touched by the [f]xsave and reserved for SW. */
	sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
	err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));

	if (!use_xsave())
	return err;

	err \|= __put_user(FP_XSTATE_MAGIC2,
	(__u32 __user *)(buf + fpu_user_xstate_size));

	/*
	* Read the xfeatures which we copied (directly from the cpu or
	* from the state in task struct) to the user buffers.
	*/
	err \|= __get_user(xfeatures, (__u32 __user *)&x->header.xfeatures);

	/*
	* For legacy compatible, we always set FP/SSE bits in the bit
	* vector while saving the state to the user context. This will
	* enable us capturing any changes(during sigreturn) to
	* the FP/SSE bits by the legacy applications which don't touch
	* xfeatures in the xsave header.
	*
	* xsave aware apps can change the xfeatures in the xsave
	* header as well as change any contents in the memory layout.
	* xrestore as part of sigreturn will capture all the changes.
	*/
	xfeatures \|= XFEATURE_MASK_FPSSE;

	err \|= __put_user(xfeatures, (__u32 __user *)&x->header.xfeatures);

	return err;
	}

	static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
	{
	int err;

	if (use_xsave())
	err = xsave_to_user_sigframe(buf);
	else if (use_fxsr())
	err = fxsave_to_user_sigframe((struct fxregs_state __user *) buf);
	else
	err = fnsave_to_user_sigframe((struct fregs_state __user *) buf);

	if (unlikely(err) && __clear_user(buf, fpu_user_xstate_size))
	err = -EFAULT;
	return err;
	}

	/*
	* Save the fpu, extended register state to the user signal frame.
	*
	* 'buf_fx' is the 64-byte aligned pointer at which the [f\|fx\|x]save
	* state is copied.
	* 'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
	*
	* buf == buf_fx for 64-bit frames and 32-bit fsave frame.
	* buf != buf_fx for 32-bit frames with fxstate.
	*
	* Try to save it directly to the user frame with disabled page fault handler.
	* If this fails then do the slow path where the FPU state is first saved to
	* task's fpu->state and then copy it to the user frame pointed to by the
	* aligned pointer 'buf_fx'.
	*
	* If this is a 32-bit frame with fxstate, put a fsave header before
	* the aligned state at 'buf_fx'.
	*
	* For [f]xsave state, update the SW reserved fields in the [f]xsave frame
	* indicating the absence/presence of the extended state to the user.
	*/
	int copy_fpstate_to_sigframe(void __user buf, void __user buf_fx, int size)
	{
	struct task_struct *tsk = current;
	int ia32_fxstate = (buf != buf_fx);
	int ret;

	ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) \|\|
	IS_ENABLED(CONFIG_IA32_EMULATION));

	if (!static_cpu_has(X86_FEATURE_FPU)) {
	struct user_i387_ia32_struct fp;
	fpregs_soft_get(current, NULL, (struct membuf){.p = &fp,
	.left = sizeof(fp)});
	return copy_to_user(buf, &fp, sizeof(fp)) ? -EFAULT : 0;
	}

	if (!access_ok(buf, size))
	return -EACCES;
	retry:
	/*
	* Load the FPU registers if they are not valid for the current task.
	* With a valid FPU state we can attempt to save the state directly to
	* userland's stack frame which will likely succeed. If it does not,
	* resolve the fault in the user memory and try again.
	*/
	fpregs_lock();
	if (test_thread_flag(TIF_NEED_FPU_LOAD))
	fpregs_restore_userregs();

	pagefault_disable();
	ret = copy_fpregs_to_sigframe(buf_fx);
	pagefault_enable();
	fpregs_unlock();

	if (ret) {
	if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
	goto retry;
	return -EFAULT;
	}

	/* Save the fsave header for the 32-bit frames. */
	if ((ia32_fxstate \|\| !use_fxsr()) && save_fsave_header(tsk, buf))
	return -1;

	if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
	return -1;

	return 0;
	}

	static int __restore_fpregs_from_user(void __user *buf, u64 xrestore,
	bool fx_only)
	{
	if (use_xsave()) {
	u64 init_bv = xfeatures_mask_uabi() & ~xrestore;
	int ret;

	if (likely(!fx_only))
	ret = xrstor_from_user_sigframe(buf, xrestore);
	else
	ret = fxrstor_from_user_sigframe(buf);

	if (!ret && unlikely(init_bv))
	os_xrstor(&init_fpstate.xsave, init_bv);
	return ret;
	} else if (use_fxsr()) {
	return fxrstor_from_user_sigframe(buf);
	} else {
	return frstor_from_user_sigframe(buf);
	}
	}

	/*
	* Attempt to restore the FPU registers directly from user memory.
	* Pagefaults are handled and any errors returned are fatal.
	*/
	static int restore_fpregs_from_user(void __user *buf, u64 xrestore,
	bool fx_only, unsigned int size)
	{
	struct fpu *fpu = &current->thread.fpu;
	int ret;

	retry:
	fpregs_lock();
	pagefault_disable();
	ret = __restore_fpregs_from_user(buf, xrestore, fx_only);
	pagefault_enable();

	if (unlikely(ret)) {
	/*
	* The above did an FPU restore operation, restricted to
	* the user portion of the registers, and failed, but the
	* microcode might have modified the FPU registers
	* nevertheless.
	*
	* If the FPU registers do not belong to current, then
	* invalidate the FPU register state otherwise the task
	* might preempt current and return to user space with
	* corrupted FPU registers.
	*/
	if (test_thread_flag(TIF_NEED_FPU_LOAD))
	__cpu_invalidate_fpregs_state();
	fpregs_unlock();

	/* Try to handle #PF, but anything else is fatal. */
	if (ret != -EFAULT)
	return -EINVAL;

	ret = fault_in_pages_readable(buf, size);
	if (!ret)
	goto retry;
	return ret;
	}

	/*
	* Restore supervisor states: previous context switch etc has done
	* XSAVES and saved the supervisor states in the kernel buffer from
	* which they can be restored now.
	*
	* It would be optimal to handle this with a single XRSTORS, but
	* this does not work because the rest of the FPU registers have
	* been restored from a user buffer directly.
	*/
	if (test_thread_flag(TIF_NEED_FPU_LOAD) && xfeatures_mask_supervisor())
	os_xrstor(&fpu->state.xsave, xfeatures_mask_supervisor());

	fpregs_mark_activate();
	fpregs_unlock();
	return 0;
	}

	static int __fpu_restore_sig(void __user buf, void __user buf_fx,
	bool ia32_fxstate)
	{
	int state_size = fpu_kernel_xstate_size;
	struct task_struct *tsk = current;
	struct fpu *fpu = &tsk->thread.fpu;
	struct user_i387_ia32_struct env;
	u64 user_xfeatures = 0;
	bool fx_only = false;
	int ret;

	if (use_xsave()) {
	struct _fpx_sw_bytes fx_sw_user;

	ret = check_xstate_in_sigframe(buf_fx, &fx_sw_user);
	if (unlikely(ret))
	return ret;

	fx_only = !fx_sw_user.magic1;
	state_size = fx_sw_user.xstate_size;
	user_xfeatures = fx_sw_user.xfeatures;
	} else {
	user_xfeatures = XFEATURE_MASK_FPSSE;
	}

	if (likely(!ia32_fxstate)) {
	/*
	* Attempt to restore the FPU registers directly from user
	* memory. For that to succeed, the user access cannot cause page
	* faults. If it does, fall back to the slow path below, going
	* through the kernel buffer with the enabled pagefault handler.
	*/
	return restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only,
	state_size);
	}

	/*
	* Copy the legacy state because the FP portion of the FX frame has
	* to be ignored for histerical raisins. The legacy state is folded
	* in once the larger state has been copied.
	*/
	ret = __copy_from_user(&env, buf, sizeof(env));
	if (ret)
	return ret;

	/*
	* By setting TIF_NEED_FPU_LOAD it is ensured that our xstate is
	* not modified on context switch and that the xstate is considered
	* to be loaded again on return to userland (overriding last_cpu avoids
	* the optimisation).
	*/
	fpregs_lock();
	if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
	/*
	* If supervisor states are available then save the
	* hardware state in current's fpstate so that the
	* supervisor state is preserved. Save the full state for
	* simplicity. There is no point in optimizing this by only
	* saving the supervisor states and then shuffle them to
	* the right place in memory. It's ia32 mode. Shrug.
	*/
	if (xfeatures_mask_supervisor())
	os_xsave(&fpu->state.xsave);
	set_thread_flag(TIF_NEED_FPU_LOAD);
	}
	__fpu_invalidate_fpregs_state(fpu);
	__cpu_invalidate_fpregs_state();
	fpregs_unlock();

	if (use_xsave() && !fx_only) {
	ret = copy_sigframe_from_user_to_xstate(&fpu->state.xsave, buf_fx);
	if (ret)
	return ret;
	} else {
	if (__copy_from_user(&fpu->state.fxsave, buf_fx,
	sizeof(fpu->state.fxsave)))
	return -EFAULT;

	if (IS_ENABLED(CONFIG_X86_64)) {
	/* Reject invalid MXCSR values. */
	if (fpu->state.fxsave.mxcsr & ~mxcsr_feature_mask)
	return -EINVAL;
	} else {
	/* Mask invalid bits out for historical reasons (broken hardware). */
	fpu->state.fxsave.mxcsr &= ~mxcsr_feature_mask;
	}

	/* Enforce XFEATURE_MASK_FPSSE when XSAVE is enabled */
	if (use_xsave())
	fpu->state.xsave.header.xfeatures \|= XFEATURE_MASK_FPSSE;
	}

	/* Fold the legacy FP storage */
	convert_to_fxsr(&fpu->state.fxsave, &env);

	fpregs_lock();
	if (use_xsave()) {
	/*
	* Remove all UABI feature bits not set in user_xfeatures
	* from the memory xstate header which makes the full
	* restore below bring them into init state. This works for
	* fx_only mode as well because that has only FP and SSE
	* set in user_xfeatures.
	*
	* Preserve supervisor states!
	*/
	u64 mask = user_xfeatures \| xfeatures_mask_supervisor();

	fpu->state.xsave.header.xfeatures &= mask;
	ret = os_xrstor_safe(&fpu->state.xsave, xfeatures_mask_all);
	} else {
	ret = fxrstor_safe(&fpu->state.fxsave);
	}

	if (likely(!ret))
	fpregs_mark_activate();

	fpregs_unlock();
	return ret;
	}
	static inline int xstate_sigframe_size(void)
	{
	return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :
	fpu_user_xstate_size;
	}

	/*
	* Restore FPU state from a sigframe:
	*/
	int fpu__restore_sig(void __user *buf, int ia32_frame)
	{
	unsigned int size = xstate_sigframe_size();
	struct fpu *fpu = &current->thread.fpu;
	void __user *buf_fx = buf;
	bool ia32_fxstate = false;
	int ret;

	if (unlikely(!buf)) {
	fpu__clear_user_states(fpu);
	return 0;
	}

	ia32_frame &= (IS_ENABLED(CONFIG_X86_32) \|\|
	IS_ENABLED(CONFIG_IA32_EMULATION));

	/*
	* Only FXSR enabled systems need the FX state quirk.
	* FRSTOR does not need it and can use the fast path.
	*/
	if (ia32_frame && use_fxsr()) {
	buf_fx = buf + sizeof(struct fregs_state);
	size += sizeof(struct fregs_state);
	ia32_fxstate = true;
	}

	if (!access_ok(buf, size)) {
	ret = -EACCES;
	goto out;
	}

	if (!IS_ENABLED(CONFIG_X86_64) && !cpu_feature_enabled(X86_FEATURE_FPU)) {
	ret = fpregs_soft_set(current, NULL, 0,
	sizeof(struct user_i387_ia32_struct),
	NULL, buf);
	} else {
	ret = __fpu_restore_sig(buf, buf_fx, ia32_fxstate);
	}

	out:
	if (unlikely(ret))
	fpu__clear_user_states(fpu);
	return ret;
	}

	unsigned long
	fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
	unsigned long buf_fx, unsigned long size)
	{
	unsigned long frame_size = xstate_sigframe_size();

	*buf_fx = sp = round_down(sp - frame_size, 64);
	if (ia32_frame && use_fxsr()) {
	frame_size += sizeof(struct fregs_state);
	sp -= sizeof(struct fregs_state);
	}

	*size = frame_size;

	return sp;
	}

	unsigned long fpu__get_fpstate_size(void)
	{
	unsigned long ret = xstate_sigframe_size();

	/*
	* This space is needed on (most) 32-bit kernels, or when a 32-bit
	* app is running on a 64-bit kernel. To keep things simple, just
	* assume the worst case and always include space for 'freg_state',
	* even for 64-bit apps on 64-bit kernels. This wastes a bit of
	* space, but keeps the code simple.
	*/
	if ((IS_ENABLED(CONFIG_IA32_EMULATION) \|\|
	IS_ENABLED(CONFIG_X86_32)) && use_fxsr())
	ret += sizeof(struct fregs_state);

	return ret;
	}

	/*
	* Prepare the SW reserved portion of the fxsave memory layout, indicating
	* the presence of the extended state information in the memory layout
	* pointed by the fpstate pointer in the sigcontext.
	* This will be saved when ever the FP and extended state context is
	* saved on the user stack during the signal handler delivery to the user.
	*/
	void fpu__init_prepare_fx_sw_frame(void)
	{
	int size = fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;

	fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
	fx_sw_reserved.extended_size = size;
	fx_sw_reserved.xfeatures = xfeatures_mask_uabi();
	fx_sw_reserved.xstate_size = fpu_user_xstate_size;

	if (IS_ENABLED(CONFIG_IA32_EMULATION) \|\|
	IS_ENABLED(CONFIG_X86_32)) {
	int fsave_header_size = sizeof(struct fregs_state);

	fx_sw_reserved_ia32 = fx_sw_reserved;
	fx_sw_reserved_ia32.extended_size = size + fsave_header_size;
	}
	}