Commit b2681e79 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Borislav Petkov
Browse files

x86/fpu: Rename and sanitize fpu__save/copy() 



Both function names are a misnomer.

fpu__save() is actually about synchronizing the hardware register state
into the task's memory state so that either coredump or a math exception
handler can inspect the state at the time where the problem happens.

The function guarantees to preserve the register state, while "save" is a
common terminology for saving the current state so it can be modified and
restored later. This is clearly not the case here.

Rename it to fpu_sync_fpstate().

fpu__copy() is used to clone the current task's FPU state when duplicating
task_struct. While the register state is a copy the rest of the FPU state
is not.

Name it accordingly and remove the really pointless @src argument along
with the warning which comes along with it.

Nothing can ever copy the FPU state of a non-current task. It's clearly
just a consequence of arch_dup_task_struct(), but it makes no sense to
proliferate that further.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121455.196727450@linutronix.de
parent 784a4661

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

+4 −2
Original line number Diff line number Diff line
@@ -26,14 +26,16 @@ 
/*

 * High level FPU state handling functions:

 */

extern void fpu__save(struct fpu *fpu);

extern int  fpu__restore_sig(void __user *buf, int ia32_frame);

extern void fpu__drop(struct fpu *fpu);

extern int  fpu__copy(struct task_struct *dst, struct task_struct *src);

extern void fpu__clear_user_states(struct fpu *fpu);

extern void fpu__clear_all(struct fpu *fpu);

extern int  fpu__exception_code(struct fpu *fpu, int trap_nr);



extern void fpu_sync_fpstate(struct fpu *fpu);



extern int  fpu_clone(struct task_struct *dst);



/*

 * Boot time FPU initialization functions:

 */

arch/x86/kernel/fpu/core.c

+8 −9
Original line number Diff line number Diff line
@@ -159,11 +159,10 @@ void kernel_fpu_end(void) 
EXPORT_SYMBOL_GPL(kernel_fpu_end);



/*

 * Save the FPU state (mark it for reload if necessary):

 *

 * This only ever gets called for the current task.

 * Sync the FPU register state to current's memory register state when the

 * current task owns the FPU. The hardware register state is preserved.

 */

void fpu__save(struct fpu *fpu)

void fpu_sync_fpstate(struct fpu *fpu)

{

	WARN_ON_FPU(fpu != &current->thread.fpu);
@@ -221,18 +220,18 @@ void fpstate_init(union fpregs_state *state) 
}

EXPORT_SYMBOL_GPL(fpstate_init);



int fpu__copy(struct task_struct *dst, struct task_struct *src)

/* Clone current's FPU state on fork */

int fpu_clone(struct task_struct *dst)

{

	struct fpu *src_fpu = &current->thread.fpu;

	struct fpu *dst_fpu = &dst->thread.fpu;

	struct fpu *src_fpu = &src->thread.fpu;



	/* The new task's FPU state cannot be valid in the hardware. */

	dst_fpu->last_cpu = -1;



	if (!static_cpu_has(X86_FEATURE_FPU))

	if (!cpu_feature_enabled(X86_FEATURE_FPU))

		return 0;



	WARN_ON_FPU(src_fpu != &current->thread.fpu);



	/*

	 * Don't let 'init optimized' areas of the XSAVE area

	 * leak into the child task:

arch/x86/kernel/fpu/regset.c

+1 −1
Original line number Diff line number Diff line
@@ -41,7 +41,7 @@ int regset_xregset_fpregs_active(struct task_struct *target, const struct user_r 
static void sync_fpstate(struct fpu *fpu)

{

	if (fpu == &current->thread.fpu)

		fpu__save(fpu);

		fpu_sync_fpstate(fpu);

}



/*

arch/x86/kernel/process.c

+1 −2
Original line number Diff line number Diff line
@@ -87,8 +87,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) 
#ifdef CONFIG_VM86

	dst->thread.vm86 = NULL;

#endif



	return fpu__copy(dst, src);

	return fpu_clone(dst);

}



/*

arch/x86/kernel/traps.c

+3 −2
Original line number Diff line number Diff line
@@ -1046,9 +1046,10 @@ static void math_error(struct pt_regs *regs, int trapnr) 
	}



	/*

	 * Save the info for the exception handler and clear the error.

	 * Synchronize the FPU register state to the memory register state

	 * if necessary. This allows the exception handler to inspect it.

	 */

	fpu__save(fpu);

	fpu_sync_fpstate(fpu);



	task->thread.trap_nr	= trapnr;

	task->thread.error_code = 0;