Commit 9e798e9a authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Borislav Petkov
Browse files

x86/fpu: Prepare fpu_clone() for dynamically enabled features 



The default portion of the parent's FPU state is saved in a child task.
With dynamic features enabled, the non-default portion is not saved in a
child's fpstate because these register states are defined to be
caller-saved. The new task's fpstate is therefore the default buffer.

Fork inherits the permission of the parent.

Also, do not use memcpy() when TIF_NEED_FPU_LOAD is set because it is
invalid when the parent has dynamic features.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-11-chang.seok.bae@intel.com
parent 53599b4d

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

+1 −1
Original line number Diff line number Diff line
@@ -11,7 +11,7 @@ 


extern void save_fpregs_to_fpstate(struct fpu *fpu);

extern void fpu__drop(struct fpu *fpu);

extern int  fpu_clone(struct task_struct *dst);

extern int  fpu_clone(struct task_struct *dst, unsigned long clone_flags);

extern void fpu_flush_thread(void);



/*

arch/x86/kernel/fpu/core.c

+25 −10
Original line number Diff line number Diff line
@@ -423,8 +423,20 @@ void fpstate_reset(struct fpu *fpu) 
	fpu->perm.__user_state_size	= fpu_user_cfg.default_size;

}



static inline void fpu_inherit_perms(struct fpu *dst_fpu)

{

	if (fpu_state_size_dynamic()) {

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



		spin_lock_irq(&current->sighand->siglock);

		/* Fork also inherits the permissions of the parent */

		dst_fpu->perm = src_fpu->perm;

		spin_unlock_irq(&current->sighand->siglock);

	}

}



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

int fpu_clone(struct task_struct *dst)

int fpu_clone(struct task_struct *dst, unsigned long clone_flags)

{

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

	struct fpu *dst_fpu = &dst->thread.fpu;
@@ -455,17 +467,20 @@ int fpu_clone(struct task_struct *dst) 
	}



	/*

	 * If the FPU registers are not owned by current just memcpy() the

	 * state.  Otherwise save the FPU registers directly into the

	 * child's FPU context, without any memory-to-memory copying.

	 * Save the default portion of the current FPU state into the

	 * clone. Assume all dynamic features to be defined as caller-

	 * saved, which enables skipping both the expansion of fpstate

	 * and the copying of any dynamic state.

	 *

	 * Do not use memcpy() when TIF_NEED_FPU_LOAD is set because

	 * copying is not valid when current uses non-default states.

	 */

	fpregs_lock();

	if (test_thread_flag(TIF_NEED_FPU_LOAD)) {

		memcpy(&dst_fpu->fpstate->regs, &src_fpu->fpstate->regs,

		       dst_fpu->fpstate->size);

	} else {

	if (test_thread_flag(TIF_NEED_FPU_LOAD))

		fpregs_restore_userregs();

	save_fpregs_to_fpstate(dst_fpu);

	}

	if (!(clone_flags & CLONE_THREAD))

		fpu_inherit_perms(dst_fpu);

	fpregs_unlock();



	trace_x86_fpu_copy_src(src_fpu);

arch/x86/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -157,7 +157,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg, 
	frame->flags = X86_EFLAGS_FIXED;

#endif



	fpu_clone(p);

	fpu_clone(p, clone_flags);



	/* Kernel thread ? */

	if (unlikely(p->flags & PF_KTHREAD)) {