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

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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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-11-chang.seok.bae@intel.com
This commit is contained in:
Thomas Gleixner 2021-10-21 15:55:14 -07:00 • committed by Borislav Petkov
parent 53599b4d54
commit 9e798e9aa1
3 changed files with 27 additions and 12 deletions
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2
arch/x86/include/asm/fpu/sched.h
View file

@ -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);
/*

35
arch/x86/kernel/fpu/core.c
View file

@ -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 {
save_fpregs_to_fpstate(dst_fpu);
}
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);

2
arch/x86/kernel/process.c
View file

@ -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)) {