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x86/fpu: Always use memcpy_and_pad() in arch_dup_task_struct()

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It makes no sense to copy the bytes after sizeof(struct task_struct),
FPU state will be initialized in fpu_clone().

A plain memcpy(dst, src, sizeof(struct task_struct)) should work too,
but "_and_pad" looks safer.

[ mingo: Simplify it a bit more. ]

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S . Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250503143850.GA8997@redhat.com
This commit is contained in:
Oleg Nesterov 2025-05-03 16:38:50 +02:00 committed by Ingo Molnar
parent 8e269c030e
commit 2d299e3d77
1 changed files with 2 additions and 5 deletions
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7
arch/x86/kernel/process.c
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@ -93,11 +93,8 @@ EXPORT_PER_CPU_SYMBOL_GPL(__tss_limit_invalid);
*/
int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
{
/* init_task is not dynamically sized (incomplete FPU state) */
if (unlikely(src == &init_task))
memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(init_task), 0);
else
memcpy(dst, src, arch_task_struct_size);
/* fpu_clone() will initialize the "dst_fpu" memory */
memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(*dst), 0);
#ifdef CONFIG_VM86
dst->thread.vm86 = NULL;