linux-kernel - [tip: x86/fpu] x86/fpu: Always use memcpy_and_pad() in arch_dup_task

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Message-ID: <174634886368.22196.8705443193708873246.tip-bot2@tip-bot2>
Date: Sun, 04 May 2025 08:54:23 -0000
From: "tip-bot2 for Oleg Nesterov" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>,
 Andy Lutomirski <luto@...capital.net>, Brian Gerst <brgerst@...il.com>,
 "Chang S . Bae" <chang.seok.bae@...el.com>, "H. Peter Anvin" <hpa@...or.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: x86/fpu] x86/fpu: Always use memcpy_and_pad() in arch_dup_task_struct()

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     2d299e3d773d519ee93e5aaa3ffddd4a6276b005
Gitweb:        https://git.kernel.org/tip/2d299e3d773d519ee93e5aaa3ffddd4a6276b005
Author:        Oleg Nesterov <oleg@...hat.com>
AuthorDate:    Sat, 03 May 2025 16:38:50 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Sun, 04 May 2025 10:29:25 +02:00

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

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@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Chang S . Bae <chang.seok.bae@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: https://lore.kernel.org/r/20250503143850.GA8997@redhat.com
---
 arch/x86/kernel/process.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7a1bfb6..9e61807 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -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;