[PATCH 5.4 082/154] x86/fpu: Avoid copying dynamic FP state from init_task in arch_dup_task_struct()

Greg Kroah-Hartman
2025-04-08T12:05:51Z

From: Benjamin Berg <benjamin.berg@intel.com>

[ Upstream commit 5d3b81d4d8520efe888536b6906dc10fd1a228a8 ]

The init_task instance of struct task_struct is statically allocated and
may not contain the full FP state for userspace. As such, limit the copy
to the valid area of both init_task and 'dst' and ensure all memory is
initialized.

Note that the FP state is only needed for userspace, and as such it is
entirely reasonable for init_task to not contain parts of it.

Fixes: 5aaeb5c01c5b ("x86/fpu, sched: Introduce CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT and use it on x86")
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250226133136.816901-1-benjamin@sipsolutions.net
----

v2:
- Fix code if arch_task_struct_size < sizeof(init_task) by using
memcpy_and_pad.

Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kernel/process.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c402b079b74e8..cc9d682a98a13 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -96,7 +96,12 @@ EXPORT_PER_CPU_SYMBOL_GPL(__tss_limit_invalid);
*/
int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
{
- memcpy(dst, src, arch_task_struct_size);
+ /* 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);
+
#ifdef CONFIG_VM86
dst->thread.vm86 = NULL;
#endif
--
2.39.5