5.4-stable review patch. If anyone has any objections, please let me know.
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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