From cb7ca40a3882360ce87191793449d48df0b29184 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Wed, 9 Apr 2025 23:11:22 +0200 Subject: x86/fpu: Make task_struct::thread constant size Turn thread.fpu into a pointer. Since most FPU code internals work by passing around the FPU pointer already, the code generation impact is small. This allows us to remove the old kludge of task_struct being variable size: struct task_struct { ... /* * New fields for task_struct should be added above here, so that * they are included in the randomized portion of task_struct. */ randomized_struct_fields_end /* CPU-specific state of this task: */ struct thread_struct thread; /* * WARNING: on x86, 'thread_struct' contains a variable-sized * structure. It *MUST* be at the end of 'task_struct'. * * Do not put anything below here! */ }; ... which creates a number of problems, such as requiring thread_struct to be the last member of the struct - not allowing it to be struct-randomized, etc. But the primary motivation is to allow the decoupling of task_struct from hardware details ( in particular), and to eventually allow the per-task infrastructure: DECLARE_PER_TASK(type, name); ... per_task(current, name) = val; ... which requires task_struct to be a constant size struct. The fpu_thread_struct_whitelist() quirk to hardened usercopy can be removed, now that the FPU structure is not embedded in the task struct anymore, which reduces text footprint a bit. Fixed-by: Oleg Nesterov Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Brian Gerst Cc: Chang S. Bae Cc: H. Peter Anvin Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250409211127.3544993-4-mingo@kernel.org --- include/linux/sched.h | 15 ++++----------- 1 file changed, 4 insertions(+), 11 deletions(-) (limited to 'include/linux') diff --git a/include/linux/sched.h b/include/linux/sched.h index f96ac1982893..4ecc0c6b1cb0 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1646,22 +1646,15 @@ struct task_struct { struct user_event_mm *user_event_mm; #endif - /* - * New fields for task_struct should be added above here, so that - * they are included in the randomized portion of task_struct. - */ - randomized_struct_fields_end - /* CPU-specific state of this task: */ struct thread_struct thread; /* - * WARNING: on x86, 'thread_struct' contains a variable-sized - * structure. It *MUST* be at the end of 'task_struct'. - * - * Do not put anything below here! + * New fields for task_struct should be added above here, so that + * they are included in the randomized portion of task_struct. */ -}; + randomized_struct_fields_end +} __attribute__ ((aligned (64))); #define TASK_REPORT_IDLE (TASK_REPORT + 1) #define TASK_REPORT_MAX (TASK_REPORT_IDLE << 1) -- cgit v1.2.3