Commit dca99fb6 authored by Mark Rutland's avatar Mark Rutland Committed by Thomas Gleixner
Browse files

x86: Snapshot thread flags 



Some thread flags can be set remotely, and so even when IRQs are disabled,
the flags can change under our feet. Generally this is unlikely to cause a
problem in practice, but it is somewhat unsound, and KCSAN will
legitimately warn that there is a data race.

To avoid such issues, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20211129130653.2037928-12-mark.rutland@arm.com
parent 7ad63984

arch/x86/kernel/process.c

+4 −4
Original line number Diff line number Diff line
@@ -365,7 +365,7 @@ void arch_setup_new_exec(void) 
		clear_thread_flag(TIF_SSBD);

		task_clear_spec_ssb_disable(current);

		task_clear_spec_ssb_noexec(current);

		speculation_ctrl_update(task_thread_info(current)->flags);

		speculation_ctrl_update(read_thread_flags());

	}

}
@@ -617,7 +617,7 @@ static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk) 
			clear_tsk_thread_flag(tsk, TIF_SPEC_IB);

	}

	/* Return the updated threadinfo flags*/

	return task_thread_info(tsk)->flags;

	return read_task_thread_flags(tsk);

}



void speculation_ctrl_update(unsigned long tif)
@@ -653,8 +653,8 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p) 
{

	unsigned long tifp, tifn;



	tifn = READ_ONCE(task_thread_info(next_p)->flags);

	tifp = READ_ONCE(task_thread_info(prev_p)->flags);

	tifn = read_task_thread_flags(next_p);

	tifp = read_task_thread_flags(prev_p);



	switch_to_bitmap(tifp);

arch/x86/kernel/process.h

+2 −2
Original line number Diff line number Diff line
@@ -13,8 +13,8 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p); 
static inline void switch_to_extra(struct task_struct *prev,

				   struct task_struct *next)

{

	unsigned long next_tif = task_thread_info(next)->flags;

	unsigned long prev_tif = task_thread_info(prev)->flags;

	unsigned long next_tif = read_task_thread_flags(next);

	unsigned long prev_tif = read_task_thread_flags(prev);



	if (IS_ENABLED(CONFIG_SMP)) {

		/*

arch/x86/mm/tlb.c

+1 −1
Original line number Diff line number Diff line
@@ -361,7 +361,7 @@ static void l1d_flush_evaluate(unsigned long prev_mm, unsigned long next_mm, 


static unsigned long mm_mangle_tif_spec_bits(struct task_struct *next)

{

	unsigned long next_tif = task_thread_info(next)->flags;

	unsigned long next_tif = read_task_thread_flags(next);

	unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK;



	/*