From 08b0af5b2affbe7419853e8dd1330e4b3fe27125 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 29 Nov 2021 13:06:51 +0000 Subject: powerpc: Avoid discarding flags in system_call_exception() Some thread flags can be set remotely, and so even when IRQs are disabled, the flags can change under our feet. Thus, when setting flags we must use an atomic operation rather than a plain read-modify-write sequence, as a plain read-modify-write may discard flags which are concurrently set by a remote thread, e.g. // task A // task B tmp = A->thread_info.flags; set_tsk_thread_flag(A, NEWFLAG_B); tmp |= NEWFLAG_A; A->thread_info.flags = tmp; arch/powerpc/kernel/interrupt.c's system_call_exception() sets _TIF_RESTOREALL in the thread info flags with a read-modify-write, which may result in other flags being discarded. Elsewhere in the file it uses clear_bits() to atomically remove flag bits, so use set_bits() here for consistency with those. There may be reasons (e.g. instrumentation) that prevent the use of set_thread_flag() and clear_thread_flag() here, which would otherwise be preferable. Fixes: ae7aaecc3f2f78b7 ("powerpc/64s: system call rfscv workaround for TM bugs") Signed-off-by: Mark Rutland Signed-off-by: Thomas Gleixner Cc: Eirik Fuller Cc: Michael Ellerman Cc: Nicholas Piggin Link: https://lore.kernel.org/r/20211129130653.2037928-10-mark.rutland@arm.com --- arch/powerpc/kernel/interrupt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/powerpc') diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index 835b626cd476..df048e331cbf 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -148,7 +148,7 @@ notrace long system_call_exception(long r3, long r4, long r5, */ if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM) && unlikely(MSR_TM_TRANSACTIONAL(regs->msr))) - current_thread_info()->flags |= _TIF_RESTOREALL; + set_bits(_TIF_RESTOREALL, ¤t_thread_info()->flags); /* * If the system call was made with a transaction active, doom it and -- cgit v1.2.3-59-g8ed1b