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Commit 34f19ff1 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/64: Initialise thread_info for emergency stacks 



Emergency stacks have their thread_info mostly uninitialised, which in
particular means garbage preempt_count values.

Emergency stack code runs with interrupts disabled entirely, and is
used very rarely, so this has been unnoticed so far. It was found by a
proposed new powerpc watchdog that takes a soft-NMI directly from the
masked_interrupt handler and using the emergency stack. That crashed
at BUG_ON(in_nmi()) in nmi_enter(). preempt_count()s were found to be
garbage.

To fix this, zero the entire THREAD_SIZE allocation, and initialize
the thread_info.

Cc: stable@vger.kernel.org
Reported-by: default avatarAbdul Haleem <abdhalee@linux.vnet.ibm.com>
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
[mpe: Move it all into setup_64.c, use a function not a macro. Fix
      crashes on Cell by setting preempt_count to 0 not HARDIRQ_OFFSET]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent bbd5ff50

arch/powerpc/kernel/setup_64.c

+28 −3
Original line number Diff line number Diff line
@@ -615,6 +615,24 @@ void __init exc_lvl_early_init(void) 
}

#endif



/*

 * Emergency stacks are used for a range of things, from asynchronous

 * NMIs (system reset, machine check) to synchronous, process context.

 * We set preempt_count to zero, even though that isn't necessarily correct. To

 * get the right value we'd need to copy it from the previous thread_info, but

 * doing that might fault causing more problems.

 * TODO: what to do with accounting?

 */

static void emerg_stack_init_thread_info(struct thread_info *ti, int cpu)

{

	ti->task = NULL;

	ti->cpu = cpu;

	ti->preempt_count = 0;

	ti->local_flags = 0;

	ti->flags = 0;

	klp_init_thread_info(ti);

}



/*

 * Stack space used when we detect a bad kernel stack pointer, and

 * early in SMP boots before relocation is enabled. Exclusive emergency
@@ -633,24 +651,31 @@ void __init emergency_stack_init(void) 
	 * Since we use these as temporary stacks during secondary CPU

	 * bringup, we need to get at them in real mode. This means they

	 * must also be within the RMO region.

	 *

	 * The IRQ stacks allocated elsewhere in this file are zeroed and

	 * initialized in kernel/irq.c. These are initialized here in order

	 * to have emergency stacks available as early as possible.

	 */

	limit = min(safe_stack_limit(), ppc64_rma_size);



	for_each_possible_cpu(i) {

		struct thread_info *ti;

		ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));

		klp_init_thread_info(ti);

		memset(ti, 0, THREAD_SIZE);

		emerg_stack_init_thread_info(ti, i);

		paca[i].emergency_sp = (void *)ti + THREAD_SIZE;



#ifdef CONFIG_PPC_BOOK3S_64

		/* emergency stack for NMI exception handling. */

		ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));

		klp_init_thread_info(ti);

		memset(ti, 0, THREAD_SIZE);

		emerg_stack_init_thread_info(ti, i);

		paca[i].nmi_emergency_sp = (void *)ti + THREAD_SIZE;



		/* emergency stack for machine check exception handling. */

		ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));

		klp_init_thread_info(ti);

		memset(ti, 0, THREAD_SIZE);

		emerg_stack_init_thread_info(ti, i);

		paca[i].mc_emergency_sp = (void *)ti + THREAD_SIZE;

#endif

	}