Messages in this thread Patch in this message | | | From | Ben Hutchings <> | Date | Sat, 09 Sep 2017 22:47:40 +0100 | Subject | [PATCH 3.2 092/106] powerpc/64: Initialise thread_info for emergency stacks |
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3.2.93-rc1 review patch. If anyone has any objections, please let me know.
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From: Nicholas Piggin <npiggin@gmail.com>
commit 34f19ff1b5a0d11e46df479623d6936460105c9f upstream.
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.
Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com> Signed-off-by: Nicholas 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: Michael Ellerman <mpe@ellerman.id.au> [bwh: Backported to 3.2: - There's only one emergency stack - No need to call klp_init_thread_info() - Add the ti variable in emergency_stack_init()] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- arch/powerpc/kernel/setup_64.c | 31 ++++++++++++++++++++++++++++--- 1 file changed, 28 insertions(+), 3 deletions(-)
--- a/arch/powerpc/kernel/setup_64.c +++ b/arch/powerpc/kernel/setup_64.c @@ -509,6 +509,23 @@ static void __init exc_lvl_early_init(vo #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; +} + +/* * Stack space used when we detect a bad kernel stack pointer, and * early in SMP boots before relocation is enabled. */ @@ -525,12 +542,20 @@ static void __init emergency_stack_init( * 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) { unsigned long sp; + struct thread_info *ti; sp = memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit); + ti = __va(sp); + memset(ti, 0, THREAD_SIZE); + emerg_stack_init_thread_info(ti, i); sp += THREAD_SIZE; paca[i].emergency_sp = __va(sp); }
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