The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 34f19ff1b5a0d11e46df479623d6936460105c9f Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@xxxxxxxxx>
Date: Wed, 21 Jun 2017 15:58:29 +1000
Subject: [PATCH] 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@xxxxxxxxxxxxxxx
Reported-by: Abdul Haleem <abdhalee@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
[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@xxxxxxxxxxxxxx>
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index a8c1f99e9607..4640f6d64f8b 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -616,6 +616,24 @@ 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
* stack for machine checks.
@@ -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
}