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Subject[PATCH 4.9 168/172] arm64: fix NULL dereference in have_cpu_die()
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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Salter <msalter@redhat.com>

commit 335d2c2d192266358c5dfa64953a4c162f46e464 upstream.

Commit 5c492c3f5255 ("arm64: smp: Add function to determine if cpus are
stuck in the kernel") added a helper function to determine if die() is
supported in cpu_ops. This function assumes a cpu will have a valid
cpu_ops entry, but that may not be the case for cpu0 is spin-table or
parking protocol is used to boot secondary cpus. In that case, there
is a NULL dereference if have_cpu_die() is called by cpu0. So add a
check for a valid cpu_ops before dereferencing it.

Fixes: 5c492c3f5255 ("arm64: smp: Add function to determine if cpus are stuck in the kernel")
Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/kernel/smp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -934,7 +934,7 @@ static bool have_cpu_die(void)
#ifdef CONFIG_HOTPLUG_CPU
int any_cpu = raw_smp_processor_id();

- if (cpu_ops[any_cpu]->cpu_die)
+ if (cpu_ops[any_cpu] && cpu_ops[any_cpu]->cpu_die)
return true;
#endif
return false;

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