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powerpc/64: Make stack tracing work during very early boot

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If we try to stack trace very early during boot, either due to a
WARN/BUG or manual dump_stack(), we will oops in
valid_emergency_stack() when we try to dereference the paca_ptrs
array.

The fix is simple, we just return false if paca_ptrs isn't allocated
yet. The stack pointer definitely isn't part of any emergency stack
because we haven't allocated any yet.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210202130207.1303975-1-mpe@ellerman.id.au
This commit is contained in:
Michael Ellerman 2021-02-03 00:02:06 +11:00
parent 73287caa92
commit 0ecf6a9e47
1 changed files with 3 additions and 0 deletions
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3
arch/powerpc/kernel/process.c
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@ -2047,6 +2047,9 @@ static inline int valid_emergency_stack(unsigned long sp, struct task_struct *p,
unsigned long stack_page;
unsigned long cpu = task_cpu(p);
if (!paca_ptrs)
return 0;
stack_page = (unsigned long)paca_ptrs[cpu]->emergency_sp - THREAD_SIZE;
if (sp >= stack_page && sp <= stack_page + THREAD_SIZE - nbytes)
return 1;