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SubjectRe: [PATCH] ARM: probes: Don't stop the machine if we're in the debugger
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On Mon, Aug 24, 2015 at 5:19 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
> On 08/24/2015 04:58 PM, Douglas Anderson wrote:
>>
>> If we're in kgdb then the machine is already stopped. Trying to stop
>> it again will cause us to try to sleep, which is not allowed while in
>> kgdb. To avoid this problem, only stop the machine when we're not in
>> kgdb.
>>
>> Reported-by: Aapo Vienamo <avienamo@nvidia.com>
>> Suggested-by: Kees Cook <keescook@chromium.org>

I actually suggested using in_atomic_preempt_off() which is I think a
better catch-all. Could you use that instead, please?

-Kees

>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
>> ---
>
>
> Can you add the backtrace?
>
>> arch/arm/kernel/patch.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
>> index 69bda1a..abf30ec 100644
>> --- a/arch/arm/kernel/patch.c
>> +++ b/arch/arm/kernel/patch.c
>> @@ -1,5 +1,6 @@
>> #include <linux/kernel.h>
>> #include <linux/spinlock.h>
>> +#include <linux/kgdb.h>
>> #include <linux/kprobes.h>
>> #include <linux/mm.h>
>> #include <linux/stop_machine.h>
>> @@ -124,6 +125,9 @@ void __kprobes patch_text(void *addr, unsigned int
>> insn)
>> .insn = insn,
>> };
>> - stop_machine(patch_text_stop_machine, &patch, NULL);
>> + /* Stop machine before patching; but not if in the debugger */
>> + if (unlikely(in_dbg_master()))
>> + patch_text_stop_machine(&patch);
>> + else
>> + stop_machine(patch_text_stop_machine, &patch, NULL);
>> }
>
>
> Perhaps it would be better to add a different function for the kgdb call
> site? Then it's explicit what's going on without us having to figure out
> when in_dbg_master() is true.
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project
>



--
Kees Cook
Chrome OS Security


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