Re: [PATCH] pstore: use ktime_get_real_fast_ns() instead of __getnstimeofday()

[Kees Cook]

On Thu, Nov 9, 2017 at 4:46 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> On Fri, 10 Nov 2017, Arnd Bergmann wrote:
>> On Fri, Nov 10, 2017 at 12:00 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>> > Hmm, no. None of the regular accessor functions can be called from NMI
>> > context safely.
>>
>> Right, that's what I mean: it must not get called from NMI context, but it
>> currently is, at least for this case:
>>
>> NMI handler:
>>   something bad
>>     panic()
>>       kmsg_dump()
>>         pstore_dump()
>>            pstore_record_init()
>>              __getnstimeofday()
>>
>> I should probably add that to the changelog text ;-)
>
> Indeed.

Er, so, is this safe to call there? I've had to fix this a few times
now, so if using ktime_get_real_fast_ns() can be used here (and
doesn't return 0) then this is easily an improvement over the existing
"maybe read 0" case pstore has now.

-Kees


-- 
Kees Cook
Pixel Security