Re: [PATCH 14/14] pstore/platform: Remove automatic updates

[Kees Cook]

On Fri, May 18, 2012 at 3:26 PM, Anton Vorontsov
<anton.vorontsov@xxxxxxxxxx> wrote:
> Having automatic updates seems pointless, and even dangerous
> and thus counter-productive:
>
> 1. If we can mount pstore, or read files, we can as well read
>   /proc/kmsg. So, there's little point in duplicating the
>   functionality and present the same information but via another
>   userland ABI;
>
> 2. Expecting the kernel to behave sanely after oops/panic is naive.
>   It might work, but you'd rather not try it. Screwed up kernel
>   can do rather bad things, like recursive faults[1]; and pstore
>   rather provoking bad things to happen. It uses:
>
>   1. Timers (assumes sane interrupts state);
>   2. Workqueues and mutexes (assumes scheduler in a sane state);
>   3. kzalloc (a working slab allocator);
>
>   That's too much for a dead kernel, so the debugging facility
>   itself might just make debugging harder, which is not what
>   we want.
>
> So, let's remove the automatic updates, this keeps things simple
> and safe.
>
> (Maybe for non-oops message types it would make sense to add
> automatic updates, but so far I don't see any use case for this.
> Even for tracing, it has its own run-time/normal ABI, so we're
> only interested in pstore upon next boot, to retrieve what has
> gone wrong with HW or SW.)

Hrm. This complicates testing a bit. I need more convincing. :)

Systems run with panic_on_oops=0, and plenty of failure paths will
just kill "current" instead of bringing the entire system down. I
would much rather allow for the possibility to get oopses when they
happen than to have to wait a full reboot cycle to "notice" them.

-Kees

-- 
Kees Cook
Chrome OS Security
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