Re: [RFC 6/6] Revert "pstore/ram_core: Do not reset restored zone's position and size"

From: Kees Cook
Date: Fri Oct 26 2018 - 14:16:36 EST

On Fri, Oct 26, 2018 at 7:00 PM, Joel Fernandes (Google)
<joel@xxxxxxxxxxxxxxxxx> wrote:
> This reverts commit 25b63da64708212985c06c7f8b089d356efdd9cf.
> Due to the commit which is being reverted here, it is not possible to
> know if pstore's messages were from a previous boot, or from very old
> boots. This creates an awkard situation where its unclear if crash or
> other logs are from the previous boot or from very old boots. Also
> typically we dump the pstore buffers after one reboot and are interested
> in only the previous boot's crash so let us reset the buffer after we
> save them.
> Lastly, if we don't zap them, then I think it is possible that part of
> the buffer will be from this boot and the other parts will be from
> previous boots. So this revert fixes all of this by calling
> persistent_ram_zap always.

I like the other patches (comments coming), but not this one: it's
very intentional to keep all crashes around until they're explicitly
unlinked from the pstore filesystem from userspace. Especially true
for catching chains of kernel crashes, or a failed log collection,
etc. Surviving multiple reboots is the expected behavior on Chrome OS

Kees Cook