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

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Date:   Fri, 26 Oct 2018 19:16:28 +0100
From:   Kees Cook <keescook@...omium.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [RFC 6/6] Revert "pstore/ram_core: Do not reset restored zone's
 position and size"

On Fri, Oct 26, 2018 at 7:00 PM, Joel Fernandes (Google)
<joel@...lfernandes.org> 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
too.

-- 
Kees Cook