Re: Crash in msm serial on dragonboard with ftrace bootargs

[Kees Cook <keescook@chromium.org>]

On Wed, Oct 17, 2018 at 10:56 AM, Joel Fernandes <joel@joelfernandes.org> wrote:
> On Wed, Oct 17, 2018 at 08:19:41PM +0530, Sai Prakash Ranjan wrote:
>> On 10/17/2018 5:08 PM, Sai Prakash Ranjan wrote:
>> > >
>> > > What do you think about the (untested) patch below? It seems to me
>> > > that it
>> > > should solve the issue of missing early crash dumps, but I have not
>> > > tested it
>> > > yet. Sai, would you mind trying it out and let me know if you can see the
>> > > early crash dumps properly now?
>> > >
>> > > ----8<---
>> > > From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
>> > > Subject: [RFC] pstore: allocate compression during late_initcall
>> > >
>> > > ramoop's pstore registration (using pstore_register) has to run during
>> > > late_initcall because crypto backend may not be ready during
>> > > postcore_initcall. This causes missing of dmesg crash dumps which could
>> > > have been caught by pstore.
>> > >
>> > > Instead, lets allow ramoops pstore registration earlier, and once crypto
>> > > is ready we can initialize the compression.
>> > >
>> > > Reported-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
>> > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>> > > ---
>> > >   fs/pstore/platform.c | 13 +++++++++++++
>> > >   fs/pstore/ram.c      |  2 +-
>> > >   2 files changed, 14 insertions(+), 1 deletion(-)
>> > >
>> > > diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
>> > > index 15e99d5a681d..f09066db2d4d 100644
>> > > --- a/fs/pstore/platform.c
>> > > +++ b/fs/pstore/platform.c
>> > > @@ -780,6 +780,19 @@ void __init pstore_choose_compression(void)
>> > >       }
>> > >   }
>> > > +static int __init pstore_compression_late_init(void)
>> > > +{
>> > > +    /*
>> > > +     * Check if any pstore backends registered earlier but did not
>> > > allocate
>> > > +     * for compression because crypto was not ready, if so then
>> > > initialize
>> > > +     * compression.
>> > > +     */
>> > > +    if (psinfo && !tfm)
>> > > +        allocate_buf_for_compression();
>> > > +    return 0;
>> > > +}
>> > > +late_initcall(pstore_compression_late_init);
>> > > +
>> > >   module_param(compress, charp, 0444);
>> > >   MODULE_PARM_DESC(compress, "Pstore compression to use");
>> > > diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
>> > > index bbd1e357c23d..98e48d1a9776 100644
>> > > --- a/fs/pstore/ram.c
>> > > +++ b/fs/pstore/ram.c
>> > > @@ -940,7 +940,7 @@ static int __init ramoops_init(void)
>> > >       ramoops_register_dummy();
>> > >       return platform_driver_register(&ramoops_driver);
>> > >   }
>> > > -late_initcall(ramoops_init);
>> > > +postcore_initcall(ramoops_init);
>> > >   static void __exit ramoops_exit(void)
>> > >   {
>> > >
>> >
>> > Yes I could see the early crash dump. Also I tested with different
>> > compression (LZO) instead of deflate just to be sure and it works fine,
>> > thanks :)
>> >
>> > Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
>> >
>
> Thanks.
>
>> I just noticed that allocate_buf_for_compression() is also called from
>> pstore_register(). Shouldn't that call be removed now that ramoops_init is
>> moved to postcore_initcall and allocate_buf_for_compression() will just
>> return doing nothing when called from pstore_register()?
>
> Yes, that is the point. If crypto is not ready then my thought is
> allocate_buf_for_compression() called from pstore_register() should do
> nothing and pstore will work uncompressed and the kdump infrastructure will
> only cause uncompressed writes. But say if the kdump triggered *after* crypto
> was ready, then the dump write out would be compressed since pstore is ready
> for compression.
>
> The idea is if a future pstore backend calls pstore_register late, then it
> may as well do the allocate_buf_for_compression as well at that time when it
> runs. In that cause pstore_compression_late_init would do nothing.
>
> So this approach is both dynamic and future proof.

Yeah, thanks! I think this looks correct, but I'll spend some more
time testing it too.

-Kees

-- 
Kees Cook
Pixel Security