linux-hardening - Re: [PATCH] pstore: ramoops: support pmsg size larger than kmalloc limitation

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Message-ID: <202306281053.EC5115465B@keescook>
Date:   Wed, 28 Jun 2023 10:55:58 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Yuxiao Zhang <yuxiaozhang@...gle.com>
Cc:     Tony Luck <tony.luck@...el.com>,
        "'Guilherme G . Piccoli'" <gpiccoli@...lia.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        wak@...gle.com
Subject: Re: [PATCH] pstore: ramoops: support pmsg size larger than kmalloc
 limitation

On Tue, Jun 27, 2023 at 01:25:41PM -0700, Yuxiao Zhang wrote:
> Current pmsg implementation is using kmalloc for pmsg record buffer,
> which has max size limits based on page size. Currently even we
> allocate enough space with pmsg-size, pmsg will still fail if the
> file size is larger than what kmalloc allowed.
> 
> Since we don't need physical contiguous memory for pmsg buffer
> , we can use kvmalloc to avoid such limitation.

Conceptually, I am fine with this change. I need a little time to trace
down the allocations. At first glance, I thought this patch only needed
to cover pstore_write_user_compat(), but I guess the read side needs to
be adjusted as well?

I'll double-check.

And yes, Greg's questions are all good -- fixing syntax and adding size
details in the commit log would be appreciated.

-Kees

-- 
Kees Cook