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

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Date:   Wed, 28 Jun 2023 07:30:16 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Yuxiao Zhang <yuxiaozhang@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>, Tony Luck <tony.luck@...el.com>,
        "'Guilherme G . Piccoli'" <gpiccoli@...lia.com>,
        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.

What is that max 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.

Odd placement of the ',' character :)

Anyway, thanks for getting this sent out.

But, what in-kernel user is hitting this in the pstore implementation?
How big of a buffer is it trying to create?  Is this a bug in older
kernels with the in-kernel drivers as well?  If so, should it go to
stable releases and how far back?

thanks,

greg k-h