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

From: Kees Cook <keescook@chromium.org>
To: Yuxiao Zhang <yuxiaozhang@google.com>
Cc: Tony Luck <tony.luck@intel.com>,
	"'Guilherme G . Piccoli'" <gpiccoli@igalia.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
	wak@google.com
Subject: Re: [PATCH] pstore: ramoops: support pmsg size larger than kmalloc limitation
Date: Wed, 28 Jun 2023 10:55:58 -0700	[thread overview]
Message-ID: <202306281053.EC5115465B@keescook> (raw)
In-Reply-To: <20230627202540.881909-2-yuxiaozhang@google.com>

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