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Date:   Fri, 2 Sep 2022 14:28:38 +0200
From:   Johan Hovold <johan@kernel.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc:     Johan Hovold <johan+linaro@kernel.org>,
        Amol Maheshwari <amahesh@qti.qualcomm.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Bjorn Andersson <andersson@kernel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] misc: fastrpc: fix memory corruption
Message-ID: <YxH29vz2s62gGMnJ@hovoldconsulting.com>
References: <20220829080531.29681-1-johan+linaro@kernel.org>
 <01bdf6e2-f72a-e114-f3d2-deccf55403b1@linaro.org>
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On Fri, Sep 02, 2022 at 11:02:35AM +0100, Srinivas Kandagatla wrote:
> Hi Johan,
> 
> On 29/08/2022 09:05, Johan Hovold wrote:
> > The fastrpc driver uses a fixed-sized array to store its sessions but
> > missing and broken sanity checks could lead to memory beyond the array
> > being corrupted.
> > 
> > This specifically happens on SC8280XP platforms that use 14 sessions for
> > the compute DSP.
> > 
> Thanks for doing this.
> 
> I see that we hit this issue once again, and the way we are fixing it is 
> not really scalable. We should really get rid of FASTRPC_MAX_SESSIONS.

Yeah, I was a bit surprised to find that the underlying bugs (i.e. the
incomplete sanity checks) weren't fixed the last time this memory
corruption was reported:

	https://lore.kernel.org/all/1632123274-32054-1-git-send-email-jeyr@codeaurora.org/

> We should allocate the sessions dynamically based in the child node 
> count and qcom,nsessions.

That sounds like it would be an improvement.

But at least now you'll get an error message during probe rather than
silent memory corruption when bringing up a new SoC that needs more than
the current maximum number of sessions.

Johan