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Message-ID: <fb8c5053-6dfc-f512-24a0-d00dd3f759a8@arm.com>
Date:   Wed, 14 Dec 2022 12:49:47 +0000
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Subject: Re: [PATCH 4/4] remoteproc: qcom_q6v5_mss: Use a carveout to
 authenticate modem headers
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To:     Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        Sibi Sankar <quic_sibis@quicinc.com>
Cc:     andersson@kernel.org, krzysztof.kozlowski+dt@linaro.org,
        robh+dt@kernel.org, agross@kernel.org,
        linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, konrad.dybcio@somainline.org,
        amit.pundir@linaro.org, regressions@leemhuis.info,
        sumit.semwal@linaro.org, will@kernel.org, catalin.marinas@arm.com
References: <20221213140724.8612-1-quic_sibis@quicinc.com>
 <20221213140724.8612-5-quic_sibis@quicinc.com>
 <741b64c2-0b09-6475-5736-d2cd3e33c34c@arm.com>
 <ba258979-0c65-4671-dd01-c1916c26e81b@quicinc.com>
 <20221213160722.GC4862@thinkpad>
From:   Robin Murphy <robin.murphy@arm.com>
In-Reply-To: <20221213160722.GC4862@thinkpad>
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On 2022-12-13 16:07, Manivannan Sadhasivam wrote:
> On Tue, Dec 13, 2022 at 09:27:04PM +0530, Sibi Sankar wrote:
>> Hey Robin,
>>
>> Thanks for taking time to review the series.
>>
>> On 12/13/22 20:37, Robin Murphy wrote:
>>> On 2022-12-13 14:07, Sibi Sankar wrote:
>>>> The memory region allocated using dma_alloc_attr with no kernel mapping
>>>> attribute set would still be a part of the linear kernel map. Any access
>>>> to this region by the application processor after assigning it to the
>>>> remote Q6 will result in a XPU violation. Fix this by replacing the
>>>> dynamically allocated memory region with a no-map carveout and unmap the
>>>> modem metadata memory region before passing control to the remote Q6.
>>>>
>>>> Reported-by: Amit Pundir <amit.pundir@linaro.org>
>>>> Fixes: 6c5a9dc2481b ("remoteproc: qcom: Make secure world call for
>>>> mem ownership switch")
>>>> Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
>>>> ---
>>>>
>>>> The addition of the carveout and memunmap is required only on SoCs that
>>>> mandate memory protection before transferring control to Q6, hence the
>>>> driver falls back to dynamic memory allocation in the absence of the
>>>> modem metadata carveout.
>>>
>>> The DMA_ATTR_NO_KERNEL_MAPPING stuff is still broken and pointless, so
>>> I'd expect to see this solution replacing it, not being added alongside.
>>> It's just silly to say pass the "I don't need a CPU mapping" flag, then
>>> manually open-code the same CPU mapping you would have got if you
>>> hadn't, in a way that only works at all when a cacheable alias exists
>>> anyway.
>>
>> only a subset of SoCs supported by the driver are affected by
>> the bug i.e. on the others dma_alloc_attr would still work
>> without problems. I can perhaps drop the NO_KERNEL_MAPPING along
>> with the vmap/vunmap and simplify things for those SoCs.
>>
> 
> Or perhaps revert fc156629b23a?

Oh, indeed, if it's already self-contained that's even neater. Basically 
that whole commit is based on a misunderstanding, doesn't actually do 
what it thinks it does, and you'd be far better off not maintaining the 
extra code.

Thanks,
Robin.