linux-kernel - Re: [PATCH 4/4] remoteproc: qcom_q6v5_mss: Use a carveout to authenticate modem headers

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Date:   Wed, 14 Dec 2022 12:49:47 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Sibi Sankar <quic_sibis@...cinc.com>
Cc:     andersson@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        robh+dt@...nel.org, agross@...nel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, konrad.dybcio@...ainline.org,
        amit.pundir@...aro.org, regressions@...mhuis.info,
        sumit.semwal@...aro.org, will@...nel.org, catalin.marinas@....com
Subject: Re: [PATCH 4/4] remoteproc: qcom_q6v5_mss: Use a carveout to
 authenticate modem headers

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@...aro.org>
>>>> Fixes: 6c5a9dc2481b ("remoteproc: qcom: Make secure world call for
>>>> mem ownership switch")
>>>> Signed-off-by: Sibi Sankar <quic_sibis@...cinc.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.