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

[Sibi Sankar <quic_sibis@quicinc.com>]

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.

- Sibi

> 
> Thanks,
> Robin.
> 
>>   drivers/remoteproc/qcom_q6v5_mss.c | 85 +++++++++++++++++++++---------
>>   1 file changed, 61 insertions(+), 24 deletions(-)
>>
>> diff --git a/drivers/remoteproc/qcom_q6v5_mss.c 
>> b/drivers/remoteproc/qcom_q6v5_mss.c
>> index fddb63cffee0..8264275ecbd0 100644
>> --- a/drivers/remoteproc/qcom_q6v5_mss.c
>> +++ b/drivers/remoteproc/qcom_q6v5_mss.c
>> @@ -211,6 +211,7 @@ struct q6v5 {
>>       size_t mba_size;
>>       size_t dp_size;
>> +    phys_addr_t mdata_phys;
>>       phys_addr_t mpss_phys;
>>       phys_addr_t mpss_reloc;
>>       size_t mpss_size;
>> @@ -935,6 +936,7 @@ static int q6v5_mpss_init_image(struct q6v5 
>> *qproc, const struct firmware *fw,
>>   {
>>       unsigned long dma_attrs = DMA_ATTR_FORCE_CONTIGUOUS | 
>> DMA_ATTR_NO_KERNEL_MAPPING;
>>       unsigned long flags = VM_DMA_COHERENT | VM_FLUSH_RESET_PERMS;
>> +    void *mdata_region;
>>       struct page **pages;
>>       struct page *page;
>>       dma_addr_t phys;
>> @@ -951,34 +953,48 @@ static int q6v5_mpss_init_image(struct q6v5 
>> *qproc, const struct firmware *fw,
>>       if (IS_ERR(metadata))
>>           return PTR_ERR(metadata);
>> -    page = dma_alloc_attrs(qproc->dev, size, &phys, GFP_KERNEL, 
>> dma_attrs);
>> -    if (!page) {
>> -        kfree(metadata);
>> -        dev_err(qproc->dev, "failed to allocate mdt buffer\n");
>> -        return -ENOMEM;
>> -    }
>> +    if (qproc->mdata_phys) {
>> +        mdata_region = memremap(qproc->mdata_phys, size, MEMREMAP_WC);
>> +        if (!mdata_region) {
>> +            dev_err(qproc->dev, "unable to map memory region: 
>> %pa+%zx\n",
>> +                &qproc->mdata_phys, size);
>> +            ret = -EBUSY;
>> +            goto free_dma_attrs;
>> +        }
>> -    count = PAGE_ALIGN(size) >> PAGE_SHIFT;
>> -    pages = kmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
>> -    if (!pages) {
>> -        ret = -ENOMEM;
>> -        goto free_dma_attrs;
>> -    }
>> +        memcpy(mdata_region, metadata, size);
>> +        memunmap(mdata_region);
>> +        phys = qproc->mdata_phys;
>> +    } else {
>> +        page = dma_alloc_attrs(qproc->dev, size, &phys, GFP_KERNEL, 
>> dma_attrs);
>> +        if (!page) {
>> +            kfree(metadata);
>> +            dev_err(qproc->dev, "failed to allocate mdt buffer\n");
>> +            return -ENOMEM;
>> +        }
>> -    for (i = 0; i < count; i++)
>> -        pages[i] = nth_page(page, i);
>> +        count = PAGE_ALIGN(size) >> PAGE_SHIFT;
>> +        pages = kmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
>> +        if (!pages) {
>> +            ret = -ENOMEM;
>> +            goto free_dma_attrs;
>> +        }
>> -    vaddr = vmap(pages, count, flags, pgprot_dmacoherent(PAGE_KERNEL));
>> -    kfree(pages);
>> -    if (!vaddr) {
>> -        dev_err(qproc->dev, "unable to map memory region: %pa+%zx\n", 
>> &phys, size);
>> -        ret = -EBUSY;
>> -        goto free_dma_attrs;
>> -    }
>> +        for (i = 0; i < count; i++)
>> +            pages[i] = nth_page(page, i);
>> -    memcpy(vaddr, metadata, size);
>> +        vaddr = vmap(pages, count, flags, 
>> pgprot_dmacoherent(PAGE_KERNEL));
>> +        kfree(pages);
>> +        if (!vaddr) {
>> +            dev_err(qproc->dev, "unable to map memory region: 
>> %pa+%zx\n", &phys, size);
>> +            ret = -EBUSY;
>> +            goto free_dma_attrs;
>> +        }
>> -    vunmap(vaddr);
>> +        memcpy(vaddr, metadata, size);
>> +
>> +        vunmap(vaddr);
>> +    }
>>       /* Hypervisor mapping to access metadata by modem */
>>       mdata_perm = BIT(QCOM_SCM_VMID_HLOS);
>> @@ -1008,7 +1024,8 @@ static int q6v5_mpss_init_image(struct q6v5 
>> *qproc, const struct firmware *fw,
>>                "mdt buffer not reclaimed system may become unstable\n");
>>   free_dma_attrs:
>> -    dma_free_attrs(qproc->dev, size, page, phys, dma_attrs);
>> +    if (!qproc->mdata_phys)
>> +        dma_free_attrs(qproc->dev, size, page, phys, dma_attrs);
>>       kfree(metadata);
>>       return ret < 0 ? ret : 0;
>> @@ -1882,6 +1899,26 @@ static int q6v5_alloc_memory_region(struct q6v5 
>> *qproc)
>>       qproc->mpss_phys = qproc->mpss_reloc = r.start;
>>       qproc->mpss_size = resource_size(&r);
>> +    if (!child) {
>> +        node = of_parse_phandle(qproc->dev->of_node, "memory-region", 
>> 2);
>> +    } else {
>> +        child = of_get_child_by_name(qproc->dev->of_node, "metadata");
>> +        node = of_parse_phandle(child, "memory-region", 0);
>> +        of_node_put(child);
>> +    }
>> +
>> +    if (!node)
>> +        return 0;
>> +
>> +    ret = of_address_to_resource(node, 0, &r);
>> +    of_node_put(node);
>> +    if (ret) {
>> +        dev_err(qproc->dev, "unable to resolve metadata region\n");
>> +        return ret;
>> +    }
>> +
>> +    qproc->mdata_phys = r.start;
>> +
>>       return 0;
>>   }