Re: [PATCH v3 2/5] efi: Add embedded peripheral firmware support

["Luis R. Rodriguez" <mcgrof@kernel.org>]

Android folks, poke below. otherwise we'll have no option but to seriously
consider Mimi's patch to prevent these calls when IMA appraisal is enforced:

http://lkml.kernel.org/r/1525182503-13849-7-git-send-email-zohar@linux.vnet.ibm.com

Please read below....

On Wed, Apr 25, 2018 at 05:55:57PM +0000, Luis R. Rodriguez wrote:
> On Wed, Apr 25, 2018 at 01:00:09AM -0400, Mimi Zohar wrote:
> > On Tue, 2018-04-24 at 23:42 +0000, Luis R. Rodriguez wrote:
> > > On Tue, Apr 24, 2018 at 12:07:01PM -0400, Mimi Zohar wrote:
> > > > On Tue, 2018-04-24 at 17:09 +0200, Hans de Goede wrote:
> > > If its of any help --
> > > 
> > > drivers/soc/qcom/mdt_loader.c is the only driver currently using
> > > request_firmware_into_buf() however I'll note qcom_mdt_load() is used in many
> > > other drivers so they are wrappers around request_firmware_into_buf():
> > > 
> > > drivers/gpu/drm/msm/adreno/a5xx_gpu.c:   * adreno_request_fw() handles this, but qcom_mdt_load() does
> > > drivers/gpu/drm/msm/adreno/a5xx_gpu.c:          ret = qcom_mdt_load(dev, fw, fwname, GPU_PAS_ID,
> > > drivers/gpu/drm/msm/adreno/a5xx_gpu.c:          ret = qcom_mdt_load(dev, fw, newname, GPU_PAS_ID,
> > > drivers/media/platform/qcom/venus/firmware.c:   ret = qcom_mdt_load(dev, mdt, fwname, VENUS_PAS_ID, mem_va, mem_phys,
> > > drivers/remoteproc/qcom_adsp_pil.c:     return qcom_mdt_load(adsp->dev, fw, rproc->firmware, adsp->pas_id,
> > > drivers/remoteproc/qcom_wcnss.c:        return qcom_mdt_load(wcnss->dev, fw, rproc->firmware, WCNSS_PAS_ID,
> > > 
> > > > > As such the current IMA code (from v4.17-rc2) actually does
> > > > > not handle READING_FIRMWARE_PREALLOC_BUFFER at all, 
> > > > 
> > > > Right, it doesn't yet address READING_FIRMWARE_PREALLOC_BUFFER, but
> > > > should.
> > > > 
> > > > Depending on whether the device requesting the firmware has access to
> > > > the DMA memory, before the signature verification, 
> > > 
> > > It would seem from the original patch review about READING_FIRMWARE_PREALLOC_BUFFER
> > > that this is not a DMA buffer.

To be very clear I believe Stephen implied this was not DMA buffer. Mimi
asked for READING_FIRMWARE_DMA if it was:

https://patchwork.kernel.org/patch/9074611/

> > The call sequence:
> > qcom_mdt_load() -> qcom_scm_pas_init_image() -> dma_alloc_coherent()
> > 
> > If dma_alloc_coherent() isn't allocating a DMA buffer, then the
> > function name is misleading/confusing.
> 
> Hah, by *definition* the device *and* processor has immediate access
> to data written *immediately* when dma_alloc_coherent() is used. From
> Documentation/DMA-API.txt:
> 
> -----------------------------------------------------------------------
> Part Ia - Using large DMA-coherent buffers                                      
> ------------------------------------------                                      
>                                                                                 
> ::                                                                              
>                                                                                 
>         void *                                                                  
>         dma_alloc_coherent(struct device *dev, size_t size,                     
>                            dma_addr_t *dma_handle, gfp_t flag)                  
>                                                                                 
> Consistent memory is memory for which a write by either the device or           
> the processor can immediately be read by the processor or device                
> without having to worry about caching effects.  (You may however need           
> to make sure to flush the processor's write buffers before telling              
> devices to read that memory.)  
> ------------------------------------------------------------------------
> 
> Is ptr below
> 
> 	ret = request_firmware_into_buf(&seg_fw, fw_name, dev,  
> 					ptr, phdr->p_filesz); 
> 
> Also part of the DMA buffer allocated earlier via:
> 
>         ret = qcom_scm_pas_init_image(pas_id, fw->data, fw->size);              
> 
> Android folks?

Android folks?

> > > The device driver should have access to the buffer pointer with write given
> > > that with request_firmware_into_buf() the driver is giving full write access to
> > > the memory pointer so that the firmware API can stuff the firmware it finds
> > > there.
> > > 
> > > Firmware signature verification would be up to the device hardware to do upon
> > > load *after* request_firmware_into_buf().
> > 
> > We're discussing the kernel's signature verification, not the device
> > hardware's signature verification.  Can the device driver access the
> > buffer, before IMA-appraisal has verified the firmware's signature?
> 
> It will depend on the above question.

  Luis