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

[Robin Murphy]

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