Re: [PATCH] spi: Assign dummy scatterlist to unidirectional transfers

[Yongqin Liu]

On Thu, 30 May 2024 at 05:04, Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote:
>
> Wed, May 29, 2024 at 11:42:35AM -0400, Nícolas F. R. A. Prado kirjoitti:
> > From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> >
> > Commit 8cc3bad9d9d6 ("spi: Remove unneded check for orig_nents")
> > introduced a regression: unmapped data could now be passed to the DMA
> > APIs, resulting in null pointer dereferences. Commit 9f788ba457b4 ("spi:
> > Don't mark message DMA mapped when no transfer in it is") and commit
> > da560097c056 ("spi: Check if transfer is mapped before calling DMA sync
> > APIs") addressed the problem, but only partially. Unidirectional
> > transactions will still result in null pointer dereference. To prevent
> > that from happening, assign a dummy scatterlist when no data is mapped,
> > so that the DMA API can be called and not result in a null pointer
> > dereference.
>
> I feel that with this the da560097c056 ("spi: Check if transfer is mapped
> before calling DMA sync APIs") can be reverted as unneeded. Nícolas, can
> you check that? If it works, we better revert the unneeded checks.

FYI, just tested based on the Android Common Kernel android-mainline branch,
with only the following two changes, the issue is not reported too:
    9dedabe95b49 spi: Assign dummy scatterlist to unidirectional transfers
    9f788ba457b4 spi: Don't mark message DMA mapped when no transfer in it is


-- 
Best Regards,
Yongqin Liu
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