On Sun, Jul 12, 2020 at 11:28:37AM +0100, Jon Hunter wrote:
> After commit cad064f1bd52 ("devres: handle zero size in devm_kmalloc()")
> was added system suspend started failing on Tegra186. The kernel log
> showed that the Tegra XHCI driver was crashing on entry to suspend when
> attemptin the save the USB context. The problem is caused because we
> are trying to allocate a zero length array for the IPFS context on
> Tegra186 and following commit cad064f1bd52 ("devres: handle zero size
> in devm_kmalloc()") this now causes a NULL pointer deference crash
> when we try to access the memory. Fix this by only allocating memory
> for both the IPFS and FPCI contexts when required.
>
> Cc: [email protected]
>
> Fixes: 5c4e8d3781bc ("usb: host: xhci-tegra: Add support for XUSB context
> save/restore")
>
> Signed-off-by: Jon Hunter <[email protected]>
> ---
> drivers/usb/host/xhci-tegra.c | 22 ++++++++++++++--------
> 1 file changed, 14 insertions(+), 8 deletions(-)Actually it would seem to me that this is no longer a bug after your fix in patch 1. We only ever access tegra->context.ipfs if tegra->soc->ipfs.num_offsets > 0, so the special ZERO_SIZE_PTR case will not actually cause an issue anymore. The reason why this was crashing was because tegra->context.fpci was allocated with a zero size (because of the bug that you fixed in patch 1) and then that zero-size pointer was dereferenced because the code was correctly checking for tegra->soc->fpci.num_offsets > 0 in the context save and restore. So I don't think there's a bug here. It's not wrong to allocate a zero- size buffer. It's only a bug to then go and dereference it. Are you still seeing the issue if you leave out this patch and only apply patch 1? Thierry
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