On Mon, Dec 09, 2024 at 03:27:56PM +0100, Krzysztof Kozlowski wrote:
> The SCM driver can defer or fail probe, or just load a bit later so
> callers of qcom_scm_assign_mem() should defer if the device is not ready.
>
> This fixes theoretical NULL pointer exception, triggered via introducing
> probe deferral in SCM driver with call trace:
>
> qcom_tzmem_alloc+0x70/0x1ac (P)
> qcom_tzmem_alloc+0x64/0x1ac (L)
> qcom_scm_assign_mem+0x78/0x194
> qcom_rmtfs_mem_probe+0x2d4/0x38c
> platform_probe+0x68/0xc8
>
> Fixes: d82bd359972a ("firmware: scm: Add new SCM call API for switching memory ownership")
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
>
> ---
>
> I am not sure about commit introducing it (Fixes tag) thus not Cc-ing
> stable.
> ---
> drivers/firmware/qcom/qcom_scm.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index 5d91b8e22844608f35432f1ba9c08d477d4ff762..93212c8f20ad65ecc44804b00f4b93e3eaaf8d95 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -1075,6 +1075,9 @@ int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
> int ret, i, b;
> u64 srcvm_bits = *srcvm;
>
> + if (!qcom_scm_is_available())
> + return -EPROBE_DEFER;
This API is generally called from places other than probe, making the
return of EPROBE_DEFER undesirable. While not pretty, a client depending
on the scm driver to be probed is expected to call
qcom_scm_is_available().
qcom_rmtfs_mem_probe() does this right before calling
qcom_scm_assign_mem(), am I misunderstanding the case you're describing?
Regards,
Bjorn
> +
> src_sz = hweight64(srcvm_bits) * sizeof(*src);
> mem_to_map_sz = sizeof(*mem_to_map);
> dest_sz = dest_cnt * sizeof(*destvm);
>
> --
> 2.43.0
>
