On Mon, May 04, 2026 at 10:47:00PM +0530, Mukesh Ojha wrote:
> A NULL pointer dereference was observed on Hawi at boot when the DSP
> sends a glink message before fastrpc_rpmsg_probe() has completed
> initialization:
>
> Unable to handle kernel NULL pointer dereference at virtual address
> 0000000000000178
> pc : _raw_spin_lock_irqsave+0x34/0x8c
> lr : fastrpc_rpmsg_callback+0x3c/0xcc [fastrpc]
> ...
> Call trace:
> _raw_spin_lock_irqsave+0x34/0x8c (P)
> fastrpc_rpmsg_callback+0x3c/0xcc [fastrpc]
> qcom_glink_native_rx+0x538/0x6a4
> qcom_glink_smem_intr+0x14/0x24 [qcom_glink_smem]
>
> The faulting address 0x178 corresponds to the lock variable inside
> struct fastrpc_channel_ctx, confirming that cctx is NULL when
> fastrpc_rpmsg_callback() attempts to take the spinlock.
>
> There are two issues here. First, dev_set_drvdata() is called before
> spin_lock_init() and idr_init(), leaving a window where the callback
> can retrieve a valid cctx pointer but operate on an uninitialized
> spinlock. Second, the rpmsg channel becomes live as soon as the driver
> is bound, so fastrpc_rpmsg_callback() can fire before dev_set_drvdata()
> is called at all, resulting in dev_get_drvdata() returning NULL.
>
> Fix both issues by moving all cctx initialization ahead of
> dev_set_drvdata() so the structure is fully initialized before it
> becomes visible to the callback, and add a NULL check in
> fastrpc_rpmsg_callback() as a guard against any remaining window.
>
> Fixes: f6f9279f2bf0 ("misc: fastrpc: Add Qualcomm fastrpc basic driver model")
> Cc: [email protected]
> Signed-off-by: Mukesh Ojha <[email protected]>
The fix looks good to me.
Reviewed-by: Bjorn Andersson <[email protected]>
But I can't help wonder, what's in that message? Should we make sure to
handle it, longer term?
Regards,
Bjorn
> ---
> Changes in v2:
> https://lore.kernel.org/lkml/[email protected]/
> - Added stable mailing list and fixes tag.
>
> drivers/misc/fastrpc.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 1080f9acf70a..a1a54453bb7e 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -2431,7 +2431,6 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device
> *rpdev)
>
> kref_init(&data->refcount);
>
> - dev_set_drvdata(&rpdev->dev, data);
> rdev->dma_mask = &data->dma_mask;
> dma_set_mask_and_coherent(rdev, DMA_BIT_MASK(32));
> INIT_LIST_HEAD(&data->users);
> @@ -2440,6 +2439,7 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device
> *rpdev)
> idr_init(&data->ctx_idr);
> data->domain_id = domain_id;
> data->rpdev = rpdev;
> + dev_set_drvdata(&rpdev->dev, data);
>
> err = of_platform_populate(rdev->of_node, NULL, NULL, rdev);
> if (err)
> @@ -2513,6 +2513,9 @@ static int fastrpc_rpmsg_callback(struct rpmsg_device
> *rpdev, void *data,
> if (len < sizeof(*rsp))
> return -EINVAL;
>
> + if (!cctx)
> + return -ENODEV;
> +
> ctxid = ((rsp->ctx & FASTRPC_CTXID_MASK) >> 4);
>
> spin_lock_irqsave(&cctx->lock, flags);
> --
> 2.53.0
>
>
