Re: [PATCH 6/6] misc: fastrpc: Restrict untrusted app to attach to privileged PD
From: gregkh@xxxxxxxxxxxxxxxxxxx
Date: Thu Aug 15 2024 - 01:15:58 EST
On Thu, Aug 15, 2024 at 02:34:18AM +0000, Selvaraj, Joel (MU-Student) wrote:
> Hi Srinivas Kandagatla and Ekansh Gupta,
>
> On 6/28/24 06:45, srinivas.kandagatla@xxxxxxxxxx wrote:
> > From: Ekansh Gupta <quic_ekangupt@xxxxxxxxxxx>
> >
> > Untrusted application with access to only non-secure fastrpc device
> > node can attach to root_pd or static PDs if it can make the respective
> > init request. This can cause problems as the untrusted application
> > can send bad requests to root_pd or static PDs. Add changes to reject
> > attach to privileged PDs if the request is being made using non-secure
> > fastrpc device node.
> >
> > Fixes: 0871561055e6 ("misc: fastrpc: Add support for audiopd")
> > Cc: stable <stable@xxxxxxxxxx>
> > Signed-off-by: Ekansh Gupta <quic_ekangupt@xxxxxxxxxxx>
> > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> > ---
> > drivers/misc/fastrpc.c | 22 +++++++++++++++++++---
> > include/uapi/misc/fastrpc.h | 3 +++
> > 2 files changed, 22 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> > index 5680856c0fb8..a7a2bcedb37e 100644
> > --- a/drivers/misc/fastrpc.c
> > +++ b/drivers/misc/fastrpc.c
> > @@ -2087,6 +2087,16 @@ static int fastrpc_req_mem_map(struct fastrpc_user *fl, char __user *argp)
> > return err;
> > }
> >
> > +static int is_attach_rejected(struct fastrpc_user *fl)
> > +{
> > + /* Check if the device node is non-secure */
> > + if (!fl->is_secure_dev) {
> > + dev_dbg(&fl->cctx->rpdev->dev, "untrusted app trying to attach to privileged DSP PD\n");
> > + return -EACCES;
> > + }
> > + return 0;
> > +}
>
> This broke userspace for us. Sensors stopped working in SDM845 and other
> qcom SoC devices running postmarketOS. Trying to communicate with the
> fastrpc device just ends up with a permission denied error. This was
> previously working. I am not sure if this is intended. Here are my two
> observations:
>
> 1. if change the if condition to
>
> `if (!fl->is_secure_dev && fl->cctx->secure)`
>
> similar to how it's done in fastrpc's `is_session_rejected()` function,
> then it works. But I am not sure if this is an valid fix. But currently,
> fastrpc will simply deny access to all fastrpc device that contains the
> `qcom,non-secure-domain` dt property. Is that the intended change?
> Because I see a lot of adsp, cdsp and sdsp fastrpc nodes have that dt
> property.
>
> 2. In the `fastrpc_rpmsg_probe()` function, it is commented that,
>
> "Unsigned PD offloading is only supported on CDSP"
>
> Does this mean adsp and sdsp shouldn't have the `qcom,non-secure-domain`
> dt property? In fact, it was reported that removing this dt property and
> using the `/dev/fastrpc-sdsp-secure` node instead works fine too. Is
> this the correct way to fix it?
>
> I don't know much about fastrpc, just reporting the issue and guessing
> here. It would be really if this can be fixed before the stable release.
I will be glad to revert it, what was the git id for this in the tree
now?
thanks,
greg k-h