linux-kernel - Re: [PATCH 6/6] misc: fastrpc: Restrict untrusted app to attach to privileged PD

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Message-ID: <362eea30-7b6d-4cd5-aed9-88c0d014dd91@gmail.com>
Date: Thu, 15 Aug 2024 03:35:13 -0500
From: Joel Selvaraj <joelselvaraj.oss@...il.com>
To: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc: "srinivas.kandagatla@...aro.org" <srinivas.kandagatla@...aro.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Ekansh Gupta <quic_ekangupt@...cinc.com>, stable <stable@...nel.org>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH 6/6] misc: fastrpc: Restrict untrusted app to attach to
 privileged PD

Hi greg k-h,

The git commit id is: bab2f5e8fd5d2f759db26b78d9db57412888f187

But I am bit hesitant if we should revert it because there is a CVE 
attached to it: https://ubuntu.com/security/CVE-2024-41024

Also, I am ok with changing userspace if it's necessary. It would be 
nice if the authors can clarify the ideal fix here.

Regards,
Joel Selvaraj

On 8/15/24 00:15, gregkh@...uxfoundation.org wrote:
> 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@...aro.org wrote:
>>> From: Ekansh Gupta <quic_ekangupt@...cinc.com>
>>>
>>> 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@...nel.org>
>>> Signed-off-by: Ekansh Gupta <quic_ekangupt@...cinc.com>
>>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
>>> ---
>>>    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