linux-kernel - Re: [PATCH v3 7/9] misc: fastrpc: Restrict untrusted app to attach to privileged PD

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Date: Fri, 31 May 2024 10:48:04 +0100
From: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To: Ekansh Gupta <quic_ekangupt@...cinc.com>, linux-arm-msm@...r.kernel.org
Cc: gregkh@...uxfoundation.org, quic_bkumar@...cinc.com,
 linux-kernel@...r.kernel.org, quic_chennak@...cinc.com,
 stable <stable@...nel.org>
Subject: Re: [PATCH v3 7/9] misc: fastrpc: Restrict untrusted app to attach to
 privileged PD



On 30/05/2024 11:20, Ekansh Gupta wrote:
> 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>
> ---
>   drivers/misc/fastrpc.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index d9d9f889e39e..73fa0e536cf9 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -1344,6 +1344,11 @@ static int fastrpc_init_create_static_process(struct fastrpc_user *fl,
>   	} inbuf;
>   	u32 sc;
>   
> +	if (!fl->is_secure_dev) {
> +		dev_dbg(&fl->cctx->rpdev->dev, "untrusted app trying to attach to privileged DSP PD\n");
> +		return -EACCES;
> +	}

Please move these checks to fastrpc_device_ioctl which makes it clear 
that these are only supported with secure device nodes.

I would also prefer this to be documented in the the uapi headers.


--srini
> +
>   	args = kcalloc(FASTRPC_CREATE_STATIC_PROCESS_NARGS, sizeof(*args), GFP_KERNEL);
>   	if (!args)
>   		return -ENOMEM;
> @@ -1769,6 +1774,11 @@ static int fastrpc_init_attach(struct fastrpc_user *fl, int pd)
>   	int tgid = fl->tgid;
>   	u32 sc;
>   
> +	if (!fl->is_secure_dev) {
> +		dev_dbg(&fl->cctx->rpdev->dev, "untrusted app trying to attach to privileged DSP PD\n");
> +		return -EACCES;
> +	}
> +
>   	args[0].ptr = (u64)(uintptr_t) &tgid;
>   	args[0].length = sizeof(tgid);
>   	args[0].fd = -1;