[PATCH v2 0/2] misc: fastrpc: Fixes for issues in userspace

[PATCH v2 0/2] misc: fastrpc: Fixes for issues in userspace

[Richard Acayan]

Changes since v1 (20230130222716.7016-1-mailingradian@gmail.com):
 - use /* */ for comments (2/2)
 - exclude demonstration from final commit message (2/2)
 - accumulate review tags (1-2/2)

Hi everyone,

I've been playing around a bit with the FastRPC ioctl interface on the
Pixel 3a with some device tree patches. I was testing on a device tree
that caused the ADSP to crash every 10 seconds, and the inconvenience
caused by related bugs encouraged me to write a few fixes. A
demonstration is provided in patch 2.

Please enjoy and review these patches for better userspace while remote
processors crash.

Richard Acayan (2):
  misc: fastrpc: return -EPIPE to invocations on device removal
  misc: fastrpc: reject new invocations during device removal

 drivers/misc/fastrpc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

-- 
2.40.0

[PATCH v2 1/2] misc: fastrpc: return -EPIPE to invocations on device removal

[Richard Acayan]

The return value is initialized as -1, or -EPERM. The completion of an
invocation implies that the return value is set appropriately, but
"Permission denied" does not accurately describe the outcome of the
invocation. Set the invocation's return value to a more appropriate
"Broken pipe", as the cleanup breaks the driver's connection with rpmsg.

Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
Signed-off-by: Richard Acayan <mailingradian@gmail.com>
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
---
 drivers/misc/fastrpc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index f48466960f1b..20c035af373a 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -2337,8 +2337,10 @@ static void fastrpc_notify_users(struct fastrpc_user *user)
 	struct fastrpc_invoke_ctx *ctx;
 
 	spin_lock(&user->lock);
-	list_for_each_entry(ctx, &user->pending, node)
+	list_for_each_entry(ctx, &user->pending, node) {
+		ctx->retval = -EPIPE;
 		complete(&ctx->work);
+	}
 	spin_unlock(&user->lock);
 }
 
-- 
2.40.0

[PATCH v2 2/2] misc: fastrpc: reject new invocations during device removal

[Richard Acayan]

The channel's rpmsg object allows new invocations to be made. After old
invocations are already interrupted, the driver shouldn't try to invoke
anymore. Invalidating the rpmsg at the end of the driver removal
function makes it easy to cause a race condition in userspace. Even
closing a file descriptor before the driver finishes its cleanup can
cause an invocation via fastrpc_release_current_dsp_process() and
subsequent timeout.

Invalidate the channel before the invocations are interrupted to make
sure that no invocations can be created to hang after the device closes.

Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
Signed-off-by: Richard Acayan <mailingradian@gmail.com>
---
Demonstration of the bug as performed on a Google Pixel 3a with
devicetree patches:

	#include <fcntl.h>
	#include <misc/fastrpc.h>
	#include <stdint.h>
	#include <stdio.h>
	#include <string.h>
	#include <sys/ioctl.h>
	#include <unistd.h>

	static int remotectl_open(int fd,
				  const char *name,
				  uint32_t *handle)
	{
		struct fastrpc_invoke invoke;
		struct fastrpc_invoke_args args[4];
		struct {
			uint32_t namelen;
			uint32_t errlen;
		} in;
		struct {
			uint32_t handle;
			uint32_t err;
		} out;
		char errstr[256];
		int ret;

		// Remoteproc expects to receive a null terminator
		in.namelen = strlen(name) + 1;
		in.errlen = 256;

		args[0].ptr = (__u64) &in;
		args[0].length = sizeof(in);
		args[0].fd = -1;

		args[1].ptr = (__u64) name;
		args[1].length = in.namelen;
		args[1].fd = -1;

		args[2].ptr = (__u64) &out;
		args[2].length = sizeof(out);
		args[2].fd = -1;

		args[3].ptr = (__u64) errstr;
		args[3].length = 256;
		args[3].fd = -1;

		invoke.handle = 0;
		invoke.sc = 0x00020200;
		invoke.args = (__u64) args;

		ret = ioctl(fd, FASTRPC_IOCTL_INVOKE, (__u64) &invoke);

		if (!ret)
			*handle = out.handle;

		return ret;
	}

	int main()
	{
		struct fastrpc_init_create_static create;
		uint32_t handle;
		int fd, ret;

		fd = open("/dev/fastrpc-adsp", O_RDWR);
		if (fd == -1) {
			perror("Could not open /dev/fastrpc-adsp");
			return 1;
		}

		ret = ioctl(fd, FASTRPC_IOCTL_INIT_ATTACH_SNS, NULL);
		if (ret) {
			perror("Could not attach to sensorspd");
			goto close_dev;
		}

		/*
		 * Under normal circumstances, the remote processor
		 * would request a file from a different client, and
		 * quickly find out that there is no such file. When
		 * this other client is not running, this procedure call
		 * conveniently waits for the ADSP to crash.
		 */
		ret = remotectl_open(fd, "a", &handle);
		if (ret == -1)
			perror("Could not open CHRE interface");

	close_dev:
		// This takes 10 seconds
		printf("Closing file descriptor\n");
		close(fd);
		printf("Closed file descriptor\n");

		return 0;
	}
---
 drivers/misc/fastrpc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 20c035af373a..f4116ce7805a 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -2351,7 +2351,9 @@ static void fastrpc_rpmsg_remove(struct rpmsg_device *rpdev)
 	struct fastrpc_user *user;
 	unsigned long flags;
 
+	/* No invocations past this point */
 	spin_lock_irqsave(&cctx->lock, flags);
+	cctx->rpdev = NULL;
 	list_for_each_entry(user, &cctx->users, user)
 		fastrpc_notify_users(user);
 	spin_unlock_irqrestore(&cctx->lock, flags);
@@ -2370,7 +2372,6 @@ static void fastrpc_rpmsg_remove(struct rpmsg_device *rpdev)
 
 	of_platform_depopulate(&rpdev->dev);
 
-	cctx->rpdev = NULL;
 	fastrpc_channel_ctx_put(cctx);
 }
 
-- 
2.40.0

Re: [PATCH v2 0/2] misc: fastrpc: Fixes for issues in userspace

[Srinivas Kandagatla]

On Mon, 27 Mar 2023 17:02:16 -0400, Richard Acayan wrote:
> Changes since v1 (20230130222716.7016-1-mailingradian@gmail.com):
>  - use /* */ for comments (2/2)
>  - exclude demonstration from final commit message (2/2)
>  - accumulate review tags (1-2/2)
> 
> Hi everyone,
> 
> [...]

Applied, thanks!

[1/2] misc: fastrpc: return -EPIPE to invocations on device removal
      commit: 578b3c7d15e65770a9b6317343a523e58f97d037
[2/2] misc: fastrpc: reject new invocations during device removal
      commit: 3a1f192ad1b46a2d783f54f1008e25d81d42587c

Best regards,
-- 
Srinivas Kandagatla <srinivas.kandagatla@linaro.org>