From 612db9c2a5551cc8e275ded6e7d1ae83be6d6d3c Mon Sep 17 00:00:00 2001
From: Douglas Anderson <dianders@chromium.org>
Date: Thu, 14 Dec 2023 12:37:51 -0800
Subject: drm/bridge: parade-ps8640: Never store more than msg->size bytes in
AUX xfer
Git-commit: 3164c8a70073d43629b4e11e083d3d2798f7750f
Patch-mainline: v6.7
References: jsc#PED-3527 jsc#PED-5475 jsc#PED-6068 jsc#PED-6070 jsc#PED-6116 jsc#PED-6120 jsc#PED-5065 jsc#PED-5477 jsc#PED-5511 jsc#PED-6041 jsc#PED-6069 jsc#PED-6071
While testing, I happened to notice a random crash that looked like:
Kernel panic - not syncing: stack-protector:
Kernel stack is corrupted in: drm_dp_dpcd_probe+0x120/0x120
Analysis of drm_dp_dpcd_probe() shows that we pass in a 1-byte buffer
(allocated on the stack) to the aux->transfer() function. Presumably
if the aux->transfer() writes more than one byte to this buffer then
we're in a bad shape.
Dropping into kgdb, I noticed that "aux->transfer" pointed at
ps8640_aux_transfer().
Reading through ps8640_aux_transfer(), I can see that there are cases
where it could write more bytes to msg->buffer than were specified by
msg->size. This could happen if the hardware reported back something
bogus to us. Let's fix this so we never write more than msg->size
bytes. We'll still read all the bytes from the hardware just in case
the hardware requires it since the aux transfer data comes through an
auto-incrementing register.
NOTE: I have no actual way to reproduce this issue but it seems likely
this is what was happening in the crash I looked at.
Fixes: 13afcdd7277e ("drm/bridge: parade-ps8640: Add support for AUX channel")
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231214123752.v3.1.I9d1afcaad76a3e2c0ca046dc4adbc2b632c22eda@changeid
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/bridge/parade-ps8640.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
index 8161b1a1a4b1..d264b80d909d 100644
--- a/drivers/gpu/drm/bridge/parade-ps8640.c
+++ b/drivers/gpu/drm/bridge/parade-ps8640.c
@@ -330,11 +330,12 @@ static ssize_t ps8640_aux_transfer_msg(struct drm_dp_aux *aux,
return ret;
}
- buf[i] = data;
+ if (i < msg->size)
+ buf[i] = data;
}
}
- return len;
+ return min(len, msg->size);
}
static ssize_t ps8640_aux_transfer(struct drm_dp_aux *aux,
--
2.43.0