The link_status array was not large enough to read the Adjust Request
Post Cursor2 register. Adjust the size to include it. Found with a
-Warray-bounds build:
drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor':
drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds]
59 | return link_status[r - DP_LANE0_1_STATUS];
| ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status'
147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
| ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments")
Signed-off-by: Kees Cook <[email protected]>
---
v2: Fix missed array size change in intel_dp_check_mst_status()
---
drivers/gpu/drm/i915/display/intel_dp.c | 8 ++++----
include/drm/drm_dp_helper.h | 10 +++++++++-
2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 5a8206298691..97367afc7243 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -3647,17 +3647,17 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
for (;;) {
/*
- * The +2 is because DP_DPRX_ESI_LEN is 14, but we then
+ * The +10 is because while DP_DPRX_ESI_LEN is 14, we then
* pass in "esi+10" to drm_dp_channel_eq_ok(), which
- * takes a 6-byte array. So we actually need 16 bytes
- * here.
+ * takes a DP_LINK_STATUS_SIZE array. So we actually need
+ * 10 bytes more than DP_LINK_STATUS_SIZE.
*
* Somebody who knows what the limits actually are
* should check this, but for now this is at least
* harmless and avoids a valid compiler warning about
* using more of the array than we have allocated.
*/
- u8 esi[DP_DPRX_ESI_LEN+2] = {};
+ u8 esi[DP_LINK_STATUS_SIZE + 10] = {};
bool handled;
int retry;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 472dac376284..277643d2fe2c 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1517,7 +1517,15 @@ enum drm_dp_phy {
#define DP_MST_LOGICAL_PORT_0 8
#define DP_LINK_CONSTANT_N_VALUE 0x8000
-#define DP_LINK_STATUS_SIZE 6
+/*
+ * DPCD registers in link_status:
+ * Link Status: 0x202 through 0x204
+ * Sink Status: 0x205
+ * Adjust Request: 0x206 through 0x207
+ * Training Score: 0x208 through 0x20b
+ * AR Post Cursor2: 0x20c
+ */
+#define DP_LINK_STATUS_SIZE 11
bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
int lane_count);
bool drm_dp_clock_recovery_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
--
2.30.2
On Fri, Dec 03, 2021 at 01:25:17AM -0800, Kees Cook wrote:
> The link_status array was not large enough to read the Adjust Request
> Post Cursor2 register. Adjust the size to include it. Found with a
> -Warray-bounds build:
>
> drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor':
> drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds]
> 59 | return link_status[r - DP_LANE0_1_STATUS];
> | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status'
> 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments")
> Signed-off-by: Kees Cook <[email protected]>
> ---
> v2: Fix missed array size change in intel_dp_check_mst_status()
> ---
> drivers/gpu/drm/i915/display/intel_dp.c | 8 ++++----
> include/drm/drm_dp_helper.h | 10 +++++++++-
> 2 files changed, 13 insertions(+), 5 deletions(-)
This sounds very familiar and I vaguely recall typing up a patch like
that a long time ago. But I obviously failed because that never seems
to have made it upstream.
Or perhaps I'm misremembering and was thinking about this instead:
https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/338590/
Bonus points for adding that comment with background information on why
we need this.
Reviewed-by: Thierry Reding <[email protected]>
On Fri, Dec 03, 2021 at 04:28:56PM +0100, Thierry Reding wrote:
> On Fri, Dec 03, 2021 at 01:25:17AM -0800, Kees Cook wrote:
> > The link_status array was not large enough to read the Adjust Request
> > Post Cursor2 register. Adjust the size to include it. Found with a
> > -Warray-bounds build:
> >
> > drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor':
> > drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds]
> > 59 | return link_status[r - DP_LANE0_1_STATUS];
> > | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
> > drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status'
> > 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
> > | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments")
> > Signed-off-by: Kees Cook <[email protected]>
> > ---
> > v2: Fix missed array size change in intel_dp_check_mst_status()
> > ---
> > drivers/gpu/drm/i915/display/intel_dp.c | 8 ++++----
> > include/drm/drm_dp_helper.h | 10 +++++++++-
> > 2 files changed, 13 insertions(+), 5 deletions(-)
>
> This sounds very familiar and I vaguely recall typing up a patch like
> that a long time ago. But I obviously failed because that never seems
> to have made it upstream.
>
> Or perhaps I'm misremembering and was thinking about this instead:
>
> https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/338590/
Oh! Yeah, that's the same thing. Looks like that never made its way
upstream. :(
>
> Bonus points for adding that comment with background information on why
> we need this.
Thanks! Yeah, I needed to really convince myself everything added up and
made sense, and figured I should try to capture that research. ;)
> Reviewed-by: Thierry Reding <[email protected]>
Thanks!
-Kees
--
Kees Cook