On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote:
> On Fri, 03 Dec 2021, Kees Cook <keescook@xxxxxxxxxxxx> 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 <keescook@xxxxxxxxxxxx>
>
> Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3
> published in 2014, and Tegra is the only user of
> drm_dp_get_adjust_request_post_cursor().
>
> Instead of bumping the link status read size from 6 to 11 for all
> drivers I'd much rather see some other (maybe Tegra specific) solution
> to this.
Hmmm... Well given this is currently non-functional on Tegra (and is an
OOB memory read), how about just removing it entirely?
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 23f9073bc473..c9528aa62c9c 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -144,16 +144,6 @@ u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE],
}
EXPORT_SYMBOL(drm_dp_get_adjust_tx_ffe_preset);
-u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
- unsigned int lane)
-{
- unsigned int offset = DP_ADJUST_REQUEST_POST_CURSOR2;
- u8 value = dp_link_status(link_status, offset);
-
- return (value >> (lane << 1)) & 0x3;
-}
-EXPORT_SYMBOL(drm_dp_get_adjust_request_post_cursor);
-
static int __8b10b_clock_recovery_delay_us(const struct drm_dp_aux *aux, u8 rd_interval)
{
if (rd_interval > 4)
diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c
index 70dfb7d1dec5..bb5bfa93950f 100644
--- a/drivers/gpu/drm/tegra/dp.c
+++ b/drivers/gpu/drm/tegra/dp.c
@@ -559,8 +559,7 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link,
drm_dp_get_adjust_request_pre_emphasis(status, i) >>
DP_TRAIN_PRE_EMPHASIS_SHIFT;
- adjust->post_cursor[i] =
- drm_dp_get_adjust_request_post_cursor(status, i);
+ adjust->post_cursor[i] = 0;
}
}
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 30359e434c3f..28378db676c8 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1528,8 +1528,6 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI
int lane);
u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE],
int lane);
-u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
- unsigned int lane);
#define DP_BRANCH_OUI_HEADER_SIZE 0xc
#define DP_RECEIVER_CAP_SIZE 0xf
Or maybe do a long link status read in Tegra only?
--
Kees Cook
