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Message-ID: <87y23rlsmf.fsf@intel.com>
Date: Fri, 07 Jan 2022 12:58:32 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Kees Cook <keescook@...omium.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
dri-devel@...ts.freedesktop.org,
Thierry Reding <thierry.reding@...il.com>,
Jonathan Hunter <jonathanh@...dia.com>,
Philipp Zabel <p.zabel@...gutronix.de>,
Lyude Paul <lyude@...hat.com>, linux-kernel@...r.kernel.org,
linux-tegra@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] drm/dp: Remove common Post Cursor2 register handling
On Wed, 05 Jan 2022, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Jan 05, 2022 at 08:00:50PM +0200, Jani Nikula wrote:
>> On Wed, 05 Jan 2022, Kees Cook <keescook@...omium.org> wrote:
>> > The link_status array was not large enough to read the Adjust Request
>> > Post Cursor2 register, so remove the common helper function to avoid
>> > an OOB read, 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],
>> > | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> >
>> > Replace the only user of the helper with an open-coded fetch and decode,
>> > similar to drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c.
>> >
>> > Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments")
>> > Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
>> > Cc: Maxime Ripard <mripard@...nel.org>
>> > Cc: Thomas Zimmermann <tzimmermann@...e.de>
>> > Cc: David Airlie <airlied@...ux.ie>
>> > Cc: Daniel Vetter <daniel@...ll.ch>
>> > Cc: dri-devel@...ts.freedesktop.org
>> > Signed-off-by: Kees Cook <keescook@...omium.org>
>> > ---
>> > This is the alternative to:
>> > https://lore.kernel.org/lkml/20211203084354.3105253-1-keescook@chromium.org/
>> > ---
>> > drivers/gpu/drm/drm_dp_helper.c | 10 ----------
>> > drivers/gpu/drm/tegra/dp.c | 11 ++++++++++-
>> > include/drm/drm_dp_helper.h | 2 --
>> > 3 files changed, 10 insertions(+), 13 deletions(-)
>> >
>> > 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..f5535eb04c6b 100644
>> > --- a/drivers/gpu/drm/tegra/dp.c
>> > +++ b/drivers/gpu/drm/tegra/dp.c
>> > @@ -549,6 +549,15 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link,
>> > {
>> > struct drm_dp_link_train_set *adjust = &link->train.adjust;
>> > unsigned int i;
>> > + u8 post_cursor;
>> > + int err;
>> > +
>> > + err = drm_dp_dpcd_read(link->aux, DP_ADJUST_REQUEST_POST_CURSOR2,
>> > + &post_cursor, sizeof(post_cursor));
>>
>> There's a drm_dp_dpcd_readb() for the common 1-byte reads. Other than
>> that,
>>
>> Reviewed-by: Jani Nikula <jani.nikula@...el.com>
>
> Thanks!
>
>>
>> Though obviously that's not enough to actually merge to tegra.
>
> As in, "a review by Jani isn't sufficient to land via the tegra tree"?
Yeah. Or, in this case, via any tree, really.
> What should next steps be?
Get an ack from tegra and/or drm-misc maintainers. All the relevant
folks and lists are in the recipients already.
BR,
Jani.
>
> -Kees
>
>>
>> > + if (err < 0) {
>> > + DRM_ERROR("failed to read post_cursor2: %d\n", err);
>> > + post_cursor = 0;
>> > + }
>> >
>> > for (i = 0; i < link->lanes; i++) {
>> > adjust->voltage_swing[i] =
>> > @@ -560,7 +569,7 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link,
>> > DP_TRAIN_PRE_EMPHASIS_SHIFT;
>> >
>> > adjust->post_cursor[i] =
>> > - drm_dp_get_adjust_request_post_cursor(status, i);
>> > + (post_cursor >> (i << 1)) & 0x3;
>> > }
>> > }
>> >
>> > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
>> > index 472dac376284..fdf3cf6ccc02 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
>>
>> --
>> Jani Nikula, Intel Open Source Graphics Center
--
Jani Nikula, Intel Open Source Graphics Center
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