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From:   Gerd Hoffmann <kraxel@redhat.com>
To:     dri-devel@lists.freedesktop.org
Cc:     Gerd Hoffmann <kraxel@redhat.com>,
        Gustavo Padovan <gustavo@padovan.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        linux-kernel@vger.kernel.org (open list)
Subject: [PATCH] drm: refuse ADDFB2 ioctl for broken bigendian drivers
Date:   Thu,  6 Sep 2018 09:28:50 +0200
Message-Id: <20180906072850.11150-1-kraxel@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Drivers must set the quirk_addfb_prefer_host_byte_order quirk to make
the drm_mode_addfb() compat code work correctly on bigendian machines.

If they don't they interpret pixel_format values incorrectly for bug
compatibility, which in turn implies the ADDFB2 ioctl does not work
correctly then.  So block it to make userspace fallback to ADDFB.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 drivers/gpu/drm/drm_ioctl.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index ea10e9a26a..08e48bda23 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -469,6 +469,29 @@ static int drm_copy_field(char __user *buf, size_t *buf_len, const char *value)
 	return 0;
 }
 
+static int drm_mode_addfb2_check(struct drm_device *dev,
+				 void *data, struct drm_file *file_priv)
+{
+#ifdef __BIG_ENDIAN
+	if (!dev->mode_config.quirk_addfb_prefer_host_byte_order) {
+		/*
+		 * Drivers must set the
+		 * quirk_addfb_prefer_host_byte_order quirk to make
+		 * the drm_mode_addfb() compat code work correctly on
+		 * bigendian machines.
+		 *
+		 * If they don't they interpret pixel_format values
+		 * incorrectly for bug compatibility, which in turn
+		 * implies the ADDFB2 ioctl does not work correctly
+		 * then.  So block it to make userspace fallback to
+		 * ADDFB.
+		 */
+		return -EINVAL;
+	}
+#endif
+	return drm_mode_addfb2(dev, data, file_priv);
+}
+
 /*
  * Get version information
  *
@@ -645,7 +668,7 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETPROPBLOB, drm_mode_getblob_ioctl, DRM_UNLOCKED),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETFB, drm_mode_getfb, DRM_UNLOCKED),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_ADDFB, drm_mode_addfb_ioctl, DRM_UNLOCKED),
-	DRM_IOCTL_DEF(DRM_IOCTL_MODE_ADDFB2, drm_mode_addfb2, DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_IOCTL_MODE_ADDFB2, drm_mode_addfb2_check, DRM_UNLOCKED),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_RMFB, drm_mode_rmfb_ioctl, DRM_UNLOCKED),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_PAGE_FLIP, drm_mode_page_flip_ioctl, DRM_MASTER|DRM_UNLOCKED),
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_DIRTYFB, drm_mode_dirtyfb_ioctl, DRM_MASTER|DRM_UNLOCKED),
-- 
2.9.3