RE: [PATCH v3 1/2] drm/hyperv: validate resolution_count and fix WIN8 fallback

2026-05-21 Thread Michael Kelley 
From: Berkant Koc  Sent: Tuesday, May 19, 2026 1:08 PM
> 
> A SYNTHVID_RESOLUTION_RESPONSE with resolution_count > 64 walks past
> the supported_resolution[SYNTHVID_MAX_RESOLUTION_COUNT] array in the
> parse loop. Bound resolution_count against the array size, folded
> into the existing zero-check.
> 
> When the WIN10 resolution probe fails, the caller in
> hyperv_connect_vsp() left hv->screen_*_max / preferred_* unpopulated,
> which sets mode_config.max_width / max_height to 0 and makes
> drm_internal_framebuffer_create() reject every userspace framebuffer
> with -EINVAL. The pre-WIN10 branch had the same gap for
> preferred_width / preferred_height. Use a single post-probe fallback
> guarded by screen_width_max == 0 so both paths converge on the WIN8
> defaults.
> 
> Signed-off-by: Berkant Koc 
> Assisted-by: Claude:claude-opus-4-7 berkoc-pipeline
> Fixes: 76c56a5affeb ("drm/hyperv: Add DRM driver for hyperv synthetic video 
> device")
> Cc: [email protected] # 5.14+
> ---
>  drivers/gpu/drm/hyperv/hyperv_drm_proto.c | 13 ++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> index 051ecc526..c3d0ff229 100644
> --- a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> +++ b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
> @@ -391,8 +391,11 @@ static int hyperv_get_supported_resolution(struct 
> hv_device
> *hdev)
>   return -ETIMEDOUT;
>   }
> 
> - if (msg->resolution_resp.resolution_count == 0) {
> - drm_err(dev, "No supported resolutions\n");
> + if (msg->resolution_resp.resolution_count == 0 ||
> + msg->resolution_resp.resolution_count >
> + SYNTHVID_MAX_RESOLUTION_COUNT) {
> + drm_err(dev, "Invalid resolution count: %d\n",
> + msg->resolution_resp.resolution_count);
>   return -ENODEV;
>   }
> 
> @@ -508,9 +511,13 @@ int hyperv_connect_vsp(struct hv_device *hdev)
>   ret = hyperv_get_supported_resolution(hdev);
>   if (ret)
>   drm_err(dev, "Failed to get supported resolution from 
> host, use default\n");
> - } else {
> + }
> +
> + if (!hv->screen_width_max) {
>   hv->screen_width_max = SYNTHVID_WIDTH_WIN8;
>   hv->screen_height_max = SYNTHVID_HEIGHT_WIN8;
> + hv->preferred_width = SYNTHVID_WIDTH_WIN8;
> + hv->preferred_height = SYNTHVID_HEIGHT_WIN8;
>   }
> 
>   hv->mmio_megabytes = hdev->channel->offermsg.offer.mmio_megabytes;
> --
> 2.47.3
> 

Looks good to me.

Reviewed-by: Michael Kelley

[PATCH v3 1/2] drm/hyperv: validate resolution_count and fix WIN8 fallback

2026-05-19 Thread Berkant Koc 
A SYNTHVID_RESOLUTION_RESPONSE with resolution_count > 64 walks past
the supported_resolution[SYNTHVID_MAX_RESOLUTION_COUNT] array in the
parse loop. Bound resolution_count against the array size, folded
into the existing zero-check.

When the WIN10 resolution probe fails, the caller in
hyperv_connect_vsp() left hv->screen_*_max / preferred_* unpopulated,
which sets mode_config.max_width / max_height to 0 and makes
drm_internal_framebuffer_create() reject every userspace framebuffer
with -EINVAL. The pre-WIN10 branch had the same gap for
preferred_width / preferred_height. Use a single post-probe fallback
guarded by screen_width_max == 0 so both paths converge on the WIN8
defaults.

Signed-off-by: Berkant Koc 
Assisted-by: Claude:claude-opus-4-7 berkoc-pipeline
Fixes: 76c56a5affeb ("drm/hyperv: Add DRM driver for hyperv synthetic video 
device")
Cc: [email protected] # 5.14+
---
 drivers/gpu/drm/hyperv/hyperv_drm_proto.c | 13 ++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c 
b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
index 051ecc526..c3d0ff229 100644
--- a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
@@ -391,8 +391,11 @@ static int hyperv_get_supported_resolution(struct 
hv_device *hdev)
return -ETIMEDOUT;
}
 
-   if (msg->resolution_resp.resolution_count == 0) {
-   drm_err(dev, "No supported resolutions\n");
+   if (msg->resolution_resp.resolution_count == 0 ||
+   msg->resolution_resp.resolution_count >
+   SYNTHVID_MAX_RESOLUTION_COUNT) {
+   drm_err(dev, "Invalid resolution count: %d\n",
+   msg->resolution_resp.resolution_count);
return -ENODEV;
}
 
@@ -508,9 +511,13 @@ int hyperv_connect_vsp(struct hv_device *hdev)
ret = hyperv_get_supported_resolution(hdev);
if (ret)
drm_err(dev, "Failed to get supported resolution from 
host, use default\n");
-   } else {
+   }
+
+   if (!hv->screen_width_max) {
hv->screen_width_max = SYNTHVID_WIDTH_WIN8;
hv->screen_height_max = SYNTHVID_HEIGHT_WIN8;
+   hv->preferred_width = SYNTHVID_WIDTH_WIN8;
+   hv->preferred_height = SYNTHVID_HEIGHT_WIN8;
}
 
hv->mmio_megabytes = hdev->channel->offermsg.offer.mmio_megabytes;
-- 
2.47.3