RE: [PATCH v5 1/2] drm/hyperv: validate resolution_count and fix WIN8 fallback
From: Michael Kelley <hidden>
Date: 2026-05-23 15:16:43
Also in:
dri-devel, lkml
From: Berkant Koc <redacted> 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 <redacted>
Assisted-by: Claude:claude-opus-4-7 berkoc-pipeline
Fixes: 76c56a5affeb ("drm/hyperv: Add DRM driver for hyperv synthetic video device")
Cc: stable@vger.kernel.org # 5.14+
Reviewed-by: Michael Kelley <redacted>I ran a basic smoke-test on my local Hyper-V instance. I can confirm that no error messages or failure were generated in the "good" case where the resolution_count from Hyper-V is valid. I did not simulate a bogus resolution_count and ensure it is detected. Tested-by: Michael Kelley <redacted>
quoted hunk ↗ jump to hunk
--- 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.cb/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