Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
Pre-existing issues: - [Critical] Integer overflows in framebuffer creation and cursor command submission cause a Guest-to-Host Out-Of-Bounds Read. - [High] Missing Error Handling / NULL Pointer Dereference in `vmw_cursor_plane_prepare_fb`. - [High] State Confusion in `vmw_cursor_plane_atomic_check` allows bypassing legacy cursor dimension checks, leading to a massive kernel heap Out-Of-Bounds read. -- --- Patch [1]: [PATCH v2] drm/vmwgfx: Treat zero SVGA_REG_CURSOR_MAX_DIMENSION as unset --- commit fc08a38eba647596145d861cab4214687c5ce5ce Author: fausten <[email protected]> drm/vmwgfx: Treat zero SVGA_REG_CURSOR_MAX_DIMENSION as unset This commit treats a reported SVGA_REG_CURSOR_MAX_DIMENSION of 0 as "not implemented" and skips the cursor dimension check in that case. This restores the pre-existing behaviour for VMware Fusion guests (SVGA version 2) where the cursor previously did not show up. > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c > b/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c > index d1e7df5001903..fbdd23ecb2b4b 100644 > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c [ ... ] > @@ -748,8 +750,10 @@ int vmw_cursor_plane_atomic_check(struct drm_plane > *plane, > u32 cursor_max_dim = > vmw_read(vmw, SVGA_REG_CURSOR_MAX_DIMENSION); > > - if (new_state->crtc_w > cursor_max_dim || > - new_state->crtc_h > cursor_max_dim) { > + /* Some SVGA implementations (e.g. VMware Fusion) report 0 > here. */ > + if (cursor_max_dim && > + (new_state->crtc_w > cursor_max_dim || > + new_state->crtc_h > cursor_max_dim)) { [Severity: High] This isn't a bug introduced by this patch, but does the cursor plane code handle BO mapping failures safely? In drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c:vmw_cursor_plane_prepare_fb(), the return value of vmw_bo_map_and_cache_size() is cast to void, ignoring potential mapping failures: (void)vmw_bo_map_and_cache_size(bo, size); If this mapping fails, bo->map.virtual remains NULL. Later, in vmw_cursor_plane_atomic_update(), vmw_send_define_cursor_cmd() unconditionally copies to the command buffer using the unvalidated image pointer: memcpy(&cmd[1], image, image_size); Could this cause a NULL pointer dereference and kernel panic if memory pressure causes the mapping to fail? [Severity: High] This is a pre-existing issue, but does skipping this dimension check expose a state confusion bug that could lead to an out-of-bounds read? In drivers/gpu/drm/vmwgfx/vmwgfx_cursor_plane.c:vmw_cursor_plane_atomic_check(), update_type is evaluated using vmw_cursor_update_type(vmw, vps). At this point, vps->uo contains stale state from the previous commit, as it isn't updated until vmw_cursor_plane_prepare_fb(). If userspace commits a BO-backed cursor (GB_ONLY), and then in a subsequent commit submits a Surface-backed cursor (LEGACY) with huge dimensions (e.g., 512x512), atomic_check will evaluate the type as GB_ONLY. Since this patch skips the dimension check when cursor_max_dim == 0, the huge dimensions are accepted. When prepare_fb() runs, vps->uo is updated and the type correctly becomes LEGACY. Finally, in vmw_send_define_cursor_cmd(), the memcpy() reads width * height * 4 bytes from the 16KB legacy surface->snooper.image buffer: memcpy(&cmd[1], image, image_size); Could this result in a massive out-of-bounds read of the kernel heap being sent to the hypervisor? [Severity: Critical] This is a pre-existing issue, but does bypassing this check when cursor_max_dim == 0 expose integer overflows that can cause a guest-to-host out-of-bounds read? If userspace creates a framebuffer with massive dimensions (e.g., 32768x32768), the calculation in drivers/gpu/drm/vmwgfx/vmwgfx_kms.c:vmw_kms_new_framebuffer_bo() overflows 32 bits: requested_size = mode_cmd->height * mode_cmd->pitches[0]; if (unlikely(requested_size > bo->tbo.base.size)) { This overflow to 0 allows creating a massive framebuffer with a 1-page BO. Because this patch removes the dimension limit for cursor_max_dim == 0, the large cursor dimensions are accepted. When vmw_send_define_cursor_cmd() prepares the command: const u32 image_size = width * height * sizeof(*image); const u32 cmd_size = sizeof(*cmd) + image_size; image_size overflows to 0, resulting in only sizeof(*cmd) bytes being allocated in the command FIFO. The hypervisor receives the command specifying a 32768x32768 cursor but no pixel data follows in the FIFO. Will this cause the hypervisor to read 4GB out-of-bounds from the command FIFO? > drm_warn(&vmw->drm, > "Cursor dimensions (%d, %d) exceed device max > %u\n", > new_state->crtc_w, new_state->crtc_h, -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
