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Tue, 25 Aug 2026 11:29:06 +0000 (UTC) Received: from localhost (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 0232F1800643; Tue, 25 Aug 2026 11:29:03 +0000 (UTC) From: =?utf-8?q?Marc-Andr=C3=A9_Lureau?= Date: Tue, 25 Aug 2026 15:20:54 +0400 Subject: [GIT PULL 04/19] hw/display/qxl: validate primary surface stride against width MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260825-fixes-v1-4-c59e8a620836@redhat.com> References: <20260825-fixes-v1-0-c59e8a620836@redhat.com> In-Reply-To: <20260825-fixes-v1-0-c59e8a620836@redhat.com> To: qemu-devel@nongnu.org Cc: richard.henderson@linaro.org X-Developer-Signature: v=1; a=openpgp-sha256; l=10463; i=marcandre.lureau@redhat.com; h=from:subject:message-id; bh=4UDCl8lex+MxXuYGkgLc9J338hwBSKTVbnExSWrIGN8=; b=owEBbQKS/ZANAwAKAdro4Ql1lpzlAcsmYgBqjXrURBkt8KXzcL5On+NWHlnlNmSTvn7yx85h+ dBDs4hPI7mJAjMEAAEKAB0WIQSHqb2TP4fGBtJ29i3a6OEJdZac5QUCao161AAKCRDa6OEJdZac 5TPYD/40gWKCdMuMcUizGaS8rB79GY0psW7B/l/nfdLcpW9ksITYPVj1NCr6ZtrFcxbz5Z2mML5 c3ltBUMf1q/tkhffoRPTGXDY4b213O1a3pl8XYuNlWSGaVfj4nWgIiaM/QzLxjyH/sSQGzo4ud2 PZzQR3Aa6rA6Jgp6A3xTX3WtZDAS1Q3CSl7a2m30QsfoLb4aqofSE01+11oDdJMai55ZMnyEzUF fGvO0bniImdS8jrtmY03W91HK9GeQqVtyI53ffFZ6XKaff6ZrzTVGsaGx1T1Q/ONBKDG6yacSro TZzA1a+W+6MxxREplY8EkSJmcLFwgOZYHd5kF/ZPhmNw7ejOxukYdc4cIz1woaGJc/I1VgrF3yL TH5boKIPFjiO0efPpi4mGTu6xAmjHorNkgjl81Us9Fzc3uynnZcwYGDMuN3lj3yWSVPRB907edQ t/6uqCfJ/kCIajBtsQkpk1Y5GsbWKBxARxMZwX5KVU4Oscwm6+qEfkNdsDyXr1ppxcMYQRU9ymN +JIrnvIR4thcxAV0J+ZnS6+XePnDBxziJGnx8UIqmwZaNBA42EWqjPld8CPfZhLHuyajPnXvWND My6AzXgDniqr2iiU9Alq7iggyCqX/911UGGyza9PBTMltkBmhtcG5t7tF2RIj7O4dk8O60oFO1F 8T0bzK+UTVP9eLw== X-Developer-Key: i=marcandre.lureau@redhat.com; a=openpgp; fpr=87A9BD933F87C606D276F62DDAE8E10975969CE5 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=marcandre.lureau@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org The existing validation in qxl_create_guest_primary() checks that abs(stride) * height fits in vgamem_size and that stride is 4-byte aligned, but never checks that abs(stride) is large enough to hold one row of pixels for the declared width and format. A malicious guest can create a primary surface with a stride much smaller than width * bytes_per_pixel (e.g. stride=4 for a 64-wide 32bpp surface). The spice server rejects this via red_validate_surface(), but the return is void and QEMU unconditionally proceeds to set up the local rendering state. On the next display refresh, VNC or SDL reads width * bytes_pp per scanline from a region backed by only stride bytes per row, causing a host-side out-of-bounds read. Add three checks in qxl_create_guest_primary() before creating the surface: - reject unknown surface formats - reject zero width or height - reject surfaces where abs(stride) < width * bytes_per_pixel Also fix three related issues in qxl-render.c: - qxl_blit() used abs_stride to advance the dst pointer into the DisplaySurface, but when stride is negative the DisplaySurface is a packed buffer whose stride may be smaller. Use surface_stride() instead. - qxl_render_update_area_unlocked() uses guest_head0_width (set via QXL_IO_MONITORS_CONFIG_ASYNC) without validating it against abs_stride, bypassing the new validation. Clamp the effective width to abs_stride / bytes_pp to prevent out-of-bounds access while tolerating the normal transient where the monitor config arrives before the primary surface is resized to match. - Similarly, guest_head0_height bypasses qxl_create_guest_primary() validation. Without clamping, abs_stride * height can overrun vgamem_size, and the product can also overflow 32 bits (e.g. abs_stride=16 MiB, height=256 wraps to zero), defeating the qxl_phys2virt() bounds check. Clamp height to vgamem_size / abs_stride to prevent both. While touch it, fix some endianness issues. Fixes: CVE-2026-16271 Fixes: a19cbfb34642 ("spice: add qxl device") Fixes: 979f7ef8966b ("qxl: use guest_monitor_config for local renderer.") Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3637 Reported-by: huntr bubble Signed-off-by: Marc-Andre Lureau Reviewed-by: Akihiko Odaki Message-ID: <20260806094028.640676-1-marcandre.lureau@redhat.com> --- hw/display/qxl-render.c | 66 ++++++++++++++++++++++++++++++------------------- hw/display/qxl.c | 59 +++++++++++++++++++++++++++++++++++++++++++ hw/display/qxl.h | 2 ++ 3 files changed, 101 insertions(+), 26 deletions(-) diff --git a/hw/display/qxl-render.c b/hw/display/qxl-render.c index 4799c9e8befd..348ddba76890 100644 --- a/hw/display/qxl-render.c +++ b/hw/display/qxl-render.c @@ -27,6 +27,7 @@ static void qxl_blit(PCIQXLDevice *qxl, QXLRect *rect) { DisplaySurface *surface = qemu_console_surface(qxl->vga.con); + int dst_stride = surface_stride(surface); uint8_t *dst = surface_data(surface); uint8_t *src; int len, i; @@ -45,14 +46,14 @@ static void qxl_blit(PCIQXLDevice *qxl, QXLRect *rect) } else { src += rect->top * qxl->guest_primary.abs_stride; } - dst += rect->top * qxl->guest_primary.abs_stride; + dst += rect->top * dst_stride; src += rect->left * qxl->guest_primary.bytes_pp; dst += rect->left * qxl->guest_primary.bytes_pp; len = (rect->right - rect->left) * qxl->guest_primary.bytes_pp; for (i = rect->top; i < rect->bottom; i++) { memcpy(dst, src, len); - dst += qxl->guest_primary.abs_stride; + dst += dst_stride; src += qxl->guest_primary.qxl_stride; } } @@ -61,30 +62,13 @@ void qxl_render_resize(PCIQXLDevice *qxl) { QXLSurfaceCreate *sc = &qxl->guest_primary.surface; - qxl->guest_primary.qxl_stride = sc->stride; - qxl->guest_primary.abs_stride = abs(sc->stride); + qxl->guest_primary.qxl_stride = le32_to_cpu(sc->stride); + qxl->guest_primary.abs_stride = abs(qxl->guest_primary.qxl_stride); qxl->guest_primary.resized++; - switch (sc->format) { - case SPICE_SURFACE_FMT_16_555: - qxl->guest_primary.bytes_pp = 2; - qxl->guest_primary.bits_pp = 15; - break; - case SPICE_SURFACE_FMT_16_565: - qxl->guest_primary.bytes_pp = 2; - qxl->guest_primary.bits_pp = 16; - break; - case SPICE_SURFACE_FMT_32_xRGB: - case SPICE_SURFACE_FMT_32_ARGB: - qxl->guest_primary.bytes_pp = 4; - qxl->guest_primary.bits_pp = 32; - break; - default: - fprintf(stderr, "%s: unhandled format: %x\n", __func__, - qxl->guest_primary.surface.format); - qxl->guest_primary.bytes_pp = 4; - qxl->guest_primary.bits_pp = 32; - break; - } + /* fallback to default bpp if format is unknown */ + qxl_format_bpp(qxl, le32_to_cpu(sc->format), + &qxl->guest_primary.bytes_pp, + &qxl->guest_primary.bits_pp); } static void qxl_set_rect_to_surface(PCIQXLDevice *qxl, QXLRect *area) @@ -101,15 +85,45 @@ static void qxl_render_update_area_unlocked(PCIQXLDevice *qxl) DisplaySurface *surface; int width = qxl->guest_head0_width ?: qxl->guest_primary.surface.width; int height = qxl->guest_head0_height ?: qxl->guest_primary.surface.height; + uint64_t map_height; int i; + if (width <= 0 || height <= 0) { + goto end; + } + + if (qxl->guest_primary.bytes_pp > 0) { + int max_width = qxl->guest_primary.abs_stride + / qxl->guest_primary.bytes_pp; + width = MIN(width, max_width); + } + + if (qxl->guest_primary.qxl_stride < 0) { + /* qxl_blit() uses the primary height to find the first scanline. */ + height = MIN(height, (int)qxl->guest_primary.surface.height); + } + + if (qxl->guest_primary.abs_stride > 0) { + int max_height = qxl->vgamem_size / qxl->guest_primary.abs_stride; + height = MIN(height, max_height); + } + + /* + * height limits the visible update, while map_height is the guest memory + * span validated by qxl_phys2virt(). With a negative stride qxl_blit() + * addresses scanlines from the declared primary height, so a shorter + * monitor still requires validating the full primary surface. + */ + map_height = qxl->guest_primary.qxl_stride < 0 ? + qxl->guest_primary.surface.height : height; + if (qxl->guest_primary.resized) { qxl->guest_primary.resized = 0; qxl->guest_primary.data = qxl_phys2virt(qxl, qxl->guest_primary.surface.mem, MEMSLOT_GROUP_GUEST, qxl->guest_primary.abs_stride - * height); + * map_height); if (!qxl->guest_primary.data) { goto end; } diff --git a/hw/display/qxl.c b/hw/display/qxl.c index b7d871b9ee33..384b8767b8e6 100644 --- a/hw/display/qxl.c +++ b/hw/display/qxl.c @@ -1489,6 +1489,47 @@ static void qxl_create_guest_primary_complete(PCIQXLDevice *qxl) qxl_render_resize(qxl); } +/* + * Convert a SpiceSurfaceFormat to bytes per pixel and bits per pixel. + * + * Only valid for surface suitable for rendering. + */ +bool qxl_format_bpp(PCIQXLDevice *qxl, SpiceSurfaceFmt format, + uint32_t *bytes_pp, uint32_t *bits_pp) +{ + uint32_t bypp = 4; + uint32_t bipp = 32; + bool ret = true; + + switch (format) { + case SPICE_SURFACE_FMT_16_555: + bypp = 2; + bipp = 15; + break; + case SPICE_SURFACE_FMT_16_565: + bypp = 2; + bipp = 16; + break; + case SPICE_SURFACE_FMT_32_xRGB: + case SPICE_SURFACE_FMT_32_ARGB: + bypp = 4; + bipp = 32; + break; + default: + ret = false; + qxl_set_guest_bug(qxl, "%s: unhandled format: %x", __func__, format); + } + + if (bytes_pp != NULL) { + *bytes_pp = bypp; + } + if (bits_pp != NULL) { + *bits_pp = bipp; + } + + return ret; +} + static void qxl_create_guest_primary(PCIQXLDevice *qxl, int loadvm, qxl_async_io async) { @@ -1496,6 +1537,7 @@ static void qxl_create_guest_primary(PCIQXLDevice *qxl, int loadvm, QXLSurfaceCreate *sc = &qxl->guest_primary.surface; uint32_t requested_height = le32_to_cpu(sc->height); int requested_stride = le32_to_cpu(sc->stride); + uint32_t bytes_pp; if (requested_stride == INT32_MIN || abs(requested_stride) * (uint64_t)requested_height @@ -1532,6 +1574,23 @@ static void qxl_create_guest_primary(PCIQXLDevice *qxl, int loadvm, return; } + if (!qxl_format_bpp(qxl, surface.format, &bytes_pp, NULL)) { + return; + } + + if (surface.width == 0 || surface.height == 0) { + qxl_set_guest_bug(qxl, "%s: zero dimension %ux%u", + __func__, surface.width, surface.height); + return; + } + + if ((uint64_t)surface.width * bytes_pp > abs(surface.stride)) { + qxl_set_guest_bug(qxl, "%s: stride too small for width:" + " stride %d width %u bpp %u", + __func__, surface.stride, surface.width, bytes_pp); + return; + } + surface.mouse_mode = true; surface.group_id = MEMSLOT_GROUP_GUEST; if (loadvm) { diff --git a/hw/display/qxl.h b/hw/display/qxl.h index 48d664f77736..6f5b96fe86cc 100644 --- a/hw/display/qxl.h +++ b/hw/display/qxl.h @@ -181,6 +181,8 @@ void qxl_spice_oom(PCIQXLDevice *qxl); void qxl_spice_reset_memslots(PCIQXLDevice *qxl); void qxl_spice_reset_image_cache(PCIQXLDevice *qxl); void qxl_spice_reset_cursor(PCIQXLDevice *qxl); +bool qxl_format_bpp(PCIQXLDevice *qxl, SpiceSurfaceFmt format, + uint32_t *bytes_pp, uint32_t *bits_pp); /* qxl-logger.c */ int qxl_log_cmd_cursor(PCIQXLDevice *qxl, QXLCursorCmd *cmd, int group_id); -- 2.55.0.543.g5ebe2ebe4ea8