Re: [PATCH v4] virtio-gpu: use g_try_malloc to avoid guest-triggered abort

On 2026/08/03 20:00, [email protected] wrote:
> From: Marc-André Lureau <[email protected]>
> 
> Use g_try_malloc/g_try_new0 for guest-controlled allocation, so failure
> returns an error to the guest rather than crashing the host (glib
> behaviour).
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3898
> Signed-off-by: Marc-André Lureau <[email protected]>
> ---
> Based-on: <[email protected]> ("[PATCH] vhost-user-gpu: fix integer overflow in buffer allocation")
> v4:
>   - unmap the inflight dma map on failure
>   - fix optional addr handling
> ---
>   contrib/vhost-user-gpu/vhost-user-gpu.c | 25 ++++++++++-----
>   contrib/vhost-user-gpu/virgl.c          |  6 +++-
>   contrib/vhost-user-gpu/vugbm.c          |  5 ++-
>   hw/display/virtio-gpu-rutabaga.c        | 14 +++++++--
>   hw/display/virtio-gpu-virgl.c           |  6 +++-
>   hw/display/virtio-gpu.c                 | 42 ++++++++++++++++++-------
>   6 files changed, 74 insertions(+), 24 deletions(-)
> 
> diff --git a/contrib/vhost-user-gpu/vhost-user-gpu.c b/contrib/vhost-user-gpu/vhost-user-gpu.c
> index ee9858c397ce..0fd115300425 100644
> --- a/contrib/vhost-user-gpu/vhost-user-gpu.c
> +++ b/contrib/vhost-user-gpu/vhost-user-gpu.c
> @@ -487,7 +487,7 @@ vg_create_mapping_iov(VuGpu *g,
>                         struct virtio_gpu_ctrl_command *cmd,
>                         struct iovec **iov)
>   {
> -    struct virtio_gpu_mem_entry *ents;
> +    g_autofree struct virtio_gpu_mem_entry *ents = NULL;
>       size_t esize, s;
>       int i;
>   
> @@ -498,17 +498,22 @@ vg_create_mapping_iov(VuGpu *g,
>       }
>   
>       esize = sizeof(*ents) * ab->nr_entries;
> -    ents = g_malloc(esize);
> +    ents = g_try_malloc(esize);
> +    if (!ents && esize) {
> +        return -1;
> +    }
>       s = iov_to_buf(cmd->elem.out_sg, cmd->elem.out_num,
>                      sizeof(*ab), ents, esize);
>       if (s != esize) {
>           g_critical("%s: command data size incorrect %zu vs %zu",
>                      __func__, s, esize);
> -        g_free(ents);
>           return -1;
>       }
>   
> -    *iov = g_new0(struct iovec, ab->nr_entries);
> +    *iov = g_try_new0(struct iovec, ab->nr_entries);
> +    if (!*iov && ab->nr_entries) {
> +        return -1;
> +    }
>       for (i = 0; i < ab->nr_entries; i++) {
>           uint64_t len = ents[i].length;
>           (*iov)[i].iov_len = ents[i].length;
> @@ -517,12 +522,10 @@ vg_create_mapping_iov(VuGpu *g,
>               g_critical("%s: resource %d element %d",
>                          __func__, ab->resource_id, i);
>               g_free(*iov);
> -            g_free(ents);
>               *iov = NULL;
>               return -1;
>           }
>       }
> -    g_free(ents);
>       return 0;
>   }
>   
> @@ -828,8 +831,14 @@ vg_resource_flush(VuGpu *g,
>                   PIXMAN_FORMAT_BPP(pixman_image_get_format(res->image)) / 8;
>               size_t size = width * height * bpp;
>   
> -            void *p = g_malloc(VHOST_USER_GPU_HDR_SIZE +
> -                               sizeof(VhostUserGpuUpdate) + size);
> +            void *p = g_try_malloc(VHOST_USER_GPU_HDR_SIZE +
> +                                   sizeof(VhostUserGpuUpdate) + size);
> +            if (!p) {
> +                pixman_region_fini(&region);
> +                pixman_region_fini(&finalregion);
> +                cmd->error = VIRTIO_GPU_RESP_ERR_OUT_OF_MEMORY;
> +                break;
> +            }
>               VhostUserGpuMsg *msg = p;
>               msg->request = VHOST_USER_GPU_UPDATE;
>               msg->size = sizeof(VhostUserGpuUpdate) + size;
> diff --git a/contrib/vhost-user-gpu/virgl.c b/contrib/vhost-user-gpu/virgl.c
> index 550fd03bf5c4..20bae57d0fe4 100644
> --- a/contrib/vhost-user-gpu/virgl.c
> +++ b/contrib/vhost-user-gpu/virgl.c
> @@ -209,7 +209,11 @@ virgl_cmd_submit_3d(VuGpu *g,
>           return;
>       }
>   
> -    buf = g_malloc(cs.size);
> +    buf = g_try_malloc(cs.size);
> +    if (!buf && cs.size) {
> +        cmd->error = VIRTIO_GPU_RESP_ERR_OUT_OF_MEMORY;
> +        return;
> +    }
>       s = iov_to_buf(cmd->elem.out_sg, cmd->elem.out_num,
>                      sizeof(cs), buf, cs.size);
>       if (s != cs.size) {
> diff --git a/contrib/vhost-user-gpu/vugbm.c b/contrib/vhost-user-gpu/vugbm.c
> index 710d54529779..e2d8385fd857 100644
> --- a/contrib/vhost-user-gpu/vugbm.c
> +++ b/contrib/vhost-user-gpu/vugbm.c
> @@ -13,7 +13,10 @@
>   static bool
>   mem_alloc_bo(struct vugbm_buffer *buf)
>   {
> -    buf->mmap = g_malloc((uint64_t)buf->width * buf->height * 4);
> +    buf->mmap = g_try_malloc((uint64_t)buf->width * buf->height * 4);
> +    if (!buf->mmap && buf->width && buf->height) {
> +        return false;
> +    }
>       buf->stride = buf->width * 4;
>       return true;
>   }
> diff --git a/hw/display/virtio-gpu-rutabaga.c b/hw/display/virtio-gpu-rutabaga.c
> index e28aad94eead..60f64d9a8fa7 100644
> --- a/hw/display/virtio-gpu-rutabaga.c
> +++ b/hw/display/virtio-gpu-rutabaga.c
> @@ -360,10 +360,20 @@ rutabaga_cmd_submit_3d(VirtIOGPU *g,
>           return;
>       }
>   
> -    buf = g_new0(uint8_t, cs.size);
> +    buf = g_try_new0(uint8_t, cs.size);
> +    if (!buf && cs.size) {
> +        cmd->error = VIRTIO_GPU_RESP_ERR_OUT_OF_MEMORY;
> +        return;
> +    }
>       s = iov_to_buf(cmd->elem.out_sg, cmd->elem.out_num,
>                      sizeof(cs), buf, cs.size);
> -    CHECK(s == cs.size, cmd);
> +    if (s != cs.size) {
> +        qemu_log_mask(LOG_GUEST_ERROR,
> +                      "%s: size mismatch (%zu/%u)\n",
> +                      __func__, s, cs.size);
> +        cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER;
> +        return;
> +    }
>   
>       rutabaga_cmd.ctx_id = cs.hdr.ctx_id;
>       rutabaga_cmd.cmd = buf;
> diff --git a/hw/display/virtio-gpu-virgl.c b/hw/display/virtio-gpu-virgl.c
> index d9e5b0110497..028ab776df6a 100644
> --- a/hw/display/virtio-gpu-virgl.c
> +++ b/hw/display/virtio-gpu-virgl.c
> @@ -615,7 +615,11 @@ static void virgl_cmd_submit_3d(VirtIOGPU *g,
>           return;
>       }
>   
> -    buf = g_malloc(cs.size);
> +    buf = g_try_malloc(cs.size);
> +    if (!buf && cs.size) {
> +        cmd->error = VIRTIO_GPU_RESP_ERR_OUT_OF_MEMORY;
> +        return;
> +    }
>       s = iov_to_buf(cmd->elem.out_sg, cmd->elem.out_num,
>                      sizeof(cs), buf, cs.size);
>       if (s != cs.size) {
> diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
> index c707f1f516ea..c97622115d46 100644
> --- a/hw/display/virtio-gpu.c
> +++ b/hw/display/virtio-gpu.c
> @@ -882,7 +882,10 @@ int virtio_gpu_create_mapping_iov(VirtIOGPU *g,
>       }
>   
>       esize = sizeof(*ents) * nr_entries;
> -    ents = g_malloc(esize);
> +    ents = g_try_malloc(esize);

The udmabuf path still aborts on a guest-amplified allocation in 
virtio_gpu_create_udmabuf(). RESOURCE_CREATE_BLOB reaches it immediately 
after this new fallible mapping allocation; attach-backing does 
likewise. Because dma_memory_map() can split each guest entry,
res->iov_cnt is not bounded by the 16384-entry limit. The IOV/address 
arrays can succeed, followed by g_malloc0(8 + 24 * res->iov_cnt) 
aborting under memory pressure.

Regards,
Akihiko Odaki

> +    if (!ents && esize) {
> +        return -1;
> +    }
>       s = iov_to_buf(cmd->elem.out_sg, cmd->elem.out_num,
>                      offset, ents, esize);
>       if (s != esize) {
> @@ -903,6 +906,7 @@ int virtio_gpu_create_mapping_iov(VirtIOGPU *g,
>           hwaddr len;
>           void *map;
>   
> +        /* TODO: a common DMA map SG helper */
>           do {
>               len = l;
>               map = dma_memory_map(VIRTIO_DEVICE(g)->dma_as, a, &len,
> @@ -911,20 +915,27 @@ int virtio_gpu_create_mapping_iov(VirtIOGPU *g,
>               if (!map) {
>                   qemu_log_mask(LOG_GUEST_ERROR, "%s: failed to map MMIO memory for"
>                                 " element %d\n", __func__, e);
> -                virtio_gpu_cleanup_mapping_iov(g, *iov, v);
> -                g_free(ents);
> -                *iov = NULL;
> -                if (addr) {
> -                    g_free(*addr);
> -                    *addr = NULL;
> -                }
> -                return -1;
> +                goto err;
>               }
>   
>               if (!(v % 16)) {
> -                *iov = g_renew(struct iovec, *iov, v + 16);
> +                struct iovec *new_iov;
> +                new_iov = g_try_renew(struct iovec, *iov, v + 16);
> +                if (!new_iov) {
> +                    dma_memory_unmap(VIRTIO_DEVICE(g)->dma_as, map, len,
> +                                     DMA_DIRECTION_TO_DEVICE, len);
> +                    goto err;
> +                }
> +                *iov = new_iov;
>                   if (addr) {
> -                    *addr = g_renew(uint64_t, *addr, v + 16);
> +                    uint64_t *new_addr;
> +                    new_addr = g_try_renew(uint64_t, *addr, v + 16);
> +                    if (!new_addr) {
> +                        dma_memory_unmap(VIRTIO_DEVICE(g)->dma_as, map, len,
> +                                         DMA_DIRECTION_TO_DEVICE, len);
> +                        goto err;
> +                    }
> +                    *addr = new_addr;
>                   }
>               }
>               (*iov)[v].iov_base = map;
> @@ -942,6 +953,15 @@ int virtio_gpu_create_mapping_iov(VirtIOGPU *g,
>   
>       g_free(ents);
>       return 0;
> +
> +err:
> +    virtio_gpu_cleanup_mapping_iov(g, *iov, v);
> +    *iov = NULL;
> +    if (addr) {
> +        g_clear_pointer(addr, g_free);
> +    }
> +    g_free(ents);
> +    return -1;
>   }
>   
>   void virtio_gpu_cleanup_mapping_iov(VirtIOGPU *g,