diff options
| -rw-r--r-- | drivers/char/hw_random/virtio-rng.c | 23 |
1 files changed, 21 insertions, 2 deletions
diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c index 0ce02d7e5048..5e83ffa105e4 100644 --- a/drivers/char/hw_random/virtio-rng.c +++ b/drivers/char/hw_random/virtio-rng.c @@ -7,6 +7,7 @@ #include <asm/barrier.h> #include <linux/err.h> #include <linux/hw_random.h> +#include <linux/nospec.h> #include <linux/scatterlist.h> #include <linux/spinlock.h> #include <linux/virtio.h> @@ -69,8 +70,26 @@ static void request_entropy(struct virtrng_info *vi) static unsigned int copy_data(struct virtrng_info *vi, void *buf, unsigned int size) { - size = min_t(unsigned int, size, vi->data_avail); - memcpy(buf, vi->data + vi->data_idx, size); + unsigned int idx, avail; + + /* + * vi->data_avail was set from the device-reported used.len and + * vi->data_idx was advanced by previous copy_data() calls. A + * malicious or buggy virtio-rng backend can drive either past + * sizeof(vi->data). Clamp at point of use and harden the index + * with array_index_nospec() so the memcpy() below cannot be + * steered into adjacent slab memory, including under + * speculation. + */ + avail = min_t(unsigned int, vi->data_avail, sizeof(vi->data)); + if (vi->data_idx >= avail) { + vi->data_avail = 0; + request_entropy(vi); + return 0; + } + size = min_t(unsigned int, size, avail - vi->data_idx); + idx = array_index_nospec(vi->data_idx, sizeof(vi->data)); + memcpy(buf, vi->data + idx, size); vi->data_idx += size; vi->data_avail -= size; if (vi->data_avail == 0) |