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Re: [PATCH v2] virtio: gracefully handle invalid region caches
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From: |
Michael S. Tsirkin |
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Subject: |
Re: [PATCH v2] virtio: gracefully handle invalid region caches |
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Date: |
Mon, 24 Feb 2020 08:37:29 -0500 |
On Mon, Feb 24, 2020 at 01:35:54PM +0000, Stefan Hajnoczi wrote:
> On Fri, Feb 07, 2020 at 10:46:19AM +0000, Stefan Hajnoczi wrote:
> > The virtqueue code sets up MemoryRegionCaches to access the virtqueue
> > guest RAM data structures. The code currently assumes that
> > VRingMemoryRegionCaches is initialized before device emulation code
> > accesses the virtqueue. An assertion will fail in
> > vring_get_region_caches() when this is not true. Device fuzzing found a
> > case where this assumption is false (see below).
> >
> > Virtqueue guest RAM addresses can also be changed from a vCPU thread
> > while an IOThread is accessing the virtqueue. This breaks the same
> > assumption but this time the caches could become invalid partway through
> > the virtqueue code. The code fetches the caches RCU pointer multiple
> > times so we will need to validate the pointer every time it is fetched.
> >
> > Add checks each time we call vring_get_region_caches() and treat invalid
> > caches as a nop: memory stores are ignored and memory reads return 0.
> >
> > The fuzz test failure is as follows:
> >
> > $ qemu -M pc -device virtio-blk-pci,id=drv0,drive=drive0,addr=4.0 \
> > -drive
> > if=none,id=drive0,file=null-co://,format=raw,auto-read-only=off \
> > -drive
> > if=none,id=drive1,file=null-co://,file.read-zeroes=on,format=raw \
> > -display none \
> > -qtest stdio
> > endianness
> > outl 0xcf8 0x80002020
> > outl 0xcfc 0xe0000000
> > outl 0xcf8 0x80002004
> > outw 0xcfc 0x7
> > write 0xe0000000 0x24
> > 0x00ffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffab5cffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffabffffffab0000000001
> > inb 0x4
> > writew 0xe000001c 0x1
> > write 0xe0000014 0x1 0x0d
> >
> > The following error message is produced:
> >
> > qemu-system-x86_64: /home/stefanha/qemu/hw/virtio/virtio.c:286:
> > vring_get_region_caches: Assertion `caches != NULL' failed.
> >
> > The backtrace looks like this:
> >
> > #0 0x00007ffff5520625 in raise () at /lib64/libc.so.6
> > #1 0x00007ffff55098d9 in abort () at /lib64/libc.so.6
> > #2 0x00007ffff55097a9 in _nl_load_domain.cold () at /lib64/libc.so.6
> > #3 0x00007ffff5518a66 in annobin_assert.c_end () at /lib64/libc.so.6
> > #4 0x00005555559073da in vring_get_region_caches (vq=<optimized out>) at
> > qemu/hw/virtio/virtio.c:286
> > #5 vring_get_region_caches (vq=<optimized out>) at
> > qemu/hw/virtio/virtio.c:283
> > #6 0x000055555590818d in vring_used_flags_set_bit (mask=1,
> > vq=0x5555575ceea0) at qemu/hw/virtio/virtio.c:398
> > #7 virtio_queue_split_set_notification (enable=0, vq=0x5555575ceea0) at
> > qemu/hw/virtio/virtio.c:398
> > #8 virtio_queue_set_notification (vq=vq@entry=0x5555575ceea0,
> > enable=enable@entry=0) at qemu/hw/virtio/virtio.c:451
> > #9 0x0000555555908512 in virtio_queue_set_notification
> > (vq=vq@entry=0x5555575ceea0, enable=enable@entry=0) at
> > qemu/hw/virtio/virtio.c:444
> > #10 0x00005555558c697a in virtio_blk_handle_vq (s=0x5555575c57e0,
> > vq=0x5555575ceea0) at qemu/hw/block/virtio-blk.c:775
> > #11 0x0000555555907836 in virtio_queue_notify_aio_vq (vq=0x5555575ceea0)
> > at qemu/hw/virtio/virtio.c:2244
> > #12 0x0000555555cb5dd7 in aio_dispatch_handlers
> > (ctx=ctx@entry=0x55555671a420) at util/aio-posix.c:429
> > #13 0x0000555555cb67a8 in aio_dispatch (ctx=0x55555671a420) at
> > util/aio-posix.c:460
> > #14 0x0000555555cb307e in aio_ctx_dispatch (source=<optimized out>,
> > callback=<optimized out>, user_data=<optimized out>) at util/async.c:260
> > #15 0x00007ffff7bbc510 in g_main_context_dispatch () at
> > /lib64/libglib-2.0.so.0
> > #16 0x0000555555cb5848 in glib_pollfds_poll () at util/main-loop.c:219
> > #17 os_host_main_loop_wait (timeout=<optimized out>) at
> > util/main-loop.c:242
> > #18 main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:518
> > #19 0x00005555559b20c9 in main_loop () at vl.c:1683
> > #20 0x0000555555838115 in main (argc=<optimized out>, argv=<optimized
> > out>, envp=<optimized out>) at vl.c:4441
> >
> > Reported-by: Alexander Bulekov <address@hidden>
> > Cc: Michael Tsirkin <address@hidden>
> > Cc: Cornelia Huck <address@hidden>
> > Cc: Paolo Bonzini <address@hidden>
> > Signed-off-by: Stefan Hajnoczi <address@hidden>
> > ---
> > An alternative solution is to keep the vring.caches pointer non-NULL all
> > the time so no checks are necessary. We would need to initialize it to
> > a VRingMemoryRegionCaches object that points to unassigned_mem. This
> > way virtio.c never hits NULL pointers and all memory loads/stores become
> > nop when caches are invalid.
> >
> > I think this solution is cleaner but couldn't see a reasonable way of
> > initializing MemoryRegionCache objects so that they point to a 64-bit
> > unassigned_mem MemoryRegion. Maybe someone who knows the memory API
> > better knows whether this is doable?
> >
> > Michael: We discussed changing vring.desc checks, but I think that's no
> > longer necessary with this patch. If a guest gets past a vring.desc
> > check then it can no longer trigger the assertion failure.
> > ---
> > hw/virtio/virtio.c | 99 ++++++++++++++++++++++++++++++++++++++++++----
> > 1 file changed, 91 insertions(+), 8 deletions(-)
>
> Ping?
Queued, thanks!
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 2c5410e981..00d444699d 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -282,15 +282,19 @@ static void vring_packed_flags_write(VirtIODevice
> > *vdev,
> > /* Called within rcu_read_lock(). */
> > static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQueue
> > *vq)
> > {
> > - VRingMemoryRegionCaches *caches = atomic_rcu_read(&vq->vring.caches);
> > - assert(caches != NULL);
> > - return caches;
> > + return atomic_rcu_read(&vq->vring.caches);
> > }
> > +
> > /* Called within rcu_read_lock(). */
> > static inline uint16_t vring_avail_flags(VirtQueue *vq)
> > {
> > VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
> > hwaddr pa = offsetof(VRingAvail, flags);
> > +
> > + if (!caches) {
> > + return 0;
> > + }
> > +
> > return virtio_lduw_phys_cached(vq->vdev, &caches->avail, pa);
> > }
> >
> > @@ -299,6 +303,11 @@ static inline uint16_t vring_avail_idx(VirtQueue *vq)
> > {
> > VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
> > hwaddr pa = offsetof(VRingAvail, idx);
> > +
> > + if (!caches) {
> > + return 0;
> > + }
> > +
> > vq->shadow_avail_idx = virtio_lduw_phys_cached(vq->vdev,
> > &caches->avail, pa);
> > return vq->shadow_avail_idx;
> > }
> > @@ -308,6 +317,11 @@ static inline uint16_t vring_avail_ring(VirtQueue *vq,
> > int i)
> > {
> > VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
> > hwaddr pa = offsetof(VRingAvail, ring[i]);
> > +
> > + if (!caches) {
> > + return 0;
> > + }
> > +
> > return virtio_lduw_phys_cached(vq->vdev, &caches->avail, pa);
> > }
> >
> > @@ -323,6 +337,11 @@ static inline void vring_used_write(VirtQueue *vq,
> > VRingUsedElem *uelem,
> > {
> > VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
> > hwaddr pa = offsetof(VRingUsed, ring[i]);
> > +
> > + if (!caches) {
> > + return;
> > + }
> > +
> > virtio_tswap32s(vq->vdev, &uelem->id);
> > virtio_tswap32s(vq->vdev, &uelem->len);
> > address_space_write_cached(&caches->used, pa, uelem,
> > sizeof(VRingUsedElem));
> > @@ -334,6 +353,11 @@ static uint16_t vring_used_idx(VirtQueue *vq)
> > {
> > VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
> > hwaddr pa = offsetof(VRingUsed, idx);
> > +
> > + if (!caches) {
> > + return 0;
> > + }
> > +
> > return virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
> > }
> >
> > @@ -342,8 +366,12 @@ static inline void vring_used_idx_set(VirtQueue *vq,
> > uint16_t val)
> > {
> > VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
> > hwaddr pa = offsetof(VRingUsed, idx);
> > - virtio_stw_phys_cached(vq->vdev, &caches->used, pa, val);
> > - address_space_cache_invalidate(&caches->used, pa, sizeof(val));
> > +
> > + if (caches) {
> > + virtio_stw_phys_cached(vq->vdev, &caches->used, pa, val);
> > + address_space_cache_invalidate(&caches->used, pa, sizeof(val));
> > + }
> > +
> > vq->used_idx = val;
> > }
> >
> > @@ -353,8 +381,13 @@ static inline void vring_used_flags_set_bit(VirtQueue
> > *vq, int mask)
> > VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
> > VirtIODevice *vdev = vq->vdev;
> > hwaddr pa = offsetof(VRingUsed, flags);
> > - uint16_t flags = virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
> > + uint16_t flags;
> >
> > + if (!caches) {
> > + return;
> > + }
> > +
> > + flags = virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
> > virtio_stw_phys_cached(vdev, &caches->used, pa, flags | mask);
> > address_space_cache_invalidate(&caches->used, pa, sizeof(flags));
> > }
> > @@ -365,8 +398,13 @@ static inline void
> > vring_used_flags_unset_bit(VirtQueue *vq, int mask)
> > VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
> > VirtIODevice *vdev = vq->vdev;
> > hwaddr pa = offsetof(VRingUsed, flags);
> > - uint16_t flags = virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
> > + uint16_t flags;
> >
> > + if (!caches) {
> > + return;
> > + }
> > +
> > + flags = virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
> > virtio_stw_phys_cached(vdev, &caches->used, pa, flags & ~mask);
> > address_space_cache_invalidate(&caches->used, pa, sizeof(flags));
> > }
> > @@ -381,6 +419,10 @@ static inline void vring_set_avail_event(VirtQueue
> > *vq, uint16_t val)
> > }
> >
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + return;
> > + }
> > +
> > pa = offsetof(VRingUsed, ring[vq->vring.num]);
> > virtio_stw_phys_cached(vq->vdev, &caches->used, pa, val);
> > address_space_cache_invalidate(&caches->used, pa, sizeof(val));
> > @@ -410,7 +452,11 @@ static void
> > virtio_queue_packed_set_notification(VirtQueue *vq, int enable)
> > VRingMemoryRegionCaches *caches;
> >
> > RCU_READ_LOCK_GUARD();
> > - caches = vring_get_region_caches(vq);
> > + caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + return;
> > + }
> > +
> > vring_packed_event_read(vq->vdev, &caches->used, &e);
> >
> > if (!enable) {
> > @@ -597,6 +643,10 @@ static int virtio_queue_packed_empty_rcu(VirtQueue *vq)
> > }
> >
> > cache = vring_get_region_caches(vq);
> > + if (!cache) {
> > + return 1;
> > + }
> > +
> > vring_packed_desc_read_flags(vq->vdev, &desc.flags, &cache->desc,
> > vq->last_avail_idx);
> >
> > @@ -777,6 +827,10 @@ static void virtqueue_packed_fill_desc(VirtQueue *vq,
> > }
> >
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + return;
> > + }
> > +
> > vring_packed_desc_write(vq->vdev, &desc, &caches->desc, head,
> > strict_order);
> > }
> >
> > @@ -949,6 +1003,10 @@ static void virtqueue_split_get_avail_bytes(VirtQueue
> > *vq,
> >
> > max = vq->vring.num;
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + goto err;
> > + }
> > +
> > while ((rc = virtqueue_num_heads(vq, idx)) > 0) {
> > MemoryRegionCache *desc_cache = &caches->desc;
> > unsigned int num_bufs;
> > @@ -1089,6 +1147,9 @@ static void
> > virtqueue_packed_get_avail_bytes(VirtQueue *vq,
> >
> > max = vq->vring.num;
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + goto err;
> > + }
> >
> > for (;;) {
> > unsigned int num_bufs = total_bufs;
> > @@ -1194,6 +1255,10 @@ void virtqueue_get_avail_bytes(VirtQueue *vq,
> > unsigned int *in_bytes,
> > }
> >
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + goto err;
> > + }
> > +
> > desc_size = virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED) ?
> > sizeof(VRingPackedDesc) :
> > sizeof(VRingDesc);
> > if (caches->desc.len < vq->vring.num * desc_size) {
> > @@ -1387,6 +1452,11 @@ static void *virtqueue_split_pop(VirtQueue *vq,
> > size_t sz)
> > i = head;
> >
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + virtio_error(vdev, "Region caches not initialized");
> > + goto done;
> > + }
> > +
> > if (caches->desc.len < max * sizeof(VRingDesc)) {
> > virtio_error(vdev, "Cannot map descriptor ring");
> > goto done;
> > @@ -1509,6 +1579,11 @@ static void *virtqueue_packed_pop(VirtQueue *vq,
> > size_t sz)
> > i = vq->last_avail_idx;
> >
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + virtio_error(vdev, "Region caches not initialized");
> > + goto done;
> > + }
> > +
> > if (caches->desc.len < max * sizeof(VRingDesc)) {
> > virtio_error(vdev, "Cannot map descriptor ring");
> > goto done;
> > @@ -1628,6 +1703,10 @@ static unsigned int
> > virtqueue_packed_drop_all(VirtQueue *vq)
> > VRingPackedDesc desc;
> >
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + return 0;
> > + }
> > +
> > desc_cache = &caches->desc;
> >
> > virtio_queue_set_notification(vq, 0);
> > @@ -2412,6 +2491,10 @@ static bool virtio_packed_should_notify(VirtIODevice
> > *vdev, VirtQueue *vq)
> > VRingMemoryRegionCaches *caches;
> >
> > caches = vring_get_region_caches(vq);
> > + if (!caches) {
> > + return false;
> > + }
> > +
> > vring_packed_event_read(vdev, &caches->avail, &e);
> >
> > old = vq->signalled_used;
> > --
> > 2.24.1
> >