Michael S. Tsirkin
2022-Feb-23 15:15 UTC
[PATCH] vhost: validate range size before adding to iotlb
On Wed, Feb 23, 2022 at 07:48:18PM +0530, Anirudh Rayabharam wrote:> On Tue, Feb 22, 2022 at 06:21:50PM -0500, Michael S. Tsirkin wrote: > > On Tue, Feb 22, 2022 at 10:57:41PM +0530, Anirudh Rayabharam wrote: > > > On Tue, Feb 22, 2022 at 10:02:29AM -0500, Michael S. Tsirkin wrote: > > > > On Tue, Feb 22, 2022 at 03:11:07PM +0800, Jason Wang wrote: > > > > > On Tue, Feb 22, 2022 at 12:57 PM Anirudh Rayabharam <mail at anirudhrb.com> wrote: > > > > > > > > > > > > On Tue, Feb 22, 2022 at 10:50:20AM +0800, Jason Wang wrote: > > > > > > > On Tue, Feb 22, 2022 at 3:53 AM Anirudh Rayabharam <mail at anirudhrb.com> wrote: > > > > > > > > > > > > > > > > In vhost_iotlb_add_range_ctx(), validate the range size is non-zero > > > > > > > > before proceeding with adding it to the iotlb. > > > > > > > > > > > > > > > > Range size can overflow to 0 when start is 0 and last is (2^64 - 1). > > > > > > > > One instance where it can happen is when userspace sends an IOTLB > > > > > > > > message with iova=size=uaddr=0 (vhost_process_iotlb_msg). So, an > > > > > > > > entry with size = 0, start = 0, last = (2^64 - 1) ends up in the > > > > > > > > iotlb. Next time a packet is sent, iotlb_access_ok() loops > > > > > > > > indefinitely due to that erroneous entry: > > > > > > > > > > > > > > > > Call Trace: > > > > > > > > <TASK> > > > > > > > > iotlb_access_ok+0x21b/0x3e0 drivers/vhost/vhost.c:1340 > > > > > > > > vq_meta_prefetch+0xbc/0x280 drivers/vhost/vhost.c:1366 > > > > > > > > vhost_transport_do_send_pkt+0xe0/0xfd0 drivers/vhost/vsock.c:104 > > > > > > > > vhost_worker+0x23d/0x3d0 drivers/vhost/vhost.c:372 > > > > > > > > kthread+0x2e9/0x3a0 kernel/kthread.c:377 > > > > > > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > > > > > > > > </TASK> > > > > > > > > > > > > > > > > Reported by syzbot at: > > > > > > > > https://syzkaller.appspot.com/bug?extid=0abd373e2e50d704db87 > > > > > > > > > > > > > > > > Reported-by: syzbot+0abd373e2e50d704db87 at syzkaller.appspotmail.com > > > > > > > > Tested-by: syzbot+0abd373e2e50d704db87 at syzkaller.appspotmail.com > > > > > > > > Signed-off-by: Anirudh Rayabharam <mail at anirudhrb.com> > > > > > > > > --- > > > > > > > > drivers/vhost/iotlb.c | 6 ++++-- > > > > > > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > > > > > > > > > > > diff --git a/drivers/vhost/iotlb.c b/drivers/vhost/iotlb.c > > > > > > > > index 670d56c879e5..b9de74bd2f9c 100644 > > > > > > > > --- a/drivers/vhost/iotlb.c > > > > > > > > +++ b/drivers/vhost/iotlb.c > > > > > > > > @@ -53,8 +53,10 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb, > > > > > > > > void *opaque) > > > > > > > > { > > > > > > > > struct vhost_iotlb_map *map; > > > > > > > > + u64 size = last - start + 1; > > > > > > > > > > > > > > > > - if (last < start) > > > > > > > > + // size can overflow to 0 when start is 0 and last is (2^64 - 1). > > > > > > > > + if (last < start || size == 0) > > > > > > > > return -EFAULT; > > > > > > > > > > > > > > I'd move this check to vhost_chr_iter_write(), then for the device who > > > > > > > has its own msg handler (e.g vDPA) can benefit from it as well. > > > > > > > > > > > > Thanks for reviewing! > > > > > > > > > > > > I kept the check here thinking that all devices would benefit from it > > > > > > because they would need to call vhost_iotlb_add_range() to add an entry > > > > > > to the iotlb. Isn't that correct? > > > > > > > > > > Correct for now but not for the future, it's not guaranteed that the > > > > > per device iotlb message handler will use vhost iotlb. > > > > > > > > > > But I agree that we probably don't need to care about it too much now. > > > > > > > > > > > Do you see any other benefit in moving > > > > > > it to vhost_chr_iter_write()? > > > > > > > > > > > > One concern I have is that if we move it out some future caller to > > > > > > vhost_iotlb_add_range() might forget to handle this case. > > > > > > > > > > Yes. > > > > > > > > > > Rethink the whole fix, we're basically rejecting [0, ULONG_MAX] range > > > > > which seems a little bit odd. > > > > > > > > Well, I guess ideally we'd split this up as two entries - this kind of > > > > thing is after all one of the reasons we initially used first,last as > > > > the API - as opposed to first,size. > > > > > > IIUC, the APIs exposed to userspace accept first,size. > > > > Some of them. > > > > > > /* vhost vdpa IOVA range > > * @first: First address that can be mapped by vhost-vDPA > > * @last: Last address that can be mapped by vhost-vDPA > > */ > > struct vhost_vdpa_iova_range { > > __u64 first; > > __u64 last; > > }; > > Alright, I will split it into two entries. That doesn't fully address > the bug though. I would also need to validate size in vhost_chr_iter_write().Do you mean vhost_chr_write_iter?> > Should I do both in one patch or as a two patch series?I'm not sure why we need to do validation in vhost_chr_iter_write, hard to say without seeing the patch.> > > > but > > > > struct vhost_iotlb_msg { > > __u64 iova; > > __u64 size; > > __u64 uaddr; > > #define VHOST_ACCESS_RO 0x1 > > #define VHOST_ACCESS_WO 0x2 > > #define VHOST_ACCESS_RW 0x3 > > __u8 perm; > > #define VHOST_IOTLB_MISS 1 > > #define VHOST_IOTLB_UPDATE 2 > > #define VHOST_IOTLB_INVALIDATE 3 > > #define VHOST_IOTLB_ACCESS_FAIL 4 > > /* > > * VHOST_IOTLB_BATCH_BEGIN and VHOST_IOTLB_BATCH_END allow modifying > > * multiple mappings in one go: beginning with > > * VHOST_IOTLB_BATCH_BEGIN, followed by any number of > > * VHOST_IOTLB_UPDATE messages, and ending with VHOST_IOTLB_BATCH_END. > > * When one of these two values is used as the message type, the rest > > * of the fields in the message are ignored. There's no guarantee that > > * these changes take place automatically in the device. > > */ > > #define VHOST_IOTLB_BATCH_BEGIN 5 > > #define VHOST_IOTLB_BATCH_END 6 > > __u8 type; > > }; > > > > > > > > > Which means that > > > right now there is now way for userspace to map this range. So, is there > > > any value in not simply rejecting this range? > > > > > > > > > > > Anirudh, could you do it like this instead of rejecting? > > > > > > > > > > > > > I wonder if it's better to just remove > > > > > the map->size. Having a quick glance at the the user, I don't see any > > > > > blocker for this. > > > > > > > > > > Thanks > > > > > > > > I think it's possible but won't solve the bug by itself, and we'd need > > > > to review and fix all users - a high chance of introducing > > > > another regression. > > > > > > Agreed, I did a quick review of the usages and getting rid of size > > > didn't seem trivial. > > > > > > Thanks, > > > > > > - Anirudh. > > > > > > > And I think there's value of fitting under the > > > > stable rule of 100 lines with context. > > > > So sure, but let's fix the bug first. > > > > > > > > > > > > > > > > > > > > > > > > Thanks! > > > > > > > > > > > > - Anirudh. > > > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > if (iotlb->limit && > > > > > > > > @@ -69,7 +71,7 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb, > > > > > > > > return -ENOMEM; > > > > > > > > > > > > > > > > map->start = start; > > > > > > > > - map->size = last - start + 1; > > > > > > > > + map->size = size; > > > > > > > > map->last = last; > > > > > > > > map->addr = addr; > > > > > > > > map->perm = perm; > > > > > > > > -- > > > > > > > > 2.35.1 > > > > > > > > > > > > > > > > > > > > > > > > > > >