Am 22.11.2017 um 17:34 hat Paolo Bonzini geschrieben: > On 22/11/2017 16:33, Deepa Srinivasan wrote: > > Starting qemu with the following arguments causes qemu to segfault: > > ... -device lsi,id=lsi0 -drive > > file=iscsi:<...>,format=raw,if=none,node-name= > > iscsi1 -device scsi-block,bus=lsi0.0,id=<...>,drive=iscsi1 > > > > This patch fixes blk_aio_ioctl() so it does not pass stack addresses to > > blk_aio_ioctl_entry() which may be invoked after blk_aio_ioctl() returns. > > More > > details about the bug follow. > > > > blk_aio_ioctl() invokes blk_aio_prwv() with blk_aio_ioctl_entry as the > > coroutine parameter. blk_aio_prwv() ultimately calls aio_co_enter(). > > > > When blk_aio_ioctl() is executed from within a coroutine context (e.g. > > iscsi_bh_cb()), aio_co_enter() adds the coroutine (blk_aio_ioctl_entry) to > > the current coroutine's wakeup queue. blk_aio_ioctl() then returns. > > > > When blk_aio_ioctl_entry() executes later, it accesses an invalid pointer: > > .... > > BlkRwCo *rwco = &acb->rwco; > > > > rwco->ret = blk_co_ioctl(rwco->blk, rwco->offset, > > rwco->qiov->iov[0].iov_base); <--- qiov is > > invalid > > here > > ... > > > > In the case when blk_aio_ioctl() is called from a non-coroutine context, > > blk_aio_ioctl_entry() executes immediately. But if bdrv_co_ioctl() calls > > qemu_coroutine_yield(), blk_aio_ioctl() will return. When the coroutine > > execution is complete, control returns to blk_aio_ioctl_entry() after the > > call > > to blk_co_ioctl(). There is no invalid reference after this point, but the > > function is still holding on to invalid pointers. > > > > The fix is to allocate memory for the QEMUIOVector and struct iovec as part > > of > > the request struct which the IO buffer is part of. The memory for this > > struct is > > guaranteed to be valid till the AIO is completed. > > > > Signed-off-by: Deepa Srinivasan <deepa.sriniva...@oracle.com> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com> > > Reviewed-by: Mark Kanda <mark.ka...@oracle.com> > > --- > > block/block-backend.c | 13 ++----------- > > hw/block/virtio-blk.c | 9 ++++++++- > > hw/scsi/scsi-disk.c | 10 +++++++++- > > hw/scsi/scsi-generic.c | 9 ++++++++- > > include/sysemu/block-backend.h | 2 +- > > 5 files changed, 28 insertions(+), 15 deletions(-) > > > > diff --git a/block/block-backend.c b/block/block-backend.c > > index baef8e7..c275827 100644 > > --- a/block/block-backend.c > > +++ b/block/block-backend.c > > @@ -1472,19 +1472,10 @@ static void blk_aio_ioctl_entry(void *opaque) > > blk_aio_complete(acb); > > } > > > > -BlockAIOCB *blk_aio_ioctl(BlockBackend *blk, unsigned long int req, void > > *buf, > > +BlockAIOCB *blk_aio_ioctl(BlockBackend *blk, unsigned long int req, > > QEMUIOVector *qiov, > > BlockCompletionFunc *cb, void *opaque) > > I think this is not the best way to fix the bug, because it adds extra > unnecessary code in the callers. > > Perhaps you can change BlkRwCo's "qiov" field to "void *buf" and the > same for blk_aio_prwv's "qiov" argument? > > Then the QEMUIOVector is not needed at all, and blk_co_ioctl can just > use rwco->buf.
But the same struct is used for read and write requests that do use an actual QEMUIOVector and not just a linear buffer. Kevin
