From: Michal Hocko <mhocko@xxxxxxxx> vhost driver relies on copy_from_user/get_user from a kernel thread. This makes it impossible to reap the memory of an oom victim which shares mm with the vhost kernel thread because it could see a zero page unexpectedly and theoretically make an incorrect decision visible outside of the killed task context. To quote Michael S. Tsirkin: : Getting an error from __get_user and friends is handled gracefully. : Getting zero instead of a real value will cause userspace : memory corruption. Make sure that each place which can read from userspace is annotated properly and it uses copy_from_user_mm, __get_user_mm resp. copy_from_iter_mm. Each will get the target mm as an argument and it performs a pessimistic check to rule out that the oom_reaper could possibly unmap the particular page. __oom_reap_task then just needs to mark the mm as unstable before it unmaps any page. This is a preparatory patch without any functional changes because the oom reaper doesn't touch mm shared with kthreads yet. Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> --- drivers/vhost/scsi.c | 2 +- drivers/vhost/vhost.c | 18 +++++++++--------- include/linux/sched.h | 1 + include/linux/uaccess.h | 22 ++++++++++++++++++++++ include/linux/uio.h | 10 ++++++++++ mm/oom_kill.c | 8 ++++++++ 6 files changed, 51 insertions(+), 10 deletions(-) diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c index 0e6fd556c982..2c8dc0b9a21f 100644 --- a/drivers/vhost/scsi.c +++ b/drivers/vhost/scsi.c @@ -932,7 +932,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq) */ iov_iter_init(&out_iter, WRITE, vq->iov, out, out_size); - ret = copy_from_iter(req, req_size, &out_iter); + ret = copy_from_iter_mm(vq->dev->mm, req, req_size, &out_iter); if (unlikely(ret != req_size)) { vq_err(vq, "Faulted on copy_from_iter\n"); vhost_scsi_send_bad_target(vs, vq, head, out); diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 669fef1e2bb6..71a754a0fe7e 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1212,7 +1212,7 @@ int vhost_vq_init_access(struct vhost_virtqueue *vq) r = -EFAULT; goto err; } - r = __get_user(last_used_idx, &vq->used->idx); + r = __get_user_mm(vq->dev->mm, last_used_idx, &vq->used->idx); if (r) goto err; vq->last_used_idx = vhost16_to_cpu(vq, last_used_idx); @@ -1328,7 +1328,7 @@ static int get_indirect(struct vhost_virtqueue *vq, i, count); return -EINVAL; } - if (unlikely(copy_from_iter(&desc, sizeof(desc), &from) != + if (unlikely(copy_from_iter_mm(vq->dev->mm, &desc, sizeof(desc), &from) != sizeof(desc))) { vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n", i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc); @@ -1392,7 +1392,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, /* Check it isn't doing very strange things with descriptor numbers. */ last_avail_idx = vq->last_avail_idx; - if (unlikely(__get_user(avail_idx, &vq->avail->idx))) { + if (unlikely(__get_user_mm(vq->dev->mm, avail_idx, &vq->avail->idx))) { vq_err(vq, "Failed to access avail idx at %p\n", &vq->avail->idx); return -EFAULT; @@ -1414,7 +1414,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, /* Grab the next descriptor number they're advertising, and increment * the index we've seen. */ - if (unlikely(__get_user(ring_head, + if (unlikely(__get_user_mm(vq->dev->mm, ring_head, &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) { vq_err(vq, "Failed to read head: idx %d address %p\n", last_avail_idx, @@ -1450,7 +1450,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, i, vq->num, head); return -EINVAL; } - ret = __copy_from_user(&desc, vq->desc + i, sizeof desc); + ret = __copy_from_user_mm(vq->dev->mm, &desc, vq->desc + i, sizeof desc); if (unlikely(ret)) { vq_err(vq, "Failed to get descriptor: idx %d addr %p\n", i, vq->desc + i); @@ -1622,7 +1622,7 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) { __virtio16 flags; - if (__get_user(flags, &vq->avail->flags)) { + if (__get_user_mm(dev->mm, flags, &vq->avail->flags)) { vq_err(vq, "Failed to get flags"); return true; } @@ -1636,7 +1636,7 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) if (unlikely(!v)) return true; - if (__get_user(event, vhost_used_event(vq))) { + if (__get_user_mm(dev->mm, event, vhost_used_event(vq))) { vq_err(vq, "Failed to get used event idx"); return true; } @@ -1678,7 +1678,7 @@ bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq) __virtio16 avail_idx; int r; - r = __get_user(avail_idx, &vq->avail->idx); + r = __get_user_mm(dev->mm, avail_idx, &vq->avail->idx); if (r) return false; @@ -1713,7 +1713,7 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) /* They could have slipped one in as we were doing that: make * sure it's written, then check again. */ smp_mb(); - r = __get_user(avail_idx, &vq->avail->idx); + r = __get_user_mm(dev->mm, avail_idx, &vq->avail->idx); if (r) { vq_err(vq, "Failed to check avail idx at %p: %d\n", &vq->avail->idx, r); diff --git a/include/linux/sched.h b/include/linux/sched.h index befdcc1cde3c..ff5102adb0c4 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -513,6 +513,7 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_RECALC_UPROBES 20 /* MMF_HAS_UPROBES can be wrong */ #define MMF_OOM_REAPED 21 /* mm has been already reaped */ #define MMF_OOM_NOT_REAPABLE 22 /* mm couldn't be reaped */ +#define MMF_UNSTABLE 23 /* mm is unstable for copy_from_user */ #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK) diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 349557825428..a327d5362581 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -76,6 +76,28 @@ static inline unsigned long __copy_from_user_nocache(void *to, #endif /* ARCH_HAS_NOCACHE_UACCESS */ /* + * A safe variant of __get_user for for use_mm() users to have a + * gurantee that the address space wasn't reaped in the background + */ +#define __get_user_mm(mm, x, ptr) \ +({ \ + int ___gu_err = __get_user(x, ptr); \ + if (!___gu_err && test_bit(MMF_UNSTABLE, &mm->flags)) \ + ___gu_err = -EFAULT; \ + ___gu_err; \ +}) + +/* similar to __get_user_mm */ +static inline __must_check long __copy_from_user_mm(struct mm_struct *mm, + void *to, const void __user * from, unsigned long n) +{ + long ret = __copy_from_user(to, from, n); + if ((ret >= 0) && test_bit(MMF_UNSTABLE, &mm->flags)) + return -EFAULT; + return ret; +} + +/* * probe_kernel_read(): safely attempt to read from a location * @dst: pointer to the buffer that shall take the data * @src: address to read from diff --git a/include/linux/uio.h b/include/linux/uio.h index 1b5d1cd796e2..4be6b24003d8 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -9,6 +9,7 @@ #ifndef __LINUX_UIO_H #define __LINUX_UIO_H +#include <linux/sched.h> #include <linux/kernel.h> #include <uapi/linux/uio.h> @@ -84,6 +85,15 @@ size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes, struct iov_iter *i); size_t copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i); size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i); + +static inline size_t copy_from_iter_mm(struct mm_struct *mm, void *addr, + size_t bytes, struct iov_iter *i) +{ + size_t ret = copy_from_iter(addr, bytes, i); + if (!IS_ERR_VALUE(ret) && test_bit(MMF_UNSTABLE, &mm->flags)) + return -EFAULT; + return ret; +} size_t copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i); size_t iov_iter_zero(size_t bytes, struct iov_iter *); unsigned long iov_iter_alignment(const struct iov_iter *i); diff --git a/mm/oom_kill.c b/mm/oom_kill.c index b2210b6c38ba..38a0cd32c01b 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -492,6 +492,14 @@ static bool __oom_reap_task(struct task_struct *tsk) goto unlock_oom; } + /* + * Tell all users of get_user_mm/copy_from_user_mm that the content + * is no longer stable. No barriers really needed because unmapping + * should imply barriers already and the reader would hit a page fault + * if it stumbled over a reaped memory. + */ + set_bit(MMF_UNSTABLE, &mm->flags); + ret = true; tlb_gather_mmu(&tlb, mm, 0, -1); for (vma = mm->mmap ; vma; vma = vma->vm_next) { -- 2.8.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>