On Wed, May 10, 2023 at 09:04:44AM -0700, Lorenzo Stoakes wrote: > On Wed, May 10, 2023 at 03:15:51PM +0100, Mark Rutland wrote: > > Hi, > > > > On Sun, Apr 30, 2023 at 09:19:17PM +0100, Lorenzo Stoakes wrote: > > > We may still have inconsistent input parameters even if we choose not to > > > merge and the vma_merge() invariant checks are useful for checking this > > > with no production runtime cost (these are only relevant when > > > CONFIG_DEBUG_VM is specified). > > > > > > Therefore, perform these checks regardless of whether we merge. > > > > > > This is relevant, as a recent issue (addressed in commit "mm/mempolicy: > > > Correctly update prev when policy is equal on mbind") in the mbind logic > > > was only picked up in the 6.2.y stable branch where these assertions are > > > performed prior to determining mergeability. > > > > > > Had this remained the same in mainline this issue may have been picked up > > > faster, so moving forward let's always check them. > > > > > > Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > > > --- > > > mm/mmap.c | 10 +++++----- > > > 1 file changed, 5 insertions(+), 5 deletions(-) > > > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > > index 5522130ae606..13678edaa22c 100644 > > > --- a/mm/mmap.c > > > +++ b/mm/mmap.c > > > @@ -960,17 +960,17 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > > > merge_next = true; > > > } > > > > > > + /* Verify some invariant that must be enforced by the caller. */ > > > + VM_WARN_ON(prev && addr <= prev->vm_start); > > > + VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end)); > > > + VM_WARN_ON(addr >= end); > > > + > > > > I'm seeing this fire a lot when fuzzing v6.4-rc1 on arm64 using Syzkaller. > > > > Thanks, from the line I suspect addr != curr->vm_start, but need to look > into the repro, at lsf/mm so a bit time lagged :) No problem; FWIW I can confirm your theory, the reproducer is causing: addr > curr->vm_start ... confirmed the the following hack, log below. | diff --git a/mm/mmap.c b/mm/mmap.c | index 13678edaa22c..2cdebba15719 100644 | --- a/mm/mmap.c | +++ b/mm/mmap.c | @@ -961,9 +961,21 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, | } | | /* Verify some invariant that must be enforced by the caller. */ | - VM_WARN_ON(prev && addr <= prev->vm_start); | - VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end)); | - VM_WARN_ON(addr >= end); | + VM_WARN(prev && addr <= prev->vm_start, | + "addr = 0x%016lx, prev->vm_start = 0x%016lx\n", | + addr, prev->vm_start); | + | + VM_WARN(curr && addr != curr->vm_start, | + "addr = 0x%016lx, curr->vm_start = 0x%016lx\n", | + addr, curr->vm_start); | + | + VM_WARN(curr && addr > curr->vm_end, | + "addr = 0x%016lx, curr->vm_end = 0x%016lx\n", | + addr, curr->vm_end); | + | + VM_WARN(addr >= end, | + "addr = 0x%016lx, end = 0x%016lx\n", | + addr, end); | | if (!merge_prev && !merge_next) | return NULL; /* Not mergeable. */ ... with that applied, running the reproducer results in: | addr = 0x0000ffff99dc2000, curr->vm_start = 0x0000ffff99db2000 | WARNING: CPU: 0 PID: 163 at mm/mmap.c:968 vma_merge+0x3d4/0x1260 ... i.e. addr > curr->vm_start Thanks, Mark.
