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Wed, 10 May 2023 09:26:10 -0700 (PDT) Date: Wed, 10 May 2023 09:26:10 -0700 From: Lorenzo Stoakes To: Mark Rutland Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , "Liam R . Howlett" , Vlastimil Babka Subject: Re: [PATCH] mm/mmap/vma_merge: always check invariants Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2F1911C001D X-Stat-Signature: 94ksuy1hj7nfwfgqnekhjc1f3rs6k3fh X-HE-Tag: 1683735972-813113 X-HE-Meta: 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 F5lf7ZHx 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 10, 2023 at 05:17:49PM +0100, Mark Rutland wrote: > 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 > > > > --- > > > > 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. Awesome thanks for that! Just been firing up qemu to do this. Cases 5-8 should really have addr == curr->vm_start, I wonder if it's another case but curr is being set incorrectly, it should in theory not be the case. (See [1] for a visualisation of merge cases as a handy reference) Of course userfaultfd might be the offender here and might be relying on no merge case arising but passing dodgy parameters. [1]:https://ljs.io/merge_cases.png > > | 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.