On Fri, 27 Feb 2026 10:20:38 -0500 Steven Rostedt <[email protected]> wrote:
> On Fri, 27 Feb 2026 11:22:22 +0000 > Vincent Donnefort <[email protected]> wrote: > > > > Ah right, Syzkaller is using madvise(MADVISE_DOFORK) which resets > > > VM_DONTCOPY. > > > > As we are applying restrictive rules for this mapping, I believe setting > > VM_IO > > might be a better fix. > > Agreed. > Adding MM folks so we do this right. Dear MM folks, Here's the issue. When the ftrace ring buffer is memory mapped to user space, we do not want anything "special" done to it. One of those things we did not want done was to have it copied on fork. To do that, we added VM_DONTCOPY, but we didn't know that an madvise() could disable that. It looks like VM_IO will prevent that from happening. But looking at the various flags, I see there's a VM_SPECIAL. I'm wondering if that is what we should use? The effected code is here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/trace/ring_buffer.c#n7172 What's your thoughts? Thanks, -- Steve
