From: David Hildenbrand <david@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
stable@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Peter Xu <peterx@redhat.com>, Hugh Dickins <hughd@google.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Vlastimil Babka <vbabka@suse.cz>,
John Hubbard <jhubbard@nvidia.com>,
Jason Gunthorpe <jgg@nvidia.com>
Subject: Re: [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW
Date: Tue, 9 Aug 2022 20:45:33 +0200 [thread overview]
Message-ID: <1a48d71d-41ee-bf39-80d2-0102f4fe9ccb@redhat.com> (raw)
In-Reply-To: <CAHk-=wiEAH+ojSpAgx_Ep=NKPWHU8AdO3V56BXcCsU97oYJ1EA@mail.gmail.com>
On 09.08.22 20:27, Linus Torvalds wrote:
> I'm still reading through this, but
>
> STOP DOING THIS
>
> On Mon, Aug 8, 2022 at 12:32 AM David Hildenbrand <david@redhat.com> wrote:
>>
>> + VM_BUG_ON(!is_cow_mapping(vma->vm_flags));
>
> Using BUG_ON() for debugging is simply not ok.
>
> And saying "but it's just a VM_BUG_ON()" does not change *anything*.
> At least Fedora enables that unconditionally for normal people, it is
> not some kind of "only VM people do this".
>
> Really. BUG_ON() IS NOT FOR DEBUGGING.
I totally agree with BUG_ON ... but if I get talked to in all-caps on a
Thursday evening and feel like I just touched the forbidden fruit, I
have to ask for details about VM_BUG_ON nowadays.
VM_BUG_ON is only active with CONFIG_DEBUG_VM. ... which indicated some
kind of debugging at least to me. I *know* that Fedora enables it and I
*know* that this will make Fedora crash.
I know why Fedora enables this debug option, but it somewhat destorys
the whole purpose of VM_BUG_ON kind of nowadays?
For this case, this condition will never trigger and I consider it much
more a hint to the reader that we can rest assured that this condition
holds. And on production systems, it will get optimized out.
Should we forbid any new usage of VM_BUG_ON just like we mostly do with
BUG_ON?
>
> Stop it. Now.
>
> If you have a condition that must not happen, you either write that
> condition into the code, or - if you are convinced it cannot happen -
> you make it a WARN_ON_ONCE() so that people can report it to you.
I can just turn that into a WARN_ON_ONCE() or even a VM_WARN_ON_ONCE().
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2022-08-09 18:45 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-08 7:32 [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW David Hildenbrand
2022-08-08 16:02 ` David Hildenbrand
2022-08-09 18:27 ` Linus Torvalds
2022-08-09 18:45 ` David Hildenbrand [this message]
2022-08-09 18:59 ` Linus Torvalds
2022-08-09 19:07 ` Jason Gunthorpe
2022-08-09 19:21 ` Linus Torvalds
2022-08-09 21:16 ` David Laight
2022-08-11 7:13 ` [PATCH] sched/all: Change BUG_ON() instances to WARN_ON() Ingo Molnar
2022-08-11 20:43 ` Linus Torvalds
2022-08-11 21:28 ` Matthew Wilcox
2022-08-11 23:22 ` Jason Gunthorpe
2022-08-14 1:10 ` John Hubbard
2022-08-12 9:29 ` [PATCH v2] sched/all: Change all BUG_ON() instances in the scheduler to WARN_ON_ONCE() Ingo Molnar
[not found] ` <20220815144143.zjsiamw5y22bvgki@suse.de>
2022-08-15 22:12 ` John Hubbard
2022-08-21 11:28 ` Ingo Molnar
2022-08-09 18:40 ` [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW Linus Torvalds
2022-08-09 18:48 ` Jason Gunthorpe
2022-08-09 18:53 ` David Hildenbrand
2022-08-09 19:07 ` Linus Torvalds
2022-08-09 19:20 ` David Hildenbrand
2022-08-09 18:48 ` Linus Torvalds
2022-08-09 19:09 ` David Hildenbrand
2022-08-09 20:00 ` Linus Torvalds
2022-08-09 20:06 ` David Hildenbrand
2022-08-09 20:07 ` David Hildenbrand
2022-08-09 20:14 ` Linus Torvalds
2022-08-09 20:20 ` David Hildenbrand
2022-08-09 20:30 ` Linus Torvalds
2022-08-09 20:38 ` Linus Torvalds
2022-08-09 20:42 ` David Hildenbrand
2022-08-09 20:20 ` Linus Torvalds
2022-08-09 20:23 ` David Hildenbrand
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