From: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Kees Cook <keescook@chromium.org>
Cc: Justin Stitt <justinstitt@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
llvm@lists.linux.dev
Subject: Re: [RFC] Mitigating unexpected arithmetic overflow
Date: Fri, 17 May 2024 09:45:20 +0200 [thread overview]
Message-ID: <99da3934-2c44-4a1f-832f-3f182ddadefa@huaweicloud.com> (raw)
In-Reply-To: <CAHk-=wjeiGb1UxCy6Q8aif50C=wWDX9Pgp+WbZYrO72+B1f_QA@mail.gmail.com>
Am 5/8/2024 um 10:07 PM schrieb Linus Torvalds:
> And no, the answer is ABSOLUTELY NOT to add cognitive load on kernel
> developers by adding yet more random helper types and/or functions.
Just to show an option without "more types and helper functions", one
could also instead add a coverage requirement:
Every arithmetic operation should either:
- have a test case where the wrap around happens, or
- have a static analyser say that overflow can not happen, or
- have a static analyser say that overflow is fine (e.g., your a+b < a case)
Then the answer to safe wrap situations isn't to make the kernel code
less readable, but to have a component-level test that shows that the
behavior on overflow (in at least one case :)) ) is what the developer
expected.
For static analysis to prove that overflow can not happen, one sometimes
would need to add BUG_ON() assertions to let the analyser know the
assumptions on surrounding code, which has its own benefits.
static inline u32 __item_offset(u32 val)
{
BUG_ON(val > INT_MAX / ITEM_SIZE_PER_UNIT);
return val * ITEM_SIZE_PER_UNIT;
}
Obviously, the effort involved is still high. Maybe if someone as a pet
project proves first that something in this direction is actually worth
the effort (by uncovering a heap of bugs), one could offer this kind of
check as an opt-in.
Best wishes,
jonas
next prev parent reply other threads:[~2024-05-17 7:45 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-07 23:27 [RFC] Mitigating unexpected arithmetic overflow Kees Cook
2024-05-08 12:22 ` David Laight
2024-05-08 23:43 ` Kees Cook
2024-05-08 17:52 ` Linus Torvalds
2024-05-08 19:44 ` Kees Cook
2024-05-08 20:07 ` Linus Torvalds
2024-05-08 22:54 ` Kees Cook
2024-05-08 23:47 ` Linus Torvalds
2024-05-09 0:06 ` Linus Torvalds
2024-05-09 0:23 ` Linus Torvalds
2024-05-09 6:11 ` Kees Cook
2024-05-09 14:08 ` Theodore Ts'o
2024-05-09 15:38 ` Linus Torvalds
2024-05-09 17:54 ` Al Viro
2024-05-09 18:08 ` Linus Torvalds
2024-05-09 18:39 ` Linus Torvalds
2024-05-09 18:48 ` Al Viro
2024-05-09 19:15 ` Linus Torvalds
2024-05-09 19:28 ` Al Viro
2024-05-09 21:06 ` David Laight
2024-05-18 5:11 ` Matthew Wilcox
2024-05-09 21:23 ` David Laight
2024-05-12 8:03 ` Martin Uecker
2024-05-12 16:09 ` Linus Torvalds
2024-05-12 19:29 ` Martin Uecker
2024-05-13 18:34 ` Kees Cook
2024-05-15 7:36 ` Peter Zijlstra
2024-05-15 17:12 ` Justin Stitt
2024-05-16 7:45 ` Peter Zijlstra
2024-05-16 13:30 ` Kees Cook
2024-05-16 14:09 ` Peter Zijlstra
2024-05-16 19:48 ` Justin Stitt
2024-05-16 20:07 ` Kees Cook
2024-05-16 20:51 ` Theodore Ts'o
2024-05-17 21:15 ` Kees Cook
2024-05-18 2:51 ` Theodore Ts'o
2024-05-17 22:04 ` Fangrui Song
2024-05-18 13:08 ` David Laight
2024-05-15 7:57 ` Peter Zijlstra
2024-05-17 7:45 ` Jonas Oberhauser [this message]
2024-05-11 16:19 ` Dan Carpenter
2024-05-13 19:43 ` Kees Cook
2024-05-14 8:45 ` Dan Carpenter
2024-05-18 15:39 ` David Laight
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