From: David Laight <David.Laight@ACULAB.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-hardening@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"llvm@lists.linux.dev" <llvm@lists.linux.dev>
Subject: RE: [RFC] Mitigating unexpected arithmetic overflow
Date: Thu, 9 May 2024 21:23:29 +0000 [thread overview]
Message-ID: <f41cd250b90d4eb883ea5ff245718200@AcuMS.aculab.com> (raw)
In-Reply-To: <CAHk-=wgoE5EkH+sQwi4KhRhCZizUxwZAnC=+9RbZcw7g6016LQ@mail.gmail.com>
...
> I think that would be a completely different area that might be worth
> looking at: instrumenting implicit casts for "drops bits". I'm afraid
> that it's just *so* common than we might not be able to do that
> sanely.
Things like:
buf[0] = val;
buf[1] = val >>= 8;
buf[2] = val >>= 8;
buf[3] = val >>= 8;
for writing a value little-endian and potentially misaligned.
Really doesn't want any annotation.
I've also seen code like:
buf[0] = (unsigned char)(val & 0xff);
not only ugly by it got compiled to:
val &= 0xff // for the &
val &= 0xff // for the cast
byte write to memory.
Modern gcc doesn't do that, but...
There are some spurious casts that drop bits.
I found plenty of dubious min_t(u8/u16,...) examples.
(Well they are dubious, some are just a lot more dubious than others.)
The problem is that every one needs careful inspection just in case
the strange behaviour is required like min_t(u8, val - 1, lo_lim - 1)
which treats lo_lim of zero as 'not a limit' and I think was ok.
A slow, concerted effort to remove min_t() calls wouldn't be a bad thing.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2024-05-09 21:24 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 [this message]
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
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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