From: Andrey Rybainin <ryabinin.a.a@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-next@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Randy Dunlap <rdunlap@infradead.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Dmitry Vyukov <dvyukov@google.com>,
Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH] ubsan: remove overflow checks
Date: Wed, 10 Feb 2021 14:55:20 +0300 [thread overview]
Message-ID: <460f8e86-f602-d3ae-1287-0042c510a165@gmail.com> (raw)
In-Reply-To: <202102091617.8FD77890@keescook>
On 2/10/21 3:19 AM, Kees Cook wrote:
> On Wed, Feb 10, 2021 at 02:23:48AM +0300, Andrey Ryabinin wrote:
>> Since GCC 8.0 -fsanitize=signed-integer-overflow doesn't work with -fwrapv.
>> -fwrapv makes signed overflows defines and GCC essentially disables
>> ubsan checks. On GCC < 8.0 -fwrapv doesn't have influence on
>> -fsanitize=signed-integer-overflow setting, so it kinda works
>> but generates false-positves and violates uaccess rules:
>>
>> lib/iov_iter.o: warning: objtool: iovec_from_user()+0x22d: call to __ubsan_handle_add_overflow() with UACCESS enabled
>>
>> Disable signed overflow checks to avoid these problems.
>> Remove unsigned overflow checks as well.
>> Unsigned overflow appeared as side effect of the commit
>> cdf8a76fda4a ("ubsan: move cc-option tests into Kconfig"),
>> but it never worked (kernel doesn't boot). And unsigned overflows
>> are allowed by C standard, so it just pointless.
>>
>> Signed-off-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
>
> NAK, please don't remove the entire thing. I want this to work again
> with -fwrapv, and it's not entirely broken under Clang. But the feature
> shouldn't be removed from the kernel.
>
This is dead code. How exactly it's useful to keep it? You can always resurrect it later when you'll need it.
Clang has the same behavior as GCC > 8, signed-integer-overflow does nothing when compiled -fwrapv or -fno-strict-overflow
next prev parent reply other threads:[~2021-02-10 11:57 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-08 12:52 linux-next: Tree for Feb 8 Stephen Rothwell
2021-02-08 19:30 ` linux-next: Tree for Feb 8 (objtool: warnings: 5) Randy Dunlap
2021-02-08 21:21 ` Josh Poimboeuf
2021-02-08 21:39 ` Randy Dunlap
2021-02-09 22:59 ` Josh Poimboeuf
2021-02-10 0:16 ` Randy Dunlap
2021-02-09 8:06 ` Peter Zijlstra
2021-02-09 23:23 ` [PATCH] ubsan: remove overflow checks Andrey Ryabinin
2021-02-10 0:19 ` Kees Cook
2021-02-10 7:50 ` Peter Zijlstra
2021-02-10 11:55 ` Andrey Rybainin [this message]
2021-02-09 8:34 ` [PATCH] lockdep: Noinstr annotate warn_bogus_irq_restore() Peter Zijlstra
2021-02-09 13:24 ` Mark Rutland
2021-02-09 16:03 ` Peter Zijlstra
2021-02-09 16:13 ` Mark Rutland
2021-02-09 18:28 ` Randy Dunlap
2021-02-10 13:59 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-02-09 3:33 ` linux-next: Tree for Feb 8 (Warning at arch/x86/kernel/irq.c:390) Randy Dunlap
2021-02-09 10:17 ` Borislav Petkov
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