From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Randy Dunlap <rdunlap@infradead.org>,
Peter Zijlstra <peterz@infradead.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-kernel@vger.kernel.org, aryabinin@virtuozzo.com,
dvyukov@google.com
Subject: Re: [PATCH] mm/uaccess: Use 'unsigned long' to placate UBSAN warnings, again
Date: Wed, 13 Jan 2021 17:27:04 -0600 [thread overview]
Message-ID: <20210113232704.66hqq4o5oes4up76@treble> (raw)
In-Reply-To: <202101071306.5A39AAC3A7@keescook>
On Thu, Jan 07, 2021 at 01:07:21PM -0800, Kees Cook wrote:
> On Wed, Jan 06, 2021 at 04:06:57PM -0800, Randy Dunlap wrote:
> > On 1/6/21 3:37 PM, Kees Cook wrote:
> > > On Mon, Jan 04, 2021 at 04:13:17PM +0100, Peter Zijlstra wrote:
> > >> On Tue, Dec 22, 2020 at 11:04:54PM -0600, Josh Poimboeuf wrote:
> > >>> GCC 7 has a known bug where UBSAN ignores '-fwrapv' and generates false
> > >>> signed-overflow-UB warnings. The type mismatch between 'i' and
> > >>> 'nr_segs' in copy_compat_iovec_from_user() is causing such a warning,
> > >>> which also happens to violate uaccess rules:
> > >>>
> > >>> lib/iov_iter.o: warning: objtool: iovec_from_user()+0x22d: call to __ubsan_handle_add_overflow() with UACCESS enabled
> > >>>
> > >>> Fix it by making the variable types match.
> > >>>
> > >>> This is similar to a previous commit:
> > >>>
> > >>> 29da93fea3ea ("mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions")
> > >>
> > >> Maybe it's time we make UBSAN builds depend on GCC-8+ ?
> > >
> > > I would be totally fine with that. The only thing I can think of that
> > > might care is syzbot. Dmitry, does syzbot use anything older than gcc 8?
> >
> > I use UBSAN successfully with GCC 7.5.0.
> > However, I can revert whatever future patch someone adds for this...
>
> Peter, which GCC version specifically are you seeing this on? (i.e. can
> I just make in 7.5+ instead of 8+ to make Randy's life easier?)
I don't think that would help, we saw this bug on GCC 7.5.
--
Josh
next prev parent reply other threads:[~2021-01-14 1:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-23 5:04 Josh Poimboeuf
2020-12-23 7:18 ` Randy Dunlap
2021-01-07 10:06 ` David Laight
2021-01-04 15:13 ` Peter Zijlstra
2021-01-06 23:37 ` Kees Cook
2021-01-07 0:06 ` Randy Dunlap
2021-01-07 21:07 ` Kees Cook
2021-01-13 23:27 ` Josh Poimboeuf [this message]
2021-01-07 10:51 ` Dmitry Vyukov
2021-01-14 10:59 ` [PATCH] ubsan: Require GCC-8+ or Clang to use UBSAN Peter Zijlstra
2021-01-14 11:09 ` Andrey Ryabinin
2021-01-18 17:53 ` Josh Poimboeuf
2021-02-09 18:24 ` Josh Poimboeuf
2021-02-09 23:17 ` Andrey Rybainin
2021-02-10 0:21 ` Kees Cook
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