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From: Nick Desaulniers <ndesaulniers@google.com>
To: David.Laight@aculab.com
Cc: "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
	dhowells@redhat.com, Nathan Chancellor <natechancellor@gmail.com>,
	Eric Biggers <ebiggers@google.com>,
	zohar@linux.vnet.ibm.com, jmorris@namei.org, serge@hallyn.com,
	linux-integrity@vger.kernel.org, keyrings@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KEYS: trusted: fix -Wvarags warning
Date: Mon, 15 Oct 2018 14:53:49 -0700
Message-ID: <CAKwvOdmXVY1iA-VAs-Ns3qVVnMTeU6v4RqxoS2=SJcSeQ23_og@mail.gmail.com> (raw)
In-Reply-To: <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com>

On Mon, Oct 15, 2018 at 2:26 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: ndesaulniers@google.com
> > Sent: 11 October 2018 21:31
> ...
> > by swapping h2 and h3.
> >
> > security/keys/trusted.c:146:17: warning: passing an object that
> > undergoes default
> >       argument promotion to 'va_start' has undefined behavior [-Wvarargs]
> >         va_start(argp, h3);
> >                        ^
> > security/keys/trusted.c:126:37: note: parameter of type 'unsigned
> > char' is declared here
> > unsigned char *h2, unsigned char h3, ...)
> >                                ^
> > Specifically, it seems that both the C90 (4.8.1.1) and C11 (7.16.1.4)
> > standards explicitly call this out as undefined behavior:
>
> I guess that problems arise when all the arguments are stacked
> and va_start/va_arg use naive pointer manipulation.
> In that case &h3 might be 4n+3 aligned so va_arg() will access
> misaligned stack locations.
>
> I doubt any modern compilers (where va_start and va_arg are builtins)
> will get this 'wrong' even when all arguments are stacked.
>
> Seems clang is being over cautious.

Yes; did you have feedback on the Denis' proposed fix, or another?

>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)



-- 
Thanks,
~Nick Desaulniers

  parent reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-09 22:11 undefined behavior (-Wvarargs) in security/keys/trusted.c#TSS_authhmac() Nick Desaulniers
2018-10-11 16:02 ` Arnd Bergmann
2018-10-11 16:10   ` James Bottomley
2018-10-11 20:31     ` [PATCH] KEYS: trusted: fix -Wvarags warning ndesaulniers
2018-10-12  1:50       ` Nathan Chancellor
2018-10-12 16:55         ` Nick Desaulniers
2018-10-12 17:03           ` Nathan Chancellor
2018-10-12 12:29       ` Denis Kenzior
2018-10-12 15:05         ` James Bottomley
2018-10-12 15:13           ` Denis Kenzior
2018-10-12 15:22             ` James Bottomley
2018-10-12 15:44               ` Denis Kenzior
2018-10-12 15:46                 ` James Bottomley
2018-10-12 15:53                   ` Denis Kenzior
2018-10-12 16:01                     ` James Bottomley
2018-10-12 17:14                       ` Nick Desaulniers
2018-10-12 15:25             ` James Bottomley
2018-10-12 17:05             ` Nick Desaulniers
2018-10-12 17:17               ` Nick Desaulniers
2018-10-12 17:27               ` Denis Kenzior
2018-10-12 18:39                 ` Nick Desaulniers
2018-10-12 17:02         ` Nick Desaulniers
2018-10-12 17:15           ` Denis Kenzior
2018-10-15  9:26       ` David Laight
2018-10-15  9:26         ` David Laight
2018-10-15 21:53         ` Nick Desaulniers [this message]
2018-10-16  8:13           ` David Laight
2018-10-16  8:13             ` David Laight
2018-10-22 23:43             ` [PATCH v2] " ndesaulniers
2018-10-23  0:00               ` Nathan Chancellor
2018-10-24  8:36               ` Jarkko Sakkinen
2018-10-29 17:54                 ` Nick Desaulniers
2019-02-11 18:36                   ` Nick Desaulniers
2019-02-12 23:12                     ` Jarkko Sakkinen
2019-02-14 10:52                       ` Jarkko Sakkinen

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