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From: David Laight <David.Laight@ACULAB.COM>
To: "'ndesaulniers@google.com'" <ndesaulniers@google.com>,
	"jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>,
	"dhowells@redhat.com" <dhowells@redhat.com>
Cc: "natechancellor@gmail.com" <natechancellor@gmail.com>,
	"ebiggers@google.com" <ebiggers@google.com>,
	Mimi Zohar <zohar@linux.vnet.ibm.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] KEYS: trusted: fix -Wvarags warning
Date: Mon, 15 Oct 2018 09:26:02 +0000
Message-ID: <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com> (raw)
Message-ID: <20181015092602.lI4hBvr-AVjCfM6TjoszcxHkJ3xKRBFKV0YjswEZv08@z> (raw)
In-Reply-To: <20181011203126.15338-1-ndesaulniers@google.com>

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.

	David

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

  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 [this message]
2018-10-15  9:26         ` David Laight
2018-10-15 21:53         ` Nick Desaulniers
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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