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 [thread overview]
Message-ID: <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com> (raw)
In-Reply-To: <20181011203126.15338-1-ndesaulniers@google.com>
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WARNING: multiple messages have this Message-ID (diff)
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 [thread overview]
Message-ID: <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com> (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
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
WARNING: multiple messages have this Message-ID (diff)
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 [thread overview]
Message-ID: <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com> (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
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2018-10-15 9:26 UTC|newest]
Thread overview: 68+ 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
2018-10-09 22:11 ` Nick Desaulniers
2018-10-11 16:02 ` Arnd Bergmann
2018-10-11 16:02 ` Arnd Bergmann
2018-10-11 16:10 ` James Bottomley
2018-10-11 16:10 ` James Bottomley
2018-10-11 20:31 ` [PATCH] KEYS: trusted: fix -Wvarags warning ndesaulniers
2018-10-11 20:31 ` ndesaulniers
2018-10-12 1:50 ` Nathan Chancellor
2018-10-12 1:50 ` Nathan Chancellor
2018-10-12 16:55 ` Nick Desaulniers
2018-10-12 16:55 ` Nick Desaulniers
2018-10-12 17:03 ` Nathan Chancellor
2018-10-12 17:03 ` Nathan Chancellor
2018-10-12 12:29 ` Denis Kenzior
2018-10-12 12:29 ` Denis Kenzior
2018-10-12 15:05 ` James Bottomley
2018-10-12 15:05 ` James Bottomley
2018-10-12 15:13 ` Denis Kenzior
2018-10-12 15:13 ` Denis Kenzior
2018-10-12 15:22 ` James Bottomley
2018-10-12 15:22 ` James Bottomley
2018-10-12 15:44 ` Denis Kenzior
2018-10-12 15:44 ` Denis Kenzior
2018-10-12 15:46 ` James Bottomley
2018-10-12 15:46 ` James Bottomley
2018-10-12 15:53 ` Denis Kenzior
2018-10-12 15:53 ` Denis Kenzior
2018-10-12 16:01 ` James Bottomley
2018-10-12 16:01 ` James Bottomley
2018-10-12 17:14 ` Nick Desaulniers
2018-10-12 17:14 ` Nick Desaulniers
2018-10-12 15:25 ` James Bottomley
2018-10-12 15:25 ` James Bottomley
2018-10-12 17:05 ` Nick Desaulniers
2018-10-12 17:05 ` Nick Desaulniers
2018-10-12 17:17 ` Nick Desaulniers
2018-10-12 17:17 ` Nick Desaulniers
2018-10-12 17:27 ` Denis Kenzior
2018-10-12 17:27 ` Denis Kenzior
2018-10-12 18:39 ` Nick Desaulniers
2018-10-12 18:39 ` Nick Desaulniers
2018-10-12 17:02 ` Nick Desaulniers
2018-10-12 17:02 ` Nick Desaulniers
2018-10-12 17:15 ` Denis Kenzior
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 9:26 ` David Laight
2018-10-15 21:53 ` Nick Desaulniers
2018-10-15 21:53 ` Nick Desaulniers
2018-10-16 8:13 ` David Laight
2018-10-16 8:13 ` David Laight
2018-10-16 8:13 ` David Laight
2018-10-22 23:43 ` [PATCH v2] " ndesaulniers
2018-10-22 23:43 ` ndesaulniers
2018-10-23 0:00 ` Nathan Chancellor
2018-10-23 0:00 ` Nathan Chancellor
2018-10-24 8:36 ` Jarkko Sakkinen
2018-10-24 8:36 ` Jarkko Sakkinen
2018-10-29 17:54 ` Nick Desaulniers
2018-10-29 17:54 ` Nick Desaulniers
2019-02-11 18:36 ` Nick Desaulniers
2019-02-11 18:36 ` Nick Desaulniers
2019-02-12 23:12 ` Jarkko Sakkinen
2019-02-12 23:12 ` Jarkko Sakkinen
2019-02-14 10:52 ` Jarkko Sakkinen
2019-02-14 10:52 ` Jarkko Sakkinen
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