linux-kernel - Re: [PATCH] seccomp: fix populating a0-a5 syscall args in 32-bit x86 BPF

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Date:	Mon, 14 Apr 2014 13:28:52 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	David Miller <davem@...emloft.net>
Cc:	dborkman@...hat.com, Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	ast@...mgrid.com, Eric Paris <eparis@...hat.com>,
	James Morris <james.l.morris@...cle.com>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] seccomp: fix populating a0-a5 syscall args in 32-bit x86 BPF

On Mon, Apr 14, 2014 at 1:24 PM, David Miller <davem@...emloft.net> wrote:
> From: Andy Lutomirski <luto@...capital.net>
> Date: Mon, 14 Apr 2014 13:13:45 -0700
>
>> I think this description is wrong.  (unsigned long *) &sd->args[1] is
>> the right location, at least on 32-bit little-endian architectures.
>
> It absolutely is not.

Huh?  It's a pointer to the right address, but the type is wrong.

The changelog says "on 32-bit x86 (or any other 32bit arch), it would
result in storing a0-a5 at wrong offsets in args[] member".  Unless
I'm mistaken, this is incorrect: a0-a5 are are the correct offsets,
but they are stored with the wrong type, so the other bits in there
are garbage.

>
> The thing is a u64, and we must respect that type in a completely
> portable way.
>
> Daniel's change is %100 correct, portable, and doesn't have any
> ugly ifdef crap.
>

I have no problem with the patch itself.  I'm suggesting that a better
changelog message would confuse other people reading the same patch
less.

--Andy
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