From: Stephen Rothwell <sfr@canb•auug.org.au>
To: Dave Hansen <dave@sr71•net>
Cc: linux-kernel@vger•kernel.org, dave.hansen@linux•intel.com,
akpm@linux-foundation•org, tglx@linutronix•de, mingo@elte•hu,
hpa@zytor•com, peterz@infradead•org, linux-next@vger•kernel.org,
deller@gmx•de
Subject: Re: [PATCH] [v2] x86, pkeys: fix siginfo ABI breakage from new field
Date: Tue, 1 Mar 2016 09:13:31 +1100 [thread overview]
Message-ID: <20160301091331.0ce9f1da@canb.auug.org.au> (raw)
In-Reply-To: <20160229194931.7600FB60@viggo.jf.intel.com>
Hi Dave,
On Mon, 29 Feb 2016 11:49:31 -0800 Dave Hansen <dave@sr71•net> wrote:
>
> This responds to the feedback from Ingo that we should be using
> explicitly-sized types.
Beat me to it by seconds :-)
> From: Dave Hansen <dave.hansen@linux•intel.com>
>
> Stephen Rothwell reported:
>
> http://lkml.kernel.org/r/20160226164406.065a1ffc@canb.auug.org.au
>
> that the Memory Protection Keys patches from the tip tree broke
> a build-time check on an ARM build because they changed the ABI
> of siginfo.
>
> A u64 was used for the protection key field in siginfo. When the
> containing union was aligned, this u64 unioned nicely with the
> two 'void *'s in _addr_bnd. But, on 32-bit, if the union was
> unaligned, the u64 might grow the size of the union, breaking the
> ABI for subsequent fields.
>
> To fix this, we replace the u64 with an 'unsigned long'. The long
> is guaranteed to union well with the pointers from _addr_bnd. It
> is also plenty large enough to store the 16-bit pkey we have today
> on x86. This also has the advantage that it allows existing 64-bit
> userspace to keep working without modification.
s/(unsigned )?long/__u32/g
and the last sentence no longer makes sense.
> I also shouldn't have been using a u64 in a userspace API to begin
> with.
>
> Fixes: cd0ea35ff551 ("signals, pkeys: Notify userspace about protection key faults")
> Signed-off-by: Dave Hansen <dave.hansen@linux•intel.com>
> Cc: Stephen Rothwell <sfr@canb•auug.org.au>
> Cc: Andrew Morton <akpm@linux-foundation•org>
> Cc: Thomas Gleixner <tglx@linutronix•de>
> Cc: Ingo Molnar <mingo@elte•hu>
> Cc: "H. Peter Anvin" <hpa@zytor•com>
> Cc: Peter Zijlstra <peterz@infradead•org>
> Cc: linux-next@vger•kernel.org
> Cc: linux-kernel@vger•kernel.org
> Cc: Helge Deller <deller@gmx•de>
Acked-by: Stehen Rothwell <sfr@canb•auug.org.au>
--
Cheers,
Stephen Rothwell
prev parent reply other threads:[~2016-02-29 22:13 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-29 19:49 [PATCH] [v2] x86, pkeys: fix siginfo ABI breakage from new field Dave Hansen
2016-02-29 22:13 ` Stephen Rothwell [this message]
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