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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 22 Feb 2018 12:18:02 +0100
Message-ID: <CAK8P3a3a-2FAZ0hTGwnQpREn5qov5jhWC_HrR0Vbf8X=EywBSA@mail.gmail.com>
Subject: Re: [PATCH 00/31 v2] PTI support for x86_32
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Lorenzo Colitti <lorenzo@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Mark D Rustad <mrustad@gmail.com>,
        Adam Borowski <kilobyte@angband.pl>,
        Joerg Roedel <jroedel@suse.de>,
        Andy Lutomirski <luto@kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Brian Gerst <brgerst@gmail.com>,
        David Laight <David.Laight@aculab.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Eduardo Valentin <eduval@amazon.com>,
        Will Deacon <will.deacon@arm.com>,
        "Liguori, Anthony" <aliguori@amazon.com>,
        Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
        Hugh Dickins <hughd@google.com>,
        Kees Cook <keescook@google.com>,
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On Thu, Feb 22, 2018 at 12:10 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Wed, Feb 21, 2018 at 05:59:34PM +0100, Arnd Bergmann wrote:
>> On Wed, Feb 21, 2018 at 11:26 AM, Lorenzo Colitti <lorenzo@google.com> wrote:
>> > On Wed, Feb 14, 2018 at 5:54 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
>> >> > > IPSEC doesn't work with a 64bit kernel and 32bit userspace right now.
>> >> > >
>> >> > > Back in 2015 someone started to work on that, and properly marked that
>> >> > > the kernel could not handle this with commit 74005991b78a ("xfrm: Do not
>> >> > > parse 32bits compiled xfrm netlink msg on 64bits host")
>> >> > >
>> >> > > This is starting to be hit by some Android systems that are moving
>> >> > > (yeah, slowly) to 4.4 :(
>> >> >
>> >> > Does anybody have test-programs/harnesses for this?
>> >>
>> >> Lorenzo (now on the To: line), is the one that I think is looking into
>> >> this, and should have some sort of test for it.  Lorenzo?
>> >
>> > Sorry for the late reply here. The issue is that the xfrm uapi structs
>> > don't specify padding at the end, so they're a different size on
>> > 32-bit and 64-bit archs. This by itself would be fine, as the kernel
>> > could just ignore the (lack of) padding. But some of these structs
>> > contain others (e.g., xfrm_userspi_info contains xfrm_usersa_info),
>> > and in that case the whole layout after the contained struct is
>> > different.
>>
>> So this is x86 specific then and it already works correctly on all
>> other architectures (especially arm64 Android), right?
>
> Why is this an x86-specific issue?  I think people have noticed this
> with ARM systems given that the original bug report I saw was for an
> ARM Android-based system that had a 64bit kernel and 32bit userspace.

The patch Lorenzo linked to is only for x86, it addresses the fact that
the padding at the end of xfrm_usersa_info differs between 32-bit x86
and all other architectures because of the x86 specific quirk that u64
variables have 32-bit alignment.

xfrm_usersa_info should have the exact same layout on arm32, arm64
and x86_64.

      Arnd