Re: [PATCH 00/31 v2] PTI support for x86_32

[Arnd Bergmann]

On Thu, Feb 22, 2018 at 12:10 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxx> wrote:
>> > On Wed, Feb 14, 2018 at 5:54 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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