Re: [PATCH 00/18] xfrm: Add compat layer

Dmitry Safonov
2018-07-28T16:26:55Z

On Fri, 2018-07-27 at 09:48 -0700, Nathan Harold wrote:
> We (Android) are very interested in removing the restriction for 32-
> bit userspace processes accessing xfrm netlink on 64-bit kernels.
> IPsec support is required to pass Android conformance tests, and any
> manufacturer wishing to ship 32-bit userspace with a recent kernel
> needs out-of-tree changes (removing the compat_task check) to do so.

Glad to hear - that justify my attempts more :)

> That said, it’s not difficult to work around alignment issues
> directly in userspace, so maybe we could just remove the check and
> make this the caller's responsibility? Here’s an example of the
> workaround currently in the Android tree:
> https://android.googlesource.com/platform/system/netd/+/refs/heads/ma
> ster/server/XfrmController.h#257

We've kinda same workarounds in our userspace..
But I don't think reverting the check makes much sense - it'll make
broken compat ABI in stone.
If you're fine with disgraceful hacks and just want to get rid of
additional non-mainstream patch - you can make 64-bit syscalls from 32-
bit task (hint: examples in x86 selftests).

> We could also employ a (relatively simple) solution such as the one
> above in the uapi XFRM header itself, though it would require a
> caller to declare the target kernel ABI at compile time. Maybe that’s
> not unthinkable for an uncommon case?

Well, I think, I'll rework my patches set according to critics and
separate compat xfrm layer. I've already a selftest to check that 32/64
bit xfrm works - so the most time-taking part is done.
So, if you'll wait a week or two - you may help me to justify acception
of mainstreaming those patches.

> On Fri, Jul 27, 2018 at 7:51 AM, Dmitry Safonov <dima@arista.com>
> wrote:
> > On Fri, 2018-07-27 at 16:19 +0200, Florian Westphal wrote:
> > > Dmitry Safonov <dima@arista.com> wrote:
> > > > 1. It will double copy netlink messages, making it O(n) instead
> > of
> > > > O(1), where n - is number of bind()s.. Probably we don't care
> > much.
> > >
> > > About those bind() patches, I don't understand why they are
> > needed.
> > >
> > > Why can't you just add the compat skb to the native skb when
> > doing
> > > the multicast call?
> > >
> > > skb_shinfo(skb)->frag_list = compat_skb;
> > > xfrm_nlmsg_multicast(net, skb, 0, ...
> >
> > Oh yeah, sorry, I think I misread the patch - will try to add
> > compat
> > skb in the multicast call.
> >

--
Thanks,
Dmitry