[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Mon, 10 Dec 2018 00:32:21 +0200
From: Igor Stoppa <igor.stoppa@...il.com>
To: Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>
Cc: linux-arch <linux-arch@...r.kernel.org>,
linux-s390 <linux-s390@...r.kernel.org>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Kees Cook <keescook@...omium.org>, Matthew Wilcox <willy@...radead.org>,
Igor Stoppa <igor.stoppa@...wei.com>, Nadav Amit <nadav.amit@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
linux-integrity <linux-integrity@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] __wr_after_init: write rare for static allocation
On 06/12/2018 11:44, Peter Zijlstra wrote:
> On Wed, Dec 05, 2018 at 03:13:56PM -0800, Andy Lutomirski wrote:
>
>>> + if (op == WR_MEMCPY)
>>> + memcpy((void *)wr_poking_addr, (void *)src, len);
>>> + else if (op == WR_MEMSET)
>>> + memset((u8 *)wr_poking_addr, (u8)src, len);
>>> + else if (op == WR_RCU_ASSIGN_PTR)
>>> + /* generic version of rcu_assign_pointer */
>>> + smp_store_release((void **)wr_poking_addr,
>>> + RCU_INITIALIZER((void **)src));
>>> + kasan_enable_current();
>>
>> Hmm. I suspect this will explode quite badly on sane architectures
>> like s390. (In my book, despite how weird s390 is, it has a vastly
>> nicer model of "user" memory than any other architecture I know
>> of...). I think you should use copy_to_user(), etc, instead. I'm not
>> entirely sure what the best smp_store_release() replacement is.
>> Making this change may also mean you can get rid of the
>> kasan_disable_current().
>
> If you make the MEMCPY one guarantee single-copy atomicity for native
> words then you're basically done.
>
> smp_store_release() can be implemented with:
>
> smp_mb();
> WRITE_ONCE();
>
> So if we make MEMCPY provide the WRITE_ONCE(), all we need is that
> barrier, which we can easily place at the call site and not overly
> complicate our interface with this.
Ok, so the 3rd case (WR_RCU_ASSIGN_PTR) could be handled outside of this
function.
But, since now memcpy() will be replaced by copy_to_user(), can I assume
that also copy_to_user() will be atomic, if the destination is properly
aligned? On x86_64 it seems yes, however it's not clear to me if this is
the outcome of an optimization or if I can expect it to be always true.
--
igor
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
