From: Andi Kleen <andi@firstfloor.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Andi Kleen <andi@firstfloor.org>,
dave@sr71.net, linux-kernel@vger.kernel.org, eranian@google.com,
x86@kernel.org, torvalds@linux-foundation.org,
Vitaly Mayatskikh <v.mayatskih@gmail.com>
Subject: Re: [PATCH 2/2] x86: Only do a single page fault for copy_from_user_nmi
Date: Sat, 4 Oct 2014 01:25:36 +0200 [thread overview]
Message-ID: <20141003232536.GG12538@two.firstfloor.org> (raw)
In-Reply-To: <20141003045359.GA24281@gmail.com>
> There are cleaner ways to solve this problem - PeterZ offered
> one, but there are other options as well, such as:
>
> - removing exact-bytes semantics explicitly from almost all
> cases and offering a separate (and more expensive, in the
> faulting case) memcpy variant for write() and other code that
> absolutely must know the number of copied bytes.
That would be a full tree audit of thousands of calls.
And any mistake would be a security hole.
> - or adding a special no-bytes-copied memcpy variant that the
> NMI code could use.
That's the duplicated copy path I mentioned. If people really want that
I can implement it, although I personally think it's ugly and bloated
over engineering for this case.
> It might be more work for you, but it gives us a cleaner and more
> maintainable kernel. The problem is that you should know this
> general principle already, instead you are wasting maintainer
> bandwidth via arguing in favor of ugly hacks again and again...
The duplicated path is unlikely to be more maintainable
than the simple and obvious check.
-Andi
prev parent reply other threads:[~2014-10-03 23:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-26 23:31 Optimize backtrace code for perf PMI handler Andi Kleen
2014-09-26 23:31 ` [PATCH 1/2] Use faster check for modules in backtrace on 64bit Andi Kleen
2014-09-29 11:42 ` Peter Zijlstra
2014-09-29 15:21 ` Andi Kleen
2014-09-29 20:30 ` Andi Kleen
2014-09-30 8:58 ` Peter Zijlstra
2014-09-30 20:10 ` Andi Kleen
2014-10-02 10:57 ` Peter Zijlstra
2014-10-03 23:20 ` Andi Kleen
2014-09-26 23:31 ` [PATCH 2/2] x86: Only do a single page fault for copy_from_user_nmi Andi Kleen
2014-09-29 11:56 ` Peter Zijlstra
2014-09-29 15:26 ` Andi Kleen
2014-10-03 4:53 ` Ingo Molnar
2014-10-03 23:25 ` Andi Kleen [this message]
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