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]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20141003232536.GG12538@two.firstfloor.org \
--to=andi@firstfloor.org \
--cc=ak@linux.intel.com \
--cc=dave@sr71.net \
--cc=eranian@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=torvalds@linux-foundation.org \
--cc=v.mayatskih@gmail.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.