linux-kernel - Re: [PATCH 0/9] mm: Hardened usercopy

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Message-ID: <20160708182344.GC4429@gmail.com>
Date:	Fri, 8 Jul 2016 20:23:44 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Kees Cook <keescook@...omium.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	the arch/x86 maintainers <x86@...nel.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	Mathias Krause <minipli@...glemail.com>,
	Jan Kara <jack@...e.cz>, Vitaly Wool <vitalywool@...il.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Laura Abbott <labbott@...oraproject.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	sparclinux@...r.kernel.org,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 0/9] mm: Hardened usercopy


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Fri, Jul 8, 2016 at 1:46 AM, Ingo Molnar <mingo@...nel.org> wrote:
> >
> > Could you please try to find some syscall workload that does many small user
> > copies and thus excercises this code path aggressively?
> 
> Any stat()-heavy path will hit cp_new_stat() very heavily. Think the
> usual kind of "traverse the whole tree looking for something". "git
> diff" will do it, just checking that everything is up-to-date.
> 
> That said, other things tend to dominate.

So I think a cached 'find /usr >/dev/null' might be a good one as well:

 triton:~/tip> strace -c find /usr >/dev/null
 % time     seconds  usecs/call     calls    errors syscall
 ------ ----------- ----------- --------- --------- ----------------
  47.09    0.006518           0    254697           newfstatat
  26.20    0.003627           0    254795           getdents
  14.45    0.002000           0   1147411           fcntl
   7.33    0.001014           0    509811           close
   3.28    0.000454           0    128220         1 openat
   1.52    0.000210           0    128230           fstat
   0.27    0.000016           0     12810           write
   0.00    0.000000           0        10           read

 triton:~/tip> perf stat --repeat 3 -e cycles:u,cycles:k,cycles find /usr >/dev/null

 Performance counter stats for 'find /usr' (3 runs):

     1,594,437,143      cycles:u                                                      ( +-  2.76% )
     2,570,544,009      cycles:k                                                      ( +-  2.50% )
     4,164,981,152      cycles                                                        ( +-  2.59% )

       0.929883686 seconds time elapsed                                          ( +-  2.57% )

... and it's dominated by kernel overhead, with a fair amount of memcpy overhead 
as well:

   1.22%  find     [kernel.kallsyms]   [k] copy_user_enhanced_fast_string                                                                                                            

But maybe there are simple shell commands that are even more user-memcpy intense? 

Thanks,

	Ingo