Fw:Re:[RFC,v1,1/1] audit: speed up syscall rule match while exiting syscall

[yang.yang29 at zte.com.cn]

Performance measurements:
1.Environment
CPU: Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz
Linux kernel version: 5.11-rc3
Audit version: 2.8.4

2.Result
2.1 Syscall invocations
Test method: 
    Run command "top" with no-load.
    Add rule likes "auditctl -a always,exit -F arch=b64 -S chmod -F auid=[number]" which doesn't hit audit.
    User command "perf record -Rg -t [top's pid] sleep 900" to get audit_filter_syscall()'s execute time ratio.

audit_filter_syscall() ratio with 100 rules:
    before this patch: 15.29%.
    after this patch: 0.88%, reduce 14.41%.
audit_filter_syscall() ratio with CIS[1] rules:
    before this patch: 2.25%.
    after this patch: 1.93%%, reduce 0.32%.
audit_filter_syscall() ratio with 10 rules:
    before this patch: 0.94%.
    after this patch: 1.02%, increase 0.08%.
audit_filter_syscall() ratio with 1 rule:
    before this patch: 0.20%.
    after this patch: 0.88%, increase 0.68%.

Analyse:
    With 1 rule, after this patch performance is worse, because mutex_lock()/mutex_unlock(). But user just add one rule seems unusual.
    With more rule, after this patch performance is improved.Typical likes CIS benchmark.

2.2 Rule change
Test method: 
    Use ktime_get_real_ts64() before and after audit_add_rule()/audit_del_rule() to calculate time.
     Add/delete rule by command "auditctl". Each test 10times and get average.

audit_add_rule() time:
    before this patch: 3120ns.
    after this patch: 7783ns, increase 149%.
audit_del_rule() time:
    before this patch: 3510ns.
    after this patch: 8519ns, increase 143%.

Analyse:
    After this patch, rule change time obviously increase. But rule change may not happen very often.

[1] CIS is a Linux Benchmarks for security purpose.
https://www.cisecurity.org/benchmark/distribution_independent_linux/

------------------Original Mail------------------
Sender: PaulMoore
To: yang yang10192021;
CC: Eric Paris;linux-audit at redhat.com;linux-kernel at vger.kernel.org;
Date: 2021/01/13 21:48
Subject: Re:[RFC,v1,1/1] audit: speed up syscall rule match while exiting syscall
On Wed, Jan 13, 2021 at 7:39 AM <yang.yang29 at zte.com.cn> wrote:
> From 82ebcf43481be21ee3e32ec1749b42f651737880 Mon Sep 17 00:00:00 2001
> From: Yang Yang <yang.yang29 at zte.com.cn>
> Date: Wed, 13 Jan 2021 20:18:04 +0800
> Subject: [PATCH] [RFC,v1,1/1] speed up syscall rule match while exiting syscall
>  If user add any syscall rule, in all syscalls, audit_filter_syscall()
>  traverses struct list_head audit_filter_list to find out whether current
>  syscall match one rule. This takes o(n), which is not necessary, specially
>  for user who add a very few syscall rules. On the other hand, user may not
>  much care about rule add/delete speed. So do o(n) calculate at rule changing,
>  and ease the burden of audit_filter_syscall().
>
>  Define audit_syscall[NR_syscalls], every element stands for one syscall.
>  audit_filter_syscall() checks audit_syscall[NR_syscalls].
>  audit_syscall[n] == 0 indicates no rule audit syscall n, do a quick exit.
>  audit_syscall[n] > 0 indicates at least one rule audit syscall n.
>  audit_syscall[n] update when syscall rule changes.
>
> Signed-off-by: Yang Yang <yang.yang29 at zte.com.cn>
> ---
>  include/linux/audit.h |  2 ++
>  kernel/audit.c        |  2 ++
>  kernel/auditfilter.c  | 16 ++++++++++++++++
>  kernel/auditsc.c      |  9 ++++++++-
>  4 files changed, 28 insertions(+), 1 deletion(-)

Before we go too far into a review of this patch, please provide some
performance measurements using a variety of rule counts, both common
and extreme, so that we can better judge the benefits of this patch.
The measurements should include both the rule add/delete time deltas
as well as the impact on the syscall invocations.  If non-obvious,
please also include how you performed the measurements and captured
the data.

These are good things to include in the commit description when
submitting patches focused on improving performance.

--
paul moore
www.paul-moore.com