linux-kernel - Re: [PATCH -next] RFC: apparmor: Optimize retrieving current task secid

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Date:   Thu, 31 Aug 2023 19:54:26 -0700
From:   John Johansen <john.johansen@...onical.com>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        apparmor@...ts.ubuntu.com
Cc:     Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] RFC: apparmor: Optimize retrieving current task
 secid

On 8/31/23 19:45, Vinicius Costa Gomes wrote:
> John Johansen <john.johansen@...onical.com> writes:
> 
>> On 8/31/23 16:22, Vinicius Costa Gomes wrote:
>>> When running will-it-scale[1] open2_process testcase, in a system with a
>>> large number of cores, a bottleneck in retrieving the current task
>>> secid was detected:
>>>
>>> 27.73% ima_file_check;do_open (inlined);path_openat;do_filp_open;do_sys_openat2;__x64_sys_openat;do_syscall_x64 (inlined);do_syscall_64;entry_SYSCALL_64_after_hwframe (inlined);__libc_open64 (inlined)
>>>       27.72%     0.01%  [kernel.vmlinux]      [k] security_current_getsecid_subj             -      -
>>> 27.71% security_current_getsecid_subj;ima_file_check;do_open (inlined);path_openat;do_filp_open;do_sys_openat2;__x64_sys_openat;do_syscall_x64 (inlined);do_syscall_64;entry_SYSCALL_64_after_hwframe (inlined);__libc_open64 (inlined)
>>>       27.71%    27.68%  [kernel.vmlinux]      [k] apparmor_current_getsecid_subj             -      -
>>> 19.94% __refcount_add (inlined);__refcount_inc (inlined);refcount_inc (inlined);kref_get (inlined);aa_get_label (inlined);aa_get_label (inlined);aa_get_current_label (inlined);apparmor_current_getsecid_subj;security_current_getsecid_subj;ima_file_check;do_open (inlined);path_openat;do_filp_open;do_sys_openat2;__x64_sys_openat;do_syscall_x64 (inlined);do_syscall_64;entry_SYSCALL_64_after_hwframe (inlined);__libc_open64 (inlined)
>>> 7.72% __refcount_sub_and_test (inlined);__refcount_dec_and_test (inlined);refcount_dec_and_test (inlined);kref_put (inlined);aa_put_label (inlined);aa_put_label (inlined);apparmor_current_getsecid_subj;security_current_getsecid_subj;ima_file_check;do_open (inlined);path_openat;do_filp_open;do_sys_openat2;__x64_sys_openat;do_syscall_x64 (inlined);do_syscall_64;entry_SYSCALL_64_after_hwframe (inlined);__libc_open64 (inlined)
>>>
>>> A large amount of time was spent in the refcount.
>>>
>>> The most common case is that the current task label is available, and
>>> no need to take references for that one. That is exactly what the
>>> critical section helpers do, make use of them.
>>>
>>> New perf output:
>>>
>>> 39.12% vfs_open;path_openat;do_filp_open;do_sys_openat2;__x64_sys_openat;do_syscall_64;entry_SYSCALL_64_after_hwframe;__libc_open64 (inlined)
>>>       39.07%     0.13%  [kernel.vmlinux]          [k] do_dentry_open                                                               -      -
>>> 39.05% do_dentry_open;vfs_open;path_openat;do_filp_open;do_sys_openat2;__x64_sys_openat;do_syscall_64;entry_SYSCALL_64_after_hwframe;__libc_open64 (inlined)
>>>       38.71%     0.01%  [kernel.vmlinux]          [k] security_file_open                                                           -      -
>>> 38.70% security_file_open;do_dentry_open;vfs_open;path_openat;do_filp_open;do_sys_openat2;__x64_sys_openat;do_syscall_64;entry_SYSCALL_64_after_hwframe;__libc_open64 (inlined)
>>>       38.65%    38.60%  [kernel.vmlinux]          [k] apparmor_file_open                                                           -      -
>>> 38.65% apparmor_file_open;security_file_open;do_dentry_open;vfs_open;path_openat;do_filp_open;do_sys_openat2;__x64_sys_openat;do_syscall_64;entry_SYSCALL_64_after_hwframe;__libc_open64 (inlined)
>>>
>>> The result is a throughput improvement of around 20% across the board
>>> on the open2 testcase. On more realistic workloads the impact should
>>> be much less.
>>> hrmmm, interesting. its a nice improvement
>>
>>> [1] https://github.com/antonblanchard/will-it-scale
>>>
>>> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
>>
>> Acked-by: John Johansen <john.johansen@...onical.com>
>>
>> do you want me to pull this into apparmor-next or do you have another
>> tree in mind
>>
> 
> -next is fine.
> 
>>> ---
>>> Sending as RFC because I am not sure there's anything I am missing. My
>>> read of the code tells me it should be fine.
>>
>> it is
>>
> 
> Great. Do you want me to send a non-RFC version?
>
you can if you want but there is no need, I can do that small edit
  
>>>
>>>    security/apparmor/lsm.c | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
>>> index 108eccc5ada5..98e65c44ddd5 100644
>>> --- a/security/apparmor/lsm.c
>>> +++ b/security/apparmor/lsm.c
>>> @@ -766,9 +766,9 @@ static void apparmor_bprm_committed_creds(struct linux_binprm *bprm)
>>>    
>>>    static void apparmor_current_getsecid_subj(u32 *secid)
>>>    {
>>> -	struct aa_label *label = aa_get_current_label();
>>> +	struct aa_label *label = __begin_current_label_crit_section();
>>>    	*secid = label->secid;
>>> -	aa_put_label(label);
>>> +	__end_current_label_crit_section(label);
>>>    }
>>>    
>>>    static void apparmor_task_getsecid_obj(struct task_struct *p, u32 *secid)
>>
> 
> Cheers,