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

[John Johansen]

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 at intel.com>

Acked-by: John Johansen <john.johansen at canonical.com>

do you want me to pull this into apparmor-next or do you have another
tree in mind

> ---
> 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

> 
>   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)