linux-kernel - Re: [PATCH 3/3] audit: unify audit_filter_{uring(),inode

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Date:   Thu, 29 Sep 2022 13:23:55 -0700
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Ankur Arora <ankur.a.arora@...cle.com>, linux-audit@...hat.com,
        eparis@...hat.com, linux-kernel@...r.kernel.org,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH 3/3] audit: unify
 audit_filter_{uring(),inode_name(),syscall()}


Paul Moore <paul@...l-moore.com> writes:

> On Tue, Sep 27, 2022 at 7:00 PM Ankur Arora <ankur.a.arora@...cle.com> wrote:
>>
>> audit_filter_uring(), audit_filter_inode_name() are substantially similar
>> to audit_filter_syscall(). Move the core logic to __audit_filter() which
>> can be parametrized for all three.
>>
>> On a Skylakex system, getpid() latency (all results aggregated
>> across 12 boot cycles):
>>
>>          Min     Mean    Median   Max      pstdev
>>          (ns)    (ns)    (ns)     (ns)
>>
>>  -    173.11   182.51  179.65  202.09     (+- 4.34%)
>>  +    162.11   175.26  173.71  190.56     (+- 4.33%)
>>
>> Performance counter stats for 'bin/getpid' (3 runs) go from:
>>     cycles               706.13  (  +-  4.13% )
>>     instructions        1654.70  (  +-   .06% )
>>     IPC                    2.35  (  +-  4.25% )
>>     branches             430.99  (  +-   .06% )
>>     branch-misses          0.50  (  +-  2.00% )
>>     L1-dcache-loads      440.02  (  +-   .07% )
>>     L1-dcache-load-misses  5.22  (  +- 82.75% )
>>
>>  to:
>>     cycles               678.79  (  +-  4.22% )
>>     instructions        1657.79  (  +-   .05% )
>>     IPC                    2.45  (  +-  4.08% )
>>     branches             432.00  (  +-   .05% )
>>     branch-misses          0.38  (  +- 23.68% )
>>     L1-dcache-loads      444.96  (  +-   .03% )
>>     L1-dcache-load-misses  5.13  (  +- 73.09% )
>>
>> (Both aggregated over 12 boot cycles.)
>>
>> Unclear if the improvement is just run-to-run variation or because of
>> a slightly denser loop (the list parameter in the list_for_each_entry_rcu()
>> exit check now comes from a register rather than a constant as before.)
>>
>> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
>> ---
>>  kernel/auditsc.c | 86 +++++++++++++++++++++++++-----------------------
>>  1 file changed, 44 insertions(+), 42 deletions(-)
>>
>> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
>> index bf26f47b5226..dd89a52988b0 100644
>> --- a/kernel/auditsc.c
>> +++ b/kernel/auditsc.c
>> @@ -805,6 +805,41 @@ static bool audit_in_mask(const struct audit_krule *rule, unsigned long val)
>>         return rule->mask[word] & bit;
>>  }
>>
>> +/**
>> + * __audit_filter - common filter
>> + *
>
> Please remove the vertical whitespace between the function description
> line and the parameter descriptions.
>
> I'd also suggest renaming this function to "__audit_filter_op(...)"
> since we have a few audit filtering functions and a generic
> "__audit_filter()" function with no qualification in the name seems
> just a bit too generic to not be misleading ... at least I think so.
>
> I also might try to be just a bit more descriptive in the text above,
> for example:
>
> "__audit_filter_op - filter helper function for operations (syscall/uring/etc.)"
>
>> + * @tsk: associated task
>> + * @ctx: audit context
>> + * @list: audit filter list
>> + * @op: current syscall/uring_op
>> + * @name: name to be filtered (used by audit_filter_inode_name)
>
> I would change this to "@name: audit_name to use in filtering (can be
> NULL)" and leave it at that.
>
>> + *
>> + * return: 1 if we hit a filter, 0 if we don't
>
> The function header block comment description should be in regular
> English sentences.  Perhaps something like this:
>
> "Run the audit filters specified in @list against @tsk using @ctx,
> @op, and @name as necessary; the caller is responsible for ensuring
> that the call is made while the RCU read lock is held.  The @name
> parameter can be NULL, but all others must be specified.  Returns
> 1/true if the filter finds a match, 0/false if none are found."
>
>> + */
>> +static int __audit_filter(struct task_struct *tsk,
>> +                          struct audit_context *ctx,
>> +                          struct list_head *list,
>> +                          unsigned long op,
>> +                          struct audit_names *name)
>> +{
>> +       struct audit_entry *e;
>> +       enum audit_state state;
>> +
>> +       rcu_read_lock();
>
> I would move the RCU locking to the callers since not every caller requires it.
>
>> +       list_for_each_entry_rcu(e, list, list) {
>> +               if (unlikely(audit_in_mask(&e->rule, op))) {
>
> As discussed in patch 2/3, please remove the unlikely() call.

I'll pull it out of this patch.

And thanks for the comments. Will address and send out a v2.


Ankur

>
>> +                       if (audit_filter_rules(tsk, &e->rule, ctx, name,
>> +                                              &state, false)) {
>> +                               rcu_read_unlock();
>> +                               ctx->current_state = state;
>> +                               return 1;
>>  +                       }
>> +               }
>> +       }
>> +       rcu_read_unlock();
>> +       return 0;
>> +}
>> +