linux-kernel - Re: [PATCH 1/3] audit: cache ctx->major in audit_filter

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Message-ID: <CAHC9VhRZzU5-+65AFOK826rA0xo-nbgRK_pP05Q_zjvAQvLnRw@mail.gmail.com>
Date:   Wed, 28 Sep 2022 18:03:08 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-audit@...hat.com, eparis@...hat.com,
        linux-kernel@...r.kernel.org, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com
Subject: Re: [PATCH 1/3] audit: cache ctx->major in audit_filter_syscall()

On Tue, Sep 27, 2022 at 6:59 PM Ankur Arora <ankur.a.arora@...cle.com> wrote:
>
> ctx->major contains the current syscall number. This is, of course, a
> constant for the duration of the syscall. Unfortunately, GCC's alias
> analysis cannot prove that it is not modified via a pointer in the
> audit_filter_syscall() loop, and so always loads it from memory.
>
> ...
>
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> ---
>  kernel/auditsc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

This looks pretty trivial to me, but it's too late in the current -rc
cycle for this to be merged, I'll queue it up for after the upcoming
merge window closes.  Thanks.

> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 79a5da1bc5bb..533b087c3c02 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -843,13 +843,14 @@ static void audit_filter_syscall(struct task_struct *tsk,
>  {
>         struct audit_entry *e;
>         enum audit_state state;
> +       unsigned long major = ctx->major;
>
>         if (auditd_test_task(tsk))
>                 return;
>
>         rcu_read_lock();
>         list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_EXIT], list) {
> -               if (audit_in_mask(&e->rule, ctx->major) &&
> +               if (audit_in_mask(&e->rule, major) &&
>                     audit_filter_rules(tsk, &e->rule, ctx, NULL,
>                                        &state, false)) {
>                         rcu_read_unlock();
> --
> 2.31.1

-- 
paul-moore.com