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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=y5hc1lB5zTME3aYydIbRBcof2PiNcOpgJpiSa1+Oo68=; b=Rmwlf+G1HLQVA1sgNTEpv17o5dXlBUst1q/LVcuqRaNMj0ydhrJXAElhFBGf8u68zM 9JWgRMpEa+Hkc5lMzySP/0a72MlrlT2giE3kzXMOHS5rWp/Kp8KwOQ+P+Z5MpecV5S3Y l93F18EZpxgatvUIzFUjJmZ8EdfTGXHsK1xF1kpNstseRXkJpMPzSF86MOH3pql8aKgc JxA2OZu9BBw1txBlIpoWzipH0XVvZ1Njr583o0+PaxZIN0H21jBdxcQt9gGXkHABcssk hSmr6Va1FrvtPA0+CubaQE1mhD/l/tv+x3JraHKhsc4ZFmIl/H8+2QZqOjGNDS+9ws9n 9sxg== X-Gm-Message-State: AOAM530sJCbl90+FIirTSa8MPkwXvpgKR3Pq8ZnUiIRlztB5MKcSZ8bl 3C0waUtRS0ETw3Gqmk9QMz4NC/+5Cr5FoiaevqWY X-Google-Smtp-Source: ABdhPJx3f2fYRf1XUrHxqhJbfeRNdB4G8SDETCWKvTSo/6QYapX3mqm70ppiB1uPLoMxAzlsWe8ZlResAmsGsBGMdjo= X-Received: by 2002:a17:906:9e21:: with SMTP id fp33mr34926566ejc.488.1622054680028; Wed, 26 May 2021 11:44:40 -0700 (PDT) MIME-Version: 1.0 References: <162163367115.8379.8459012634106035341.stgit@sifl> <162163379461.8379.9691291608621179559.stgit@sifl> <162219f9-7844-0c78-388f-9b5c06557d06@gmail.com> <8943629d-3c69-3529-ca79-d7f8e2c60c16@kernel.dk> <9e69e4b6-2b87-a688-d604-c7f70be894f5@kernel.dk> <3bef7c8a-ee70-d91d-74db-367ad0137d00@kernel.dk> In-Reply-To: From: Paul Moore Date: Wed, 26 May 2021 14:44:29 -0400 Message-ID: Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring To: Jens Axboe X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-loop: linux-audit@redhat.com Cc: selinux@vger.kernel.org, io-uring@vger.kernel.org, linux-security-module@vger.kernel.org, linux-audit@redhat.com, Kumar Kartikeya Dwivedi , linux-fsdevel@vger.kernel.org, Pavel Begunkov , Alexander Viro X-BeenThere: linux-audit@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: Linux Audit Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-audit-bounces@redhat.com Errors-To: linux-audit-bounces@redhat.com X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=linux-audit-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Wed, May 26, 2021 at 2:01 PM Jens Axboe wrote: > On 5/26/21 11:54 AM, Jens Axboe wrote: > > On 5/26/21 11:31 AM, Jens Axboe wrote: > >> On 5/26/21 11:15 AM, Jens Axboe wrote: > >>> On 5/25/21 8:04 PM, Paul Moore wrote: > >>>> On Tue, May 25, 2021 at 9:11 PM Jens Axboe wrote: > >>>>> On 5/24/21 1:59 PM, Paul Moore wrote: > >>>>>> That said, audit is not for everyone, and we have build time and > >>>>>> runtime options to help make life easier. Beyond simply disabling > >>>>>> audit at compile time a number of Linux distributions effectively > >>>>>> shortcut audit at runtime by adding a "never" rule to the audit > >>>>>> filter, for example: > >>>>>> > >>>>>> % auditctl -a task,never > >>>>> > >>>>> As has been brought up, the issue we're facing is that distros have > >>>>> CONFIG_AUDIT=y and hence the above is the best real world case outside > >>>>> of people doing custom kernels. My question would then be how much > >>>>> overhead the above will add, considering it's an entry/exit call per op. > >>>>> If auditctl is turned off, what is the expectation in turns of overhead? > >>>> > >>>> I commented on that case in my last email to Pavel, but I'll try to go > >>>> over it again in a little more detail. > >>>> > >>>> As we discussed earlier in this thread, we can skip the req->opcode > >>>> check before both the _entry and _exit calls, so we are left with just > >>>> the bare audit calls in the io_uring code. As the _entry and _exit > >>>> functions are small, I've copied them and their supporting functions > >>>> below and I'll try to explain what would happen in CONFIG_AUDIT=y, > >>>> "task,never" case. > >>>> > >>>> + static inline struct audit_context *audit_context(void) > >>>> + { > >>>> + return current->audit_context; > >>>> + } > >>>> > >>>> + static inline bool audit_dummy_context(void) > >>>> + { > >>>> + void *p = audit_context(); > >>>> + return !p || *(int *)p; > >>>> + } > >>>> > >>>> + static inline void audit_uring_entry(u8 op) > >>>> + { > >>>> + if (unlikely(audit_enabled && audit_context())) > >>>> + __audit_uring_entry(op); > >>>> + } > >>>> > >>>> We have one if statement where the conditional checks on two > >>>> individual conditions. The first (audit_enabled) is simply a check to > >>>> see if anyone has "turned on" auditing at runtime; historically this > >>>> worked rather well, and still does in a number of places, but ever > >>>> since systemd has taken to forcing audit on regardless of the admin's > >>>> audit configuration it is less useful. The second (audit_context()) > >>>> is a check to see if an audit_context has been allocated for the > >>>> current task. In the case of "task,never" current->audit_context will > >>>> be NULL (see audit_alloc()) and the __audit_uring_entry() slowpath > >>>> will never be called. > >>>> > >>>> Worst case here is checking the value of audit_enabled and > >>>> current->audit_context. Depending on which you think is more likely > >>>> we can change the order of the check so that the > >>>> current->audit_context check is first if you feel that is more likely > >>>> to be NULL than audit_enabled is to be false (it may be that way now). > >>>> > >>>> + static inline void audit_uring_exit(int success, long code) > >>>> + { > >>>> + if (unlikely(!audit_dummy_context())) > >>>> + __audit_uring_exit(success, code); > >>>> + } > >>>> > >>>> The exit call is very similar to the entry call, but in the > >>>> "task,never" case it is very simple as the first check to be performed > >>>> is the current->audit_context check which we know to be NULL. The > >>>> __audit_uring_exit() slowpath will never be called. > >>> > >>> I actually ran some numbers this morning. The test base is 5.13+, and > >>> CONFIG_AUDIT=y and CONFIG_AUDITSYSCALL=y is set for both the baseline > >>> test and the test with this series applied. I used your git branch as of > >>> this morning. > >>> > >>> The test case is my usual peak perf test, which is random reads at > >>> QD=128 and using polled IO. It's a single core test, not threaded. I ran > >>> two different tests - one was having a thread just do the IO, the other > >>> is using SQPOLL to do the IO for us. The device is capable than more > >>> IOPS than a single core can deliver, so we're CPU limited in this test. > >>> Hence it's a good test case as it does actual work, and shows software > >>> overhead quite nicely. Runs are very stable (less than 0.5% difference > >>> between runs on the same base), yet I did average 4 runs. > >>> > >>> Kernel SQPOLL IOPS Perf diff > >>> --------------------------------------------------------- > >>> 5.13 0 3029872 0.0% > >>> 5.13 1 3031056 0.0% > >>> 5.13 + audit 0 2894160 -4.5% > >>> 5.13 + audit 1 2886168 -4.8% > >>> > >>> That's an immediate drop in perf of almost 5%. Looking at a quick > >>> profile of it (nothing fancy, just checking for 'audit' in the profile) > >>> shows this: > >>> > >>> + 2.17% io_uring [kernel.vmlinux] [k] __audit_uring_entry > >>> + 0.71% io_uring [kernel.vmlinux] [k] __audit_uring_exit > >>> 0.07% io_uring [kernel.vmlinux] [k] __audit_syscall_entry > >>> 0.02% io_uring [kernel.vmlinux] [k] __audit_syscall_exit > >>> > >>> Note that this is with _no_ rules! > >> > >> io_uring also supports a NOP command, which basically just measures > >> reqs/sec through the interface. Ran that as well: > >> > >> Kernel SQPOLL IOPS Perf diff > >> --------------------------------------------------------- > >> 5.13 0 31.05M 0.0% > >> 5.13 + audit 0 25.31M -18.5% > >> > >> and profile for the latter includes: > >> > >> + 5.19% io_uring [kernel.vmlinux] [k] __audit_uring_entry > >> + 4.31% io_uring [kernel.vmlinux] [k] __audit_uring_exit > >> 0.26% io_uring [kernel.vmlinux] [k] __audit_syscall_entry > >> 0.08% io_uring [kernel.vmlinux] [k] __audit_syscall_exit > > > > As Pavel correctly pointed it, looks like auditing is enabled. And > > indeed it was! Hence the above numbers is without having turned off > > auditing. Running the NOPs after having turned off audit, we get 30.6M > > IOPS, which is down about 1.5% from the baseline. The results for the > > polled random read test above did _not_ change from this, they are still > > down the same amount. > > > > Note, and I should have included this in the first email, this is not > > any kind of argument for or against audit logging. It's purely meant to > > be a set of numbers that show how the current series impacts > > performance. > > And finally, just checking if we make it optional per opcode if we see > any real impact, and the answer is no. Using the below patch which > effectively bypasses audit calls unless the opcode has flagged the need > to do so, I cannot measure any difference in perf (as expected). > > To turn this into something useful, my suggestion as a viable path > forward would be: > > 1) Use something like the below patch and flag request types that we > want to do audit logging for. > > 2) As Pavel suggested, eliminate the need for having both and entry/exit > hook, turning it into just one. That effectively cuts the number of > checks and calls in half. I suspect the updated working-io_uring branch with HEAD at 1f25193a3f54 (updated a short time ago, see my last email in this thread) will improve performance. Also, as has been mention several times now, for audit to work we need both the _entry and _exit call. -- paul moore www.paul-moore.com -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit