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Wed, 26 May 2021 10:31:49 -0700 (PDT) Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring From: Jens Axboe To: Paul Moore 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> Message-ID: <3bef7c8a-ee70-d91d-74db-367ad0137d00@kernel.dk> Date: Wed, 26 May 2021 11:31:48 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <9e69e4b6-2b87-a688-d604-c7f70be894f5@kernel.dk> 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 10.11.54.6 X-loop: linux-audit@redhat.com X-Mailman-Approved-At: Wed, 26 May 2021 13:50:52 -0400 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 2.79 on 10.5.11.14 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-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 -- Jens Axboe -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit