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Wed, 26 May 2021 10:15:25 -0700 (PDT) Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring 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> From: Jens Axboe Message-ID: <9e69e4b6-2b87-a688-d604-c7f70be894f5@kernel.dk> Date: Wed, 26 May 2021 11:15:24 -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: 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 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 10.5.11.15 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 5/25/21 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! >> aio never had any audit logging as far as I can tell. I think it'd make >> a lot more sense to selectively enable audit logging only for opcodes >> that we care about. File open/create/unlink/mkdir etc, that kind of >> thing. File level operations that people would care about logging. Would >> they care about logging a buffer registration or a polled read from a >> device/file? I highly doubt it, and we don't do that for alternative >> methods either. Doesn't really make sense for a lot of the other >> operations, imho. > > We would need to check with the current security requirements (there > are distro people on the linux-audit list that keep track of that > stuff), but looking at the opcodes right now my gut feeling is that > most of the opcodes would be considered "security relevant" so > selective auditing might not be that useful in practice. It would > definitely clutter the code and increase the chances that new opcodes > would not be properly audited when they are merged. We don't audit read/write from aio, as mentioned. In the past two decades, I take it that hasn't been a concern? I agree that some opcodes should _definitely_ be audited. Things like opening a file, closing a file, removing/creating a file, mount, etc. But normal read/write, I think that's just utter noise and not useful at all. Auditing on a per-opcode basis is trivial, io_uring already has provisions for flagging opcode requirements and this would just be another one. -- Jens Axboe -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit