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Wed, 26 May 2021 03:19:17 -0700 (PDT) Received: from [192.168.8.197] ([85.255.235.102]) by smtp.gmail.com with ESMTPSA id u8sm5538665wmq.29.2021.05.26.03.19.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 May 2021 03:19:16 -0700 (PDT) To: Paul Moore , Jens Axboe 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: Pavel Begunkov Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring Message-ID: <0a668302-b170-31ce-1651-ddf45f63d02a@gmail.com> Date: Wed, 26 May 2021 11:19:08 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 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; 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charset="us-ascii" Content-Transfer-Encoding: 7bit On 5/26/21 3:04 AM, 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); > + } I'd rather agree that it's my cycle-picking. The case I care about is CONFIG_AUDIT=y (because everybody enable it), and io_uring tracing _not_ enabled at runtime. If enabled let them suffer the overhead, it will probably dip down the performance So, for the case I care about it's two of if (unlikely(audit_enabled && current->audit_context)) in the hot path. load-test-jump + current, so it will be around 7x2 instructions. We can throw away audit_enabled as you say systemd already enables it, that will give 4x2 instructions including 2 conditional jumps. That's not great at all. And that's why I brought up the question about need of pre and post hooks and whether can be combined. Would be just 4 instructions and that is ok (ish). > 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. I'm curious, why it's enabled by many distros by default? Are there use cases they use? Tempting to add AUDIT_IOURING=default N, but won't work I guess -- Pavel Begunkov -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit