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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=4yBeE8Xf/Fq4mUnYlQxVkTLJf9hFbr354bGFzsYff5g=; b=KLwMfoWEStEMnz4jExxMnzfLHeK1qWgRpIXDqyf3qJK0Z15yx2NdLPkrxPfJA8R7ng eMOJeR5HjU4eXGwAwwsojtSg1iXKEiNgfUV/4+81tpngjvfOZnas10gUtA7nHYWiLMkJ U8t7+I1j02Ur3/BrelMkSoPjbUwjllAMEuciJY6qmzQOVZ8m5WKgNFrGtvkdmzNlpZvb YrGJU6JYklzZcpEnKinrSfZJKqv9zIz8Q8SF8YExgGB5oiQivBhWr2k+dbflSLpnZQHu 4afHPacAZvtP7gZUSEeJNLaF8OHivxmV6CTfD+GORpUFOkm//y/Q2Fbo+QukjxkUAW/e 05lA== X-Gm-Message-State: AOAM530XfB72zJn3W+xXEicUvA53F8TAf42D/0AWfD5f+lmrVaT23JsU oLc7WlZvBk5N6iTquTyHHR6RpNi/mlLiQRd+nIKt X-Google-Smtp-Source: ABdhPJzYmCCVE+5LIwHiiKYytbKEjjju7Fqmoh+e+Ii4nBCArjGV+iGuobXs1xR1zjMey8kMg7YjXMHDgqh8jPFVbhw= X-Received: by 2002:aa7:c7cd:: with SMTP id o13mr15720410eds.269.1622039929256; Wed, 26 May 2021 07:38:49 -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> <0a668302-b170-31ce-1651-ddf45f63d02a@gmail.com> In-Reply-To: <0a668302-b170-31ce-1651-ddf45f63d02a@gmail.com> From: Paul Moore Date: Wed, 26 May 2021 10:38:38 -0400 Message-ID: Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring To: Pavel Begunkov 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 10.11.54.4 X-loop: linux-audit@redhat.com Cc: Jens Axboe , selinux@vger.kernel.org, linux-security-module@vger.kernel.org, linux-audit@redhat.com, Kumar Kartikeya Dwivedi , linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, 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 6:19 AM Pavel Begunkov wrote: > 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. We've basically got it down to the equivalent of two "current->audit_context != NULL" checks in the case where audit is built into the kernel but disabled at runtime, e.g. CONFIG_AUDIT=y and "task,never". I'm at a loss for how we can lower the overhead any further, but I'm open to suggestions. > 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). As discussed previously in this thread that isn't really an option from an audit perspective. > > 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? We've already talked about certain users and environments where audit is an important requirement, e.g. public sector, health care, financial institutions, etc.; without audit Linux wouldn't be an option for these users, at least not without heavy modification, out-of-tree/ISV patches, etc. I currently don't have any direct ties to any distros, "Enterprise" or otherwise, but in the past it has been my experience that distros much prefer to have a single kernel build to address the needs of all their users. In the few cases I have seen where a second kernel build is supported it is usually for hardware enablement. I'm sure there are other cases too, I just haven't seen them personally; the big distros definitely seem to have a strong desire to limit the number of supported kernel configs/builds. > Tempting to add AUDIT_IOURING=default N, but won't work I guess One of the nice things about audit is that it can give you a history of what a user did on a system, which is very important for a number of use cases. If we selectively disable audit for certain subsystems we create a blind spot in the audit log, and in the case of io_uring this can be a very serious blind spot. I fear that if we can't come to some agreement here we will need to make io_uring and audit mutually exclusive at build time which would be awful; forcing many distros to either make a hard choice or carry out-of-tree patches. -- paul moore www.paul-moore.com -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit