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[77.56.209.237]) by smtp.gmail.com with ESMTPSA id m5sm8001072wmg.13.2020.03.27.08.06.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Mar 2020 08:06:39 -0700 (PDT) From: KP Singh X-Google-Original-From: KP Singh Date: Fri, 27 Mar 2020 16:06:37 +0100 To: Alexei Starovoitov Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-security-module@vger.kernel.org, Brendan Jackman , Florent Revest , Alexei Starovoitov , Daniel Borkmann , James Morris , Kees Cook , Paul Turner , Jann Horn , Florent Revest , Brendan Jackman , Greg Kroah-Hartman Subject: Re: [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and execution Message-ID: <20200327150637.GA23032@chromium.org> References: <20200326142823.26277-1-kpsingh@chromium.org> <20200326142823.26277-5-kpsingh@chromium.org> <20200327031256.vhk2luomxgex3ui4@ast-mbp> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200327031256.vhk2luomxgex3ui4@ast-mbp> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On 26-Mär 20:12, Alexei Starovoitov wrote: > On Thu, Mar 26, 2020 at 03:28:19PM +0100, KP Singh wrote: > > > > if (arg == nr_args) { > > - if (prog->expected_attach_type == BPF_TRACE_FEXIT) { > > + /* BPF_LSM_MAC programs only have int and void functions they > > + * can be attached to. When they are attached to a void function > > + * they result in the creation of an FEXIT trampoline and when > > + * to a function that returns an int, a MODIFY_RETURN > > + * trampoline. > > + */ > > + if (prog->expected_attach_type == BPF_TRACE_FEXIT || > > + prog->expected_attach_type == BPF_LSM_MAC) { > > if (!t) > > return true; > > t = btf_type_by_id(btf, t->type); > > Could you add a comment here that though BPF_MODIFY_RETURN-like check > if (ret_type != 'int') return -EINVAL; > is _not_ done here. It is still safe, since LSM hooks have only > void and int return types. Good idea, I reworded the comment to make this explicit and moved the comment to inside the if condition. > > > + case BPF_LSM_MAC: > > + if (!prog->aux->attach_func_proto->type) > > + /* The function returns void, we cannot modify its > > + * return value. > > + */ > > + return BPF_TRAMP_FEXIT; > > + else > > + return BPF_TRAMP_MODIFY_RETURN; > > I was thinking whether it would help performance significantly enough > if we add a flavor of BPF_TRAMP_FEXIT that doesn't have > BPF_TRAMP_F_CALL_ORIG. Agreed. > That will save the cost of nop call, but I guess indirect call due > to lsm infra is slow enough, so this extra few cycles won't be noticeable. > So I'm fine with it as-is. When lsm hooks will get rid of indirect call > we can optimize it further. Also agreed, that's the next step. :) - KP