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Thu, 08 Oct 2020 21:47:28 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: YiFei Zhu Date: Thu, 8 Oct 2020 23:47:17 -0500 Message-ID: Subject: Re: [PATCH v3 seccomp 2/5] seccomp/cache: Add "emulator" to check if filter is constant allow To: Linux Containers Cc: YiFei Zhu , bpf , kernel list , Aleksa Sarai , Andrea Arcangeli , Andy Lutomirski , David Laight , Dimitrios Skarlatos , Giuseppe Scrivano , Hubertus Franke , Jack Chen , Jann Horn , Josep Torrellas , Kees Cook , Tianyin Xu , Tobin Feldman-Fitzthum , Tycho Andersen , Valentin Rothberg , Will Drewry Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 30, 2020 at 10:20 AM YiFei Zhu wrote: > @@ -544,7 +577,8 @@ static struct seccomp_filter *seccomp_prepare_filter(= struct sock_fprog *fprog) > { > struct seccomp_filter *sfilter; > int ret; > - const bool save_orig =3D IS_ENABLED(CONFIG_CHECKPOINT_RESTORE); > + const bool save_orig =3D IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) || > + IS_ENABLED(CONFIG_SECCOMP_CACHE_NR_ONLY); > > if (fprog->len =3D=3D 0 || fprog->len > BPF_MAXINSNS) > return ERR_PTR(-EINVAL); I'm trying to use __is_defined(SECCOMP_ARCH_NATIVE) here, and got this mess= age: kernel/seccomp.c: In function =E2=80=98seccomp_prepare_filter=E2=80=99: ././include/linux/kconfig.h:44:44: error: pasting "__ARG_PLACEHOLDER_" and "(" does not give a valid preprocessing token 44 | #define ___is_defined(val) ____is_defined(__ARG_PLACEHOLDER_##val) | ^~~~~~~~~~~~~~~~~~ ././include/linux/kconfig.h:43:27: note: in expansion of macro =E2=80=98___= is_defined=E2=80=99 43 | #define __is_defined(x) ___is_defined(x) | ^~~~~~~~~~~~~ kernel/seccomp.c:629:11: note: in expansion of macro =E2=80=98__is_defined= =E2=80=99 629 | __is_defined(SECCOMP_ARCH_NATIVE); | ^~~~~~~~~~~~ Looking at the implementation of __is_defined, it is: #define __ARG_PLACEHOLDER_1 0, #define __take_second_arg(__ignored, val, ...) val #define __is_defined(x) ___is_defined(x) #define ___is_defined(val) ____is_defined(__ARG_PLACEHOLDER_##val) #define ____is_defined(arg1_or_junk) __take_second_arg(arg1_or_junk 1, 0) Hence, when FOO is defined to be 1, then the expansion would be __is_defined(FOO) -> ___is_defined(1) -> ____is_defined(__ARG_PLACEHOLDER_1) -> __take_second_arg(0, 1, 0) -> 1, and when FOO is not defined, the expansion would be __is_defined(FOO) -> ___is_defined(FOO) -> ____is_defined(__ARG_PLACEHOLDER_FOO) -> __take_second_arg(__ARG_PLACEHOLDER_FOO 1, 0) -> 0 However, here SECCOMP_ARCH_NATIVE is an expression from an OR of some bits, and __is_defined(SECCOMP_ARCH_NATIVE) would not expand to __ARG_PLACEHOLDER_1 during any stage in the preprocessing. Is there any better way to do this? I'm thinking of just doing #if defined(CONFIG_CHECKPOINT_RESTORE) || defined(SECCOMP_ARCH_NATIVE) like in Kee's patch. YiFei Zhu