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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id b20sm3775348pfb.198.2020.09.30.15.59.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Sep 2020 15:59:38 -0700 (PDT) Date: Wed, 30 Sep 2020 15:59:37 -0700 From: Kees Cook To: YiFei Zhu Cc: containers@lists.linux-foundation.org, YiFei Zhu , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Aleksa Sarai , Andrea Arcangeli , Andy Lutomirski , David Laight , Dimitrios Skarlatos , Giuseppe Scrivano , Hubertus Franke , Jack Chen , Jann Horn , Josep Torrellas , Tianyin Xu , Tobin Feldman-Fitzthum , Tycho Andersen , Valentin Rothberg , Will Drewry Subject: Re: [PATCH v3 seccomp 5/5] seccomp/cache: Report cache data through /proc/pid/seccomp_cache Message-ID: <202009301554.590642EBE@keescook> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Sep 30, 2020 at 10:19:16AM -0500, YiFei Zhu wrote: > From: YiFei Zhu > > Currently the kernel does not provide an infrastructure to translate > architecture numbers to a human-readable name. Translating syscall > numbers to syscall names is possible through FTRACE_SYSCALL > infrastructure but it does not provide support for compat syscalls. > > This will create a file for each PID as /proc/pid/seccomp_cache. > The file will be empty when no seccomp filters are loaded, or be > in the format of: > > where ALLOW means the cache is guaranteed to allow the syscall, > and filter means the cache will pass the syscall to the BPF filter. > > For the docker default profile on x86_64 it looks like: > x86_64 0 ALLOW > x86_64 1 ALLOW > x86_64 2 ALLOW > x86_64 3 ALLOW > [...] > x86_64 132 ALLOW > x86_64 133 ALLOW > x86_64 134 FILTER > x86_64 135 FILTER > x86_64 136 FILTER > x86_64 137 ALLOW > x86_64 138 ALLOW > x86_64 139 FILTER > x86_64 140 ALLOW > x86_64 141 ALLOW > [...] > > This file is guarded by CONFIG_DEBUG_SECCOMP_CACHE with a default > of N because I think certain users of seccomp might not want the > application to know which syscalls are definitely usable. For > the same reason, it is also guarded by CAP_SYS_ADMIN. > > Suggested-by: Jann Horn > Link: https://lore.kernel.org/lkml/CAG48ez3Ofqp4crXGksLmZY6=fGrF_tWyUCg7PBkAetvbbOPeOA@mail.gmail.com/ > Signed-off-by: YiFei Zhu > --- > arch/Kconfig | 15 +++++++++++ > arch/x86/include/asm/seccomp.h | 3 +++ > fs/proc/base.c | 3 +++ > include/linux/seccomp.h | 5 ++++ > kernel/seccomp.c | 46 ++++++++++++++++++++++++++++++++++ > 5 files changed, 72 insertions(+) > > diff --git a/arch/Kconfig b/arch/Kconfig > index ca867b2a5d71..b840cadcc882 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -478,6 +478,7 @@ config HAVE_ARCH_SECCOMP_CACHE_NR_ONLY > - all the requirements for HAVE_ARCH_SECCOMP_FILTER > - SECCOMP_ARCH_DEFAULT > - SECCOMP_ARCH_DEFAULT_NR > + - SECCOMP_ARCH_DEFAULT_NAME > > config SECCOMP > prompt "Enable seccomp to safely execute untrusted bytecode" > @@ -532,6 +533,20 @@ config SECCOMP_CACHE_NR_ONLY > > endchoice > > +config DEBUG_SECCOMP_CACHE naming nit: I prefer where what how order, so SECCOMP_CACHE_DEBUG. > + bool "Show seccomp filter cache status in /proc/pid/seccomp_cache" > + depends on SECCOMP_CACHE_NR_ONLY > + depends on PROC_FS > + help > + This is enables /proc/pid/seccomp_cache interface to monitor > + seccomp cache data. The file format is subject to change. Reading > + the file requires CAP_SYS_ADMIN. > + > + This option is for debugging only. Enabling present the risk that > + an adversary may be able to infer the seccomp filter logic. > + > + If unsure, say N. > + > config HAVE_ARCH_STACKLEAK > bool > help > diff --git a/arch/x86/include/asm/seccomp.h b/arch/x86/include/asm/seccomp.h > index 7b3a58271656..33ccc074be7a 100644 > --- a/arch/x86/include/asm/seccomp.h > +++ b/arch/x86/include/asm/seccomp.h > @@ -19,13 +19,16 @@ > #ifdef CONFIG_X86_64 > # define SECCOMP_ARCH_DEFAULT AUDIT_ARCH_X86_64 > # define SECCOMP_ARCH_DEFAULT_NR NR_syscalls > +# define SECCOMP_ARCH_DEFAULT_NAME "x86_64" > # ifdef CONFIG_COMPAT > # define SECCOMP_ARCH_COMPAT AUDIT_ARCH_I386 > # define SECCOMP_ARCH_COMPAT_NR IA32_NR_syscalls > +# define SECCOMP_ARCH_COMPAT_NAME "x86_32" I think this should be "ia32"? Is there a good definitive guide on this naming convention? -- Kees Cook