On Tue, Oct 27, 2020 at 10:52:39AM +0100, Geert Uytterhoeven wrote: > Hi Yifei, > > On Thu, Sep 24, 2020 at 2:48 PM YiFei Zhu <zhuyifei1999@xxxxxxxxx> wrote: > > From: YiFei Zhu <yifeifz2@xxxxxxxxxxxx> > > > > In order to make adding configurable features into seccomp > > easier, it's better to have the options at one single location, > > considering easpecially that the bulk of seccomp code is > > arch-independent. An quick look also show that many SECCOMP > > descriptions are outdated; they talk about /proc rather than > > prctl. > > > > As a result of moving the config option and keeping it default > > on, architectures arm, arm64, csky, riscv, sh, and xtensa > > did not have SECCOMP on by default prior to this and SECCOMP will > > be default in this change. > > > > Architectures microblaze, mips, powerpc, s390, sh, and sparc > > have an outdated depend on PROC_FS and this dependency is removed > > in this change. > > > > Suggested-by: Jann Horn <jannh@xxxxxxxxxx> > > Link: https://lore.kernel.org/lkml/CAG48ez1YWz9cnp08UZgeieYRhHdqh-ch7aNwc4JRBnGyrmgfMg@xxxxxxxxxxxxxx/ > > Signed-off-by: YiFei Zhu <yifeifz2@xxxxxxxxxxxx> > > Thanks for your patch. which is now commit 282a181b1a0d66de ("seccomp: > Move config option SECCOMP to arch/Kconfig") in v5.10-rc1. > > > --- a/arch/Kconfig > > +++ b/arch/Kconfig > > @@ -458,6 +462,23 @@ config HAVE_ARCH_SECCOMP_FILTER > > results in the system call being skipped immediately. > > - seccomp syscall wired up > > > > +config SECCOMP > > + def_bool y > > + depends on HAVE_ARCH_SECCOMP > > + prompt "Enable seccomp to safely compute untrusted bytecode" > > + help > > + This kernel feature is useful for number crunching applications > > + that may need to compute untrusted bytecode during their > > + execution. By using pipes or other transports made available to > > + the process as file descriptors supporting the read/write > > + syscalls, it's possible to isolate those applications in > > + their own address space using seccomp. Once seccomp is > > + enabled via prctl(PR_SET_SECCOMP), it cannot be disabled > > + and the task is only allowed to execute a few safe syscalls > > + defined by each seccomp mode. > > + > > + If unsure, say Y. Only embedded should say N here. > > + > > Please tell me why SECCOMP is special, and deserves to default to be > enabled. Is it really that critical, given only 13.5 (half of sparc > ;-) out of 24 > architectures implement support for it? That's an excellent point; I missed this in my review as I saw several Kconfig already marked "def_bool y" but failed to note it wasn't _all_ of them. Okay, checking before this patch, these had them effectively enabled: via Kconfig: parisc s390 um x86 via defconfig, roughly speaking: arm arm64 sh How about making the default depend on HAVE_ARCH_SECCOMP_FILTER? These have SECCOMP_FILTER support: arch/arm/Kconfig: select HAVE_ARCH_SECCOMP_FILTER if AEABI && !OABI_COMPAT arch/arm64/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/csky/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/mips/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/parisc/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/powerpc/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/riscv/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/s390/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/sh/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/um/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/x86/Kconfig: select HAVE_ARCH_SECCOMP_FILTER arch/xtensa/Kconfig: select HAVE_ARCH_SECCOMP_FILTER So the "new" promotions would be: csky mips powerpc riscv xtensa Which would leave only these two: arch/microblaze/Kconfig: select HAVE_ARCH_SECCOMP arch/sparc/Kconfig: select HAVE_ARCH_SECCOMP if SPARC64 At this point, given the ubiquity of seccomp usage (e.g. systemd), I guess it's not unreasonable to make it def_bool y? I'm open to suggestions! -- Kees Cook
