Hi Kees, On Wed, Oct 28, 2020 at 1:06 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Tue, Oct 27, 2020 at 10:52:39AM +0100, Geert Uytterhoeven wrote: > > 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 descriptions are outdated; they talk about /proc rather than 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 have an outdated depend on PROC_FS and this dependency is removed 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 Mostly "server" and "desktop" platforms. > via defconfig, roughly speaking: > > arm > arm64 > sh Note that these defconfigs are example configs, not meant for production. E.g. arm/multi_v7_defconfig and arm64/defconfig enable about everything for compile coverage. > 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? Having support does not necessarily imply you want it enabled. If systemd needs it (does it? I have Debian nfsroots with systemd, without SECCOMP), you can enable it in the defconfig. "Default y" is for things you cannot do without, unless you know better. Bloat-o-meter says enabling SECCOMP consumes only ca. 8 KiB (on arm32), so perhaps "default y if !EXPERT"? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
