From: Andy Lutomirski Subject: General flags to turn things off (getrandom, pid lookup, etc) Date: Fri, 25 Jul 2014 11:30:48 -0700 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 To: "Eric W. Biederman" , Julien Tinnes , David Drysdale , Al Viro , Paolo Bonzini , LSM List , Greg Kroah-Hartman , Paul Moore , James Morris , Linux API , Meredydd Luff , Christoph Hellwig , "linux-kernel@vger.kernel.org" , Kees Cook , "Theodore Ts'o" , Andy Lutomirski , Henrique de Moraes Holschuh , linux-crypto@vger.kernel.org Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org [new thread because this sort of combines two threads] There is recent interest in having a way to turn generally-available kernel features off. Maybe we should add a good one so we can stop bikeshedding and avoid proliferating dumb interfaces. Things that might want to be turn-off-able include: - getrandom with GRND_RANDOM [from the getrandom threads] - Any lookup of a non-self pid [from the capsicum thread] - Any lookup of a pid outside the caller thread group [capsicum] - Various architectural things (personal wishlist), e.g.: - RDTSC and userspace HPET access - CPUID? - 32-bit GDT code segments [huge attack surface] - 64-bit GDT code segments [probably pointless] I would propose a new syscall for this: long restrict_userspace(int mode, int type, int value, int flags); mode is RESTRICT_SET, RESTRICT_GET, or RESTRICT_LOCK. type is RESTRICT_GRND_RANDOM, RESTRICT_PID_SCOPE, RESTRICT_X86_TIMING, etc. Value is zero if RESTRICT_GET. Otherwise value is the desired value, generally 0 or 1. For RESTRICT_PID_SCOPE, value would be RESTRICT_PID_SCOPE_ANY, RESTRICT_PID_SCOPE_THREADGROUP, or RESTRICT_PID_SCOPE_SELF. flags must be zero. Someday, someone will propose a thread-sync flag. restrict_userspace requires either no_new_privs or CAP_SYS_ADMIN in the current user namespace. Thoughts? --Andy -- Andy Lutomirski AMA Capital Management, LLC