secure_computing() should always be called first in syscall_trace(), and if it returns non-zero, we should stop further handling. Then that system call may eventually fail, be trapped or the process itself be killed depending on loaded rules.
This patch also defines specific system call numbers, __NR_seccomp_*, solely used by secure_computing() for seccomp mode 1 (only read, write, exit and sigreturn are allowd).
Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org --- arch/arm64/Kconfig | 17 +++++++++++++++++ arch/arm64/include/asm/seccomp.h | 28 ++++++++++++++++++++++++++++ arch/arm64/include/asm/unistd.h | 3 +++ arch/arm64/kernel/entry.S | 4 ++++ arch/arm64/kernel/ptrace.c | 5 +++++ 5 files changed, 57 insertions(+) create mode 100644 arch/arm64/include/asm/seccomp.h
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index a21455e..a0102f7 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -27,6 +27,7 @@ config ARM64 select HARDIRQS_SW_RESEND select HAVE_ARCH_AUDITSYSCALL select HAVE_ARCH_JUMP_LABEL + select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_TRACEHOOK select HAVE_DEBUG_BUGVERBOSE select HAVE_DEBUG_KMEMLEAK @@ -222,6 +223,22 @@ config HAVE_ARCH_TRANSPARENT_HUGEPAGE
source "mm/Kconfig"
+config SECCOMP + def_bool y + 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. + config XEN_DOM0 def_bool y depends on XEN diff --git a/arch/arm64/include/asm/seccomp.h b/arch/arm64/include/asm/seccomp.h new file mode 100644 index 0000000..3482155 --- /dev/null +++ b/arch/arm64/include/asm/seccomp.h @@ -0,0 +1,28 @@ +/* + * arch/arm64/include/asm/seccomp.h + * + * Copyright (C) 2014 Linaro Limited + * Author: AKASHI Takahiro takahiro.akashi@linaro.org + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ +#ifndef _ASM_SECCOMP_H +#define _ASM_SECCOMP_H + +#include <asm/unistd.h> + +#ifdef CONFIG_COMPAT +#define __NR_seccomp_read_32 __NR_compat_read +#define __NR_seccomp_write_32 __NR_compat_write +#define __NR_seccomp_exit_32 __NR_compat_exit +#define __NR_seccomp_sigreturn_32 __NR_compat_sigreturn +#endif /* CONFIG_COMPAT */ + +#define __NR_seccomp_read __NR_read +#define __NR_seccomp_write __NR_write +#define __NR_seccomp_exit __NR_exit +#define __NR_seccomp_sigreturn __NR_rt_sigreturn + +#endif /* _ASM_SECCOMP_H */ diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h index 4a09fdb..05f2db3 100644 --- a/arch/arm64/include/asm/unistd.h +++ b/arch/arm64/include/asm/unistd.h @@ -30,6 +30,9 @@ * Compat syscall numbers used by the AArch64 kernel. */ #define __NR_compat_restart_syscall 0 +#define __NR_compat_exit 1 +#define __NR_compat_read 3 +#define __NR_compat_write 4 #define __NR_compat_sigreturn 119 #define __NR_compat_rt_sigreturn 173
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 96c2d03..55d4e6c 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -651,6 +651,10 @@ __sys_trace: mov x1, sp mov w0, #0 // trace entry bl syscall_trace +#ifdef CONFIG_SECCOMP + cmp w0, #0 // check seccomp result + b.lt ret_to_user // -1 means 'rejected' +#endif adr lr, __sys_trace_return // return address uxtw scno, w0 // syscall number (possibly new) mov x1, sp // pointer to regs diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 8cdba09..3bfe398 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -26,6 +26,7 @@ #include <linux/smp.h> #include <linux/ptrace.h> #include <linux/user.h> +#include <linux/seccomp.h> #include <linux/security.h> #include <linux/init.h> #include <linux/signal.h> @@ -1064,6 +1065,10 @@ asmlinkage int syscall_trace(int dir, struct pt_regs *regs) { unsigned long saved_reg;
+ if (!dir && secure_computing((int)regs->syscallno)) + /* seccomp failures shouldn't expose any additional code. */ + return -1; + if (is_compat_task()) { /* AArch32 uses ip (r12) for scratch */ saved_reg = regs->regs[12];