ARM: SECCOMP support

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>

4 files changed, 40 insertions, 2 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 88c97bc7a6f5..1273ee8756be 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1463,6 +1463,20 @@ config UACCESS_WITH_MEMCPY
           However, if the CPU data cache is using a write-allocate mode,
           this option is unlikely to provide any performance gain.
 
+config SECCOMP
+        bool
+        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.
+
 config CC_STACKPROTECTOR
         bool "Enable -fstack-protector buffer overflow detection (EXPERIMENTAL)"
         help
diff --git a/arch/arm/include/asm/seccomp.h b/arch/arm/include/asm/seccomp.h
new file mode 100644
index 000000000000..52b156b341f5
--- /dev/null
+++ b/arch/arm/include/asm/seccomp.h
@@ -0,0 +1,11 @@
+#ifndef _ASM_ARM_SECCOMP_H
+#define _ASM_ARM_SECCOMP_H
+
+#include <linux/unistd.h>
+
+#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_ARM_SECCOMP_H */
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 763e29fa8530..7b5cc8dae06e 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -144,6 +144,7 @@ extern void vfp_flush_hwstate(struct thread_info *);
 #define TIF_MEMDIE              18      /* is terminating due to OOM killer */
 #define TIF_FREEZE              19
 #define TIF_RESTORE_SIGMASK     20
+#define TIF_SECCOMP             21
 
 #define _TIF_SIGPENDING         (1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED       (1 << TIF_NEED_RESCHED)
@@ -153,6 +154,7 @@ extern void vfp_flush_hwstate(struct thread_info *);
 #define _TIF_USING_IWMMXT       (1 << TIF_USING_IWMMXT)
 #define _TIF_FREEZE             (1 << TIF_FREEZE)
 #define _TIF_RESTORE_SIGMASK    (1 << TIF_RESTORE_SIGMASK)
+#define _TIF_SECCOMP            (1 << TIF_SECCOMP)
 
 /*
  * Change these and you break ASM code in entry-common.S
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 7885722bdf4e..0385a8207b67 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -295,7 +295,6 @@ ENTRY(vector_swi)
 
         get_thread_info tsk
         adr     tbl, sys_call_table             @ load syscall table pointer
-        ldr     ip, [tsk, #TI_FLAGS]            @ check for syscall tracing
 
 #if defined(CONFIG_OABI_COMPAT)
         /*
@@ -312,8 +311,20 @@ ENTRY(vector_swi)
         eor     scno, scno, #__NR_SYSCALL_BASE  @ check OS number
 #endif
 
+        ldr     r10, [tsk, #TI_FLAGS]           @ check for syscall tracing
         stmdb   sp!, {r4, r5}                   @ push fifth and sixth args
-        tst     ip, #_TIF_SYSCALL_TRACE         @ are we tracing syscalls?
+
+#ifdef CONFIG_SECCOMP
+        tst     r10, #_TIF_SECCOMP
+        beq     1f
+        mov     r0, scno
+        bl      __secure_computing      
+        add     r0, sp, #S_R0 + S_OFF           @ pointer to regs
+        ldmia   r0, {r0 - r3}                   @ have to reload r0 - r3
+1:
+#endif
+
+        tst     r10, #_TIF_SYSCALL_TRACE                @ are we tracing syscalls?
         bne     __sys_trace
 
         cmp     scno, #NR_syscalls              @ check upper syscall limit