CHROMIUM: arch/arm: move secure_computing into trace; respect return code

There is very little difference in the TIF_SECCOMP and TIF_SYSCALL_TRACE
patsh in entry-common.S. In order to add support for
CONFIG_HAVE_ARCH_SECCOMP_FILTER without mangling the assembly too
badly, seccomp was moved into the syscall_trace() handler.

Additionally, the return value for secure_computing() is now checked
and a -1 value will result in the system call being skipped.

(Reworked for 3.4 merge to just piggyback on the audit enter path.)

Signed-off-by: Will Drewry <wad@chromium.org>

BUG=chromium-os:27878
TEST=compiles for arm. Need to test on a live machine.

Change-Id: I9493f28c30356a10eccb320e0a2d1a141388af9a
Reviewed-on: https://gerrit.chromium.org/gerrit/21376


Reviewed-by: Will Drewry <wad@chromium.org>
Tested-by: Will Drewry <wad@chromium.org>
Signed-off-by: Sasha Levitskiy <sanek@google.com>

arch/arm/kernel/entry-common.S

@@ -444,12 +444,7 @@ ENTRY(vector_swi)
 
 #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:
+	bne	__sys_trace
 #endif
 
 	tst	r10, #_TIF_SYSCALL_WORK		@ are we tracing syscalls?

arch/arm/kernel/ptrace.c

@@ -909,19 +909,28 @@ long arch_ptrace(struct task_struct *child, long request,
 asmlinkage int syscall_trace(int why, struct pt_regs *regs, int scno)
 {
 	unsigned long ip;
+	current_thread_info()->syscall = scno;
 
 	if (why)
 		audit_syscall_exit(regs);
-	else
+	else {
+		if (secure_computing(scno) == -1)
+			return -1;
 		audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0,
 				    regs->ARM_r1, regs->ARM_r2, regs->ARM_r3);
+	}
 
 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
 		return scno;
 	if (!(current->ptrace & PT_PTRACED))
 		return scno;
 
-	current_thread_info()->syscall = scno;
+	/*
+	 * IP is used to denote syscall entry/exit:
+	 * IP = 0 -> entry, =1 -> exit
+	 */
+	ip = regs->ARM_ip;
+	regs->ARM_ip = why;
 
 	/*
 	 * IP is used to denote syscall entry/exit: