ARM: 7578/1: arch/move secure_computing into trace

There is very little difference in the TIF_SECCOMP and TIF_SYSCALL_WORK
path in entry-common.S, so merge TIF_SECCOMP into TIF_SYSCALL_WORK and
move seccomp into the syscall_trace_enter() handler.

Expanded some of the tracehook logic into the callers to make this code
more readable. Since tracehook needs to do register changing, this portion
is best left in its own function instead of copy/pasting into the callers.

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

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Will Drewry <wad@chromium.org>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

3 files changed, 24 insertions, 22 deletions

diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 8477b4c1d39f..cddda1f41f0f 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -151,10 +151,10 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *,
 #define TIF_SYSCALL_TRACE       8
 #define TIF_SYSCALL_AUDIT       9
 #define TIF_SYSCALL_TRACEPOINT  10
+#define TIF_SECCOMP             11      /* seccomp syscall filtering active */
 #define TIF_USING_IWMMXT        17
 #define TIF_MEMDIE              18      /* is terminating due to OOM killer */
 #define TIF_RESTORE_SIGMASK     20
-#define TIF_SECCOMP             21
 #define TIF_SWITCH_MM           22      /* deferred switch_mm */
 
 #define _TIF_SIGPENDING         (1 << TIF_SIGPENDING)
@@ -163,11 +163,12 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *,
 #define _TIF_SYSCALL_TRACE      (1 << TIF_SYSCALL_TRACE)
 #define _TIF_SYSCALL_AUDIT      (1 << TIF_SYSCALL_AUDIT)
 #define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
-#define _TIF_USING_IWMMXT       (1 << TIF_USING_IWMMXT)
 #define _TIF_SECCOMP            (1 << TIF_SECCOMP)
+#define _TIF_USING_IWMMXT       (1 << TIF_USING_IWMMXT)
 
 /* Checks for any syscall work in entry-common.S */
-#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SYSCALL_TRACEPOINT)
+#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
+                           _TIF_SYSCALL_TRACEPOINT | _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 417bac1846bd..b621871dd277 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -417,16 +417,6 @@ local_restart:
         ldr     r10, [tsk, #TI_FLAGS]           @ check for syscall tracing
         stmdb   sp!, {r4, r5}                   @ push fifth and sixth args
 
-#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_WORK         @ are we tracing syscalls?
         bne     __sys_trace
 
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 739db3a1b2d2..518536d93fba 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -916,16 +916,11 @@ enum ptrace_syscall_dir {
         PTRACE_SYSCALL_EXIT,
 };
 
-static int ptrace_syscall_trace(struct pt_regs *regs, int scno,
-                                enum ptrace_syscall_dir dir)
+static int tracehook_report_syscall(struct pt_regs *regs,
+                                    enum ptrace_syscall_dir dir)
 {
         unsigned long ip;
 
-        current_thread_info()->syscall = scno;
-
-        if (!test_thread_flag(TIF_SYSCALL_TRACE))
-                return scno;
-
         /*
          * IP is used to denote syscall entry/exit:
          * IP = 0 -> entry, =1 -> exit
@@ -944,19 +939,35 @@ static int ptrace_syscall_trace(struct pt_regs *regs, int scno,
 
 asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
 {
-        scno = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_ENTER);
+        current_thread_info()->syscall = scno;
+
+        /* Do the secure computing check first; failures should be fast. */
+        if (secure_computing(scno) == -1)
+                return -1;
+
+        if (test_thread_flag(TIF_SYSCALL_TRACE))
+                scno = tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
+
         if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
                 trace_sys_enter(regs, scno);
+
         audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1,
                             regs->ARM_r2, regs->ARM_r3);
+
         return scno;
 }
 
 asmlinkage int syscall_trace_exit(struct pt_regs *regs, int scno)
 {
-        scno = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_EXIT);
+        current_thread_info()->syscall = scno;
+
+        if (test_thread_flag(TIF_SYSCALL_TRACE))
+                scno = tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
+
         if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
                 trace_sys_exit(regs, scno);
+
         audit_syscall_exit(regs);
+
         return scno;
 }