powerpc/kernel: Switch to using MAX_ERRNO

Currently on powerpc we have our own #define for the highest (negative)
errno value, called _LAST_ERRNO. This is defined to be 516, for reasons
which are not clear.

The generic code, and x86, use MAX_ERRNO, which is defined to be 4095.

In particular seccomp uses MAX_ERRNO to restrict the value that a
seccomp filter can return.

Currently with the mismatch between _LAST_ERRNO and MAX_ERRNO, a seccomp
tracer wanting to return 600, expecting it to be seen as an error, would
instead find on powerpc that userspace sees a successful syscall with a
return value of 600.

To avoid this inconsistency, switch powerpc to use MAX_ERRNO.

We are somewhat confident that generic syscalls that can return a
non-error value above negative MAX_ERRNO have already been updated to
use force_successful_syscall_return().

I have also checked all the powerpc specific syscalls, and believe that
none of them expect to return a non-error value between -MAX_ERRNO and
-516. So this change should be safe ...

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Kees Cook <keescook@chromium.org>

3 files changed, 5 insertions, 5 deletions

diff --git a/arch/powerpc/include/uapi/asm/errno.h b/arch/powerpc/include/uapi/asm/errno.h
index 8c145fd17d86..e8b6b5f7de7c 100644
--- a/arch/powerpc/include/uapi/asm/errno.h
+++ b/arch/powerpc/include/uapi/asm/errno.h
@@ -6,6 +6,4 @@
 #undef  EDEADLOCK
 #define EDEADLOCK       58      /* File locking deadlock error */
 
-#define _LAST_ERRNO     516
-
 #endif  /* _ASM_POWERPC_ERRNO_H */
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 46fc0f4d8982..67ecdf61f4e3 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -20,6 +20,7 @@
  */
 
 #include <linux/errno.h>
+#include <linux/err.h>
 #include <linux/sys.h>
 #include <linux/threads.h>
 #include <asm/reg.h>
@@ -354,7 +355,7 @@ ret_from_syscall:
         SYNC
         MTMSRD(r10)
         lwz     r9,TI_FLAGS(r12)
-        li      r8,-_LAST_ERRNO
+        li      r8,-MAX_ERRNO
         andi.   r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
         bne-    syscall_exit_work
         cmplw   0,r3,r8
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 579e0f9a2d57..ee15d3c62e26 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -19,6 +19,7 @@
  */
 
 #include <linux/errno.h>
+#include <linux/err.h>
 #include <asm/unistd.h>
 #include <asm/processor.h>
 #include <asm/page.h>
@@ -207,7 +208,7 @@ system_call:			/* label this so stack traces look sane */
 #endif /* CONFIG_PPC_BOOK3E */
 
         ld      r9,TI_FLAGS(r12)
-        li      r11,-_LAST_ERRNO
+        li      r11,-MAX_ERRNO
         andi.   r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
         bne-    syscall_exit_work
         cmpld   r3,r11
@@ -277,7 +278,7 @@ syscall_exit_work:
         beq+    0f
         REST_NVGPRS(r1)
         b       2f
-0:      cmpld   r3,r11          /* r10 is -LAST_ERRNO */
+0:      cmpld   r3,r11          /* r11 is -MAX_ERRNO */
         blt+    1f
         andi.   r0,r9,_TIF_NOERROR
         bne-    1f