x86_32, entry: Do syscall exit work on badsys (CVE-2014-4508)

The bad syscall nr paths are their own incomprehensible route
through the entry control flow.  Rearrange them to work just like
syscalls that return -ENOSYS.

This fixes an OOPS in the audit code when fast-path auditing is
enabled and sysenter gets a bad syscall nr (CVE-2014-4508).

This has probably been broken since Linux 2.6.27:
af0575bba0 i386 syscall audit fast-path

Cc: stable@vger.kernel.org
Cc: Roland McGrath <roland@redhat.com>
Reported-by: Toralf Förster <toralf.foerster@gmx.de>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/e09c499eade6fc321266dd6b54da7beb28d6991c.1403558229.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index f0da82b8e634..dbaa23e78b36 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -423,9 +423,10 @@ sysenter_past_esp:
         jnz sysenter_audit
 sysenter_do_call:
         cmpl $(NR_syscalls), %eax
-        jae syscall_badsys
+        jae sysenter_badsys
         call *sys_call_table(,%eax,4)
         movl %eax,PT_EAX(%esp)
+sysenter_after_call:
         LOCKDEP_SYS_EXIT
         DISABLE_INTERRUPTS(CLBR_ANY)
         TRACE_IRQS_OFF
@@ -675,7 +676,12 @@ END(syscall_fault)
 
 syscall_badsys:
         movl $-ENOSYS,PT_EAX(%esp)
-        jmp resume_userspace
+        jmp syscall_exit
+END(syscall_badsys)
+
+sysenter_badsys:
+        movl $-ENOSYS,PT_EAX(%esp)
+        jmp sysenter_after_call
 END(syscall_badsys)
         CFI_ENDPROC