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

commit 554086d85e71f30abe46fc014fea31929a7c6a8a upstream.

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: 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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index d2d488b..db090f6 100644 (file)
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -427,9 +427,10 @@ 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
@@ -681,7 +682,12 @@ 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
 /*