[PATCH 3.13 176/198] x86_32, entry: Do syscall exit work on badsys (CVE-2014-4508)

From: Kamal Mostafa
Date: Tue Jul 15 2014 - 18:02:41 EST -stable review patch. If anyone has any objections, please let me know.


From: Andy Lutomirski <luto@xxxxxxxxxxxxxx>

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@xxxxxxxxxx>
Reported-by: Toralf FÃrster <toralf.foerster@xxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/e09c499eade6fc321266dd6b54da7beb28d6991c.1403558229.git.luto@xxxxxxxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
arch/x86/kernel/entry_32.S | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 2780b8f..6491353 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -431,9 +431,10 @@ sysenter_past_esp:
jnz sysenter_audit
cmpl $(NR_syscalls), %eax
- jae syscall_badsys
+ jae sysenter_badsys
call *sys_call_table(,%eax,4)
movl %eax,PT_EAX(%esp)
@@ -683,7 +684,12 @@ END(syscall_fault)

movl $-ENOSYS,PT_EAX(%esp)
- jmp resume_userspace
+ jmp syscall_exit
+ movl $-ENOSYS,PT_EAX(%esp)
+ jmp sysenter_after_call

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