linux-kernel - [PATCH 3.12 176/181] x86_32, entry: Do syscall exit work on badsys (CVE-2014-4508)

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Message-Id: <3ee8c4d6a43494d84ec3b0cae7e6e26bc312f8d6.1404128998.git.jslaby@suse.cz>
Date:	Mon, 30 Jun 2014 13:53:17 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Roland McGrath <roland@...hat.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 176/181] x86_32, entry: Do syscall exit work on badsys (CVE-2014-4508)

From: Andy Lutomirski <luto@...capital.net>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@...hat.com>
Reported-by: Toralf Förster <toralf.foerster@....de>
Signed-off-by: Andy Lutomirski <luto@...capital.net>
Link: http://lkml.kernel.org/r/e09c499eade6fc321266dd6b54da7beb28d6991c.1403558229.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 cef8f5132b87..3308125c90aa 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -434,9 +434,10 @@ 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
@@ -686,7 +687,12 @@ 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
 /*
-- 
2.0.0

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