From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751264AbaKPWA3 (ORCPT ); Sun, 16 Nov 2014 17:00:29 -0500 Received: from 1wt.eu ([62.212.114.60]:47850 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750764AbaKPWA1 (ORCPT ); Sun, 16 Nov 2014 17:00:27 -0500 Message-Id: <20141116215328.734899238@1wt.eu> User-Agent: quilt/0.48-1 Date: Sun, 16 Nov 2014 22:53:30 +0100 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Sven Wegener , "H. Peter Anvin" , Willy Tarreau Subject: [ 02/48] x86_32, entry: Store badsys error code in %eax In-Reply-To: <28c765bc23bd4bae1611534e510f49f8@local> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Sven Wegener Commit 554086d ("x86_32, entry: Do syscall exit work on badsys (CVE-2014-4508)") introduced a regression in the x86_32 syscall entry code, resulting in syscall() not returning proper errors for undefined syscalls on CPUs supporting the sysenter feature. The following code: > int result = syscall(666); > printf("result=%d errno=%d error=%s\n", result, errno, strerror(errno)); results in: > result=666 errno=0 error=Success Obviously, the syscall return value is the called syscall number, but it should have been an ENOSYS error. When run under ptrace it behaves correctly, which makes it hard to debug in the wild: > result=-1 errno=38 error=Function not implemented The %eax register is the return value register. For debugging via ptrace the syscall entry code stores the complete register context on the stack. The badsys handlers only store the ENOSYS error code in the ptrace register set and do not set %eax like a regular syscall handler would. The old resume_userspace call chain contains code that clobbers %eax and it restores %eax from the ptrace registers afterwards. The same goes for the ptrace-enabled call chain. When ptrace is not used, the syscall return value is the passed-in syscall number from the untouched %eax register. Use %eax as the return value register in syscall_badsys and sysenter_badsys, like a real syscall handler does, and have the caller push the value onto the stack for ptrace access. Signed-off-by: Sven Wegener Link: http://lkml.kernel.org/r/alpine.LNX.2.11.1407221022380.31021@titan.int.lan.stealer.net Reviewed-and-tested-by: Andy Lutomirski Cc: Signed-off-by: H. Peter Anvin (cherry picked from commit 8142b215501f8b291a108a202b3a053a265b03dd) Signed-off-by: Willy Tarreau --- arch/x86/kernel/entry_32.S | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index 40a0d02..3188ca4 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -447,8 +447,8 @@ sysenter_do_call: cmpl $(nr_syscalls), %eax jae sysenter_badsys call *sys_call_table(,%eax,4) - movl %eax,PT_EAX(%esp) sysenter_after_call: + movl %eax,PT_EAX(%esp) LOCKDEP_SYS_EXIT DISABLE_INTERRUPTS(CLBR_ANY) TRACE_IRQS_OFF @@ -528,6 +528,7 @@ ENTRY(system_call) jae syscall_badsys syscall_call: call *sys_call_table(,%eax,4) +syscall_after_call: movl %eax,PT_EAX(%esp) # store the return value syscall_exit: LOCKDEP_SYS_EXIT @@ -702,12 +703,12 @@ syscall_fault: END(syscall_fault) syscall_badsys: - movl $-ENOSYS,PT_EAX(%esp) - jmp syscall_exit + movl $-ENOSYS,%eax + jmp syscall_after_call END(syscall_badsys) sysenter_badsys: - movl $-ENOSYS,PT_EAX(%esp) + movl $-ENOSYS,%eax jmp sysenter_after_call END(syscall_badsys) CFI_ENDPROC -- 1.7.12.2.21.g234cd45.dirty