From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756011AbaGVRCT (ORCPT ); Tue, 22 Jul 2014 13:02:19 -0400 Received: from terminus.zytor.com ([198.137.202.10]:57541 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752620AbaGVRCR (ORCPT ); Tue, 22 Jul 2014 13:02:17 -0400 Date: Tue, 22 Jul 2014 10:01:23 -0700 From: tip-bot for Sven Wegener Message-ID: Cc: luto@amacapital.net, linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, sven.wegener@stealer.net, tglx@linutronix.de Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, luto@amacapital.net, sven.wegener@stealer.net, tglx@linutronix.de In-Reply-To: References: To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86_32, entry: Store badsys error code in %eax Git-Commit-ID: 8142b215501f8b291a108a202b3a053a265b03dd X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 8142b215501f8b291a108a202b3a053a265b03dd Gitweb: http://git.kernel.org/tip/8142b215501f8b291a108a202b3a053a265b03dd Author: Sven Wegener AuthorDate: Tue, 22 Jul 2014 10:26:06 +0200 Committer: H. Peter Anvin CommitDate: Tue, 22 Jul 2014 02:34:05 -0700 x86_32, entry: Store badsys error code in %eax 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: # If 554086d is backported Signed-off-by: H. Peter Anvin --- 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 dbaa23e..0d0c9d4 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -425,8 +425,8 @@ 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 @@ -502,6 +502,7 @@ 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 @@ -675,12 +676,12 @@ 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