From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from vmicros1.altlinux.org ([194.107.17.57]:51620 "EHLO vmicros1.altlinux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726037AbgFBSG6 (ORCPT ); Tue, 2 Jun 2020 14:06:58 -0400 Date: Tue, 2 Jun 2020 21:00:51 +0300 From: "Dmitry V. Levin" Subject: [PATCH] s390: fix syscall_get_error for compat processes Message-ID: <20200602180051.GA2427@altlinux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-s390-owner@vger.kernel.org List-ID: To: Heiko Carstens , Vasily Gorbik , Christian Borntraeger Cc: Elvira Khabirova , Eugene Syromyatnikov , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org If both the tracer and the tracee are compat processes, and gprs[2] is assigned a value by __poke_user_compat, then the higher 32 bits of gprs[2] are cleared, IS_ERR_VALUE() always returns false, and syscall_get_error() always returns 0. Fix the implementation by sign-extending the value for compat processes the same way as x86 implementation does. The bug was exposed to user space by commit 201766a20e30f ("ptrace: add PTRACE_GET_SYSCALL_INFO request") and detected by strace test suite. This change fixes strace syscall tampering on s390. Fixes: 753c4dd6a2fa2 ("[S390] ptrace changes") Cc: Elvira Khabirova Cc: stable@vger.kernel.org # v2.6.28+ Signed-off-by: Dmitry V. Levin --- arch/s390/include/asm/syscall.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h index f073292e9fdb..c07633824715 100644 --- a/arch/s390/include/asm/syscall.h +++ b/arch/s390/include/asm/syscall.h @@ -33,7 +33,17 @@ static inline void syscall_rollback(struct task_struct *task, static inline long syscall_get_error(struct task_struct *task, struct pt_regs *regs) { - return IS_ERR_VALUE(regs->gprs[2]) ? regs->gprs[2] : 0; + unsigned long error = regs->gprs[2]; +#ifdef CONFIG_COMPAT + if (test_tsk_thread_flag(task, TIF_31BIT)) { + /* + * Sign-extend the value so (int)-EFOO becomes (long)-EFOO + * and will match correctly in comparisons. + */ + error = (long) (int) error; + } +#endif + return IS_ERR_VALUE(error) ? error : 0; } static inline long syscall_get_return_value(struct task_struct *task, -- ldv