From patchwork Thu Sep 3 05:48:07 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "dalias@libc.org" X-Patchwork-Id: 11752429 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 90E4D138A for ; Thu, 3 Sep 2020 05:48:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83F3220665 for ; Thu, 3 Sep 2020 05:48:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726263AbgICFsI (ORCPT ); Thu, 3 Sep 2020 01:48:08 -0400 Received: from brightrain.aerifal.cx ([216.12.86.13]:49122 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725919AbgICFsH (ORCPT ); Thu, 3 Sep 2020 01:48:07 -0400 Date: Thu, 3 Sep 2020 01:48:07 -0400 From: Rich Felker To: linux-sh@vger.kernel.org Cc: John Paul Adrian Glaubitz , Michael Karcher , linux-kernel@vger.kernel.org, Yoshinori Sato Subject: [PATCH] sh: fix syscall tracing Message-ID: <20200903054803.GX3265@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-sh-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org Addition of SECCOMP_FILTER exposed a longstanding bug in do_syscall_trace_enter, whereby r0 (the 5th argument register) was mistakenly used where r3 (syscall_nr) was intended. By overwriting r0 rather than r3 with -1 when attempting to block a syscall, the existing code would instead have caused the syscall to execute with an argument clobbered. Commit 0bb605c2c7f2b4b3 then introduced skipping of the syscall when do_syscall_trace_enter returns -1, so that the return value set by seccomp filters would not be clobbered by -ENOSYS. This eliminated the clobbering of the 5th argument register, but instead caused syscalls made with a 5th argument of -1 to be misinterpreted as a request by do_syscall_trace_enter to suppress the syscall. Fixes: 0bb605c2c7f2b4b3 ("sh: Add SECCOMP_FILTER") Fixes: ab99c733ae73cce3 ("sh: Make syscall tracer use tracehook notifiers, add TIF_NOTIFY_RESUME.") Signed-off-by: Rich Felker Tested-by: John Paul Adrian Glaubitz --- arch/sh/kernel/entry-common.S | 1 - arch/sh/kernel/ptrace_32.c | 15 +++++---------- 2 files changed, 5 insertions(+), 11 deletions(-) diff --git a/arch/sh/kernel/entry-common.S b/arch/sh/kernel/entry-common.S index ad963104d22d..91ab2607a1ff 100644 --- a/arch/sh/kernel/entry-common.S +++ b/arch/sh/kernel/entry-common.S @@ -370,7 +370,6 @@ syscall_trace_entry: nop cmp/eq #-1, r0 bt syscall_exit - mov.l r0, @(OFF_R0,r15) ! Save return value ! Reload R0-R4 from kernel stack, where the ! parent may have modified them using ! ptrace(POKEUSR). (Note that R0-R2 are diff --git a/arch/sh/kernel/ptrace_32.c b/arch/sh/kernel/ptrace_32.c index b05bf92f9c32..5281685f6ad1 100644 --- a/arch/sh/kernel/ptrace_32.c +++ b/arch/sh/kernel/ptrace_32.c @@ -455,16 +455,11 @@ long arch_ptrace(struct task_struct *child, long request, asmlinkage long do_syscall_trace_enter(struct pt_regs *regs) { - long ret = 0; - if (test_thread_flag(TIF_SYSCALL_TRACE) && - tracehook_report_syscall_entry(regs)) - /* - * Tracing decided this syscall should not happen. - * We'll return a bogus call number to get an ENOSYS - * error, but leave the original number in regs->regs[0]. - */ - ret = -1L; + tracehook_report_syscall_entry(regs)) { + regs->regs[0] = -ENOSYS; + return -1; + } if (secure_computing() == -1) return -1; @@ -475,7 +470,7 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs *regs) audit_syscall_entry(regs->regs[3], regs->regs[4], regs->regs[5], regs->regs[6], regs->regs[7]); - return ret ?: regs->regs[0]; + return 0; } asmlinkage void do_syscall_trace_leave(struct pt_regs *regs)