From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753611AbbHMQpU (ORCPT ); Thu, 13 Aug 2015 12:45:20 -0400 Received: from mail-oi0-f46.google.com ([209.85.218.46]:36551 "EHLO mail-oi0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752210AbbHMQpR (ORCPT ); Thu, 13 Aug 2015 12:45:17 -0400 MIME-Version: 1.0 In-Reply-To: References: <55CA90B4.2010205@list.ru> From: Andy Lutomirski Date: Thu, 13 Aug 2015 09:44:56 -0700 Message-ID: Subject: Re: [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu To: Linus Torvalds Cc: Stas Sergeev , Linux kernel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 13, 2015 at 9:43 AM, Linus Torvalds wrote: > On Thu, Aug 13, 2015 at 9:34 AM, Linus Torvalds > wrote: >> >> Are you sure? From the description by Stas, the problem is literally >> the *restoring* action of the sigcontext, and trying to restore a SS >> value that is no longer valid. >> >> "The crash happens when DOS program terminates. >> At that point dosemu subverts the execution flow by >> replacing segregs and cs/ip ss/sp in sigcontext with its own. >> But __pad0 still has DOS SS, which crash because (presumably) >> the DOS LDT have been just removed" > > Side note: if this is the main issue, and the problem is the "iret" > faulting when trying to restore SS (and causing an unexpected SIGSEGV > that dosemu crashes on), then an alternate model might be to keep the > save/restore SS code, but do a "VERW" on the SS descriptor in > restore_sigcontext(), and silently just replacing it with __USER_DS if > that fails. > I have a patch to do approximately that (using LAR instead of VERW to rule out DPL < 3. I'm 90% sure that the regs->ss = __USER_DS thing is a problem. Read farther up in the thread. I'm leaning toward saying we should revert, cc: stable, and fix it better for 4.3. --Andy