From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78133C4727E for ; Thu, 1 Oct 2020 21:49:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 27D0D2075F for ; Thu, 1 Oct 2020 21:49:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601588984; bh=6/33owwRi5A7FNKzkkiUdJvvFMmIQNDCM+CvjlAcElY=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=J5yyeNwpL/a8Ge8E6XrP1o1mWf2G6X6tHGY61Cg5hvil0XqGKzs5ijCAr8EOsoAWf pCaVZ7NC8rYaSdtcoMoqrcx6twHEqYG3ZxA9hswMQFCFuVht2K3e5ewCN0VRbQVPIn QeAYQIX3ZqN7ayecQ8V59AbaDl6QJHS6qS8hOSHo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733103AbgJAVtm (ORCPT ); Thu, 1 Oct 2020 17:49:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:40072 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726626AbgJAVtm (ORCPT ); Thu, 1 Oct 2020 17:49:42 -0400 Received: from mail-wr1-f52.google.com (mail-wr1-f52.google.com [209.85.221.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E9D1A2177B for ; Thu, 1 Oct 2020 21:49:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601588982; bh=6/33owwRi5A7FNKzkkiUdJvvFMmIQNDCM+CvjlAcElY=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=BS+VwNksm+Izlsdnlf3ZUdWncUhsTErPQl10AGJ8FSyBAkLgqr6N1uAypC7PYP+f0 7d4VVLUHZ4gEfuc5g7ccLgjBM4Xk9jwBToFZOLN5cNI7B4PGRCczrNiHdlj6V8s1z8 gW6Y5OZWuEfob38snFMoaGjY1/08DnKhHPRj30iU= Received: by mail-wr1-f52.google.com with SMTP id j2so340700wrx.7 for ; Thu, 01 Oct 2020 14:49:41 -0700 (PDT) X-Gm-Message-State: AOAM5322M7d5N3ZU+YX8LcdvhB3v6lASemihrzWAQPLrPN3sz3ZhAq21 JEwuTH05J8kZA3EOpWrRmi+kGp5GnDS5M78q/zReRA== X-Google-Smtp-Source: ABdhPJy08zx7EFM9Zzjkij4vwZV7ukFXxeyn8MyPYxiVmJlaKl3n7NLOG2W/8E07JIknS49kmlp3xkwLg2/1M3bRJpg= X-Received: by 2002:adf:ce8e:: with SMTP id r14mr11100849wrn.257.1601588980460; Thu, 01 Oct 2020 14:49:40 -0700 (PDT) MIME-Version: 1.0 References: <20201001205819.27879-1-krisman@collabora.com> <20201001205819.27879-6-krisman@collabora.com> In-Reply-To: <20201001205819.27879-6-krisman@collabora.com> From: Andy Lutomirski Date: Thu, 1 Oct 2020 14:49:28 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 5/9] x86: elf: Use e_machine to select start_thread for x32 To: Gabriel Krisman Bertazi Cc: Andrew Lutomirski , Thomas Gleixner , Christoph Hellwig , "H. Peter Anvin" , Borislav Petkov , Robert Richter , Peter Zijlstra , Ingo Molnar , X86 ML , LKML , Dave Hansen , kernel@collabora.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 1, 2020 at 1:59 PM Gabriel Krisman Bertazi wrote: > > Since TIF_X32 is going away, avoid using it to find the ELF type on > compat_start_thread > > According to SysV AMD64 ABI Draft, an AMD64 ELF object using ILP32 must > have ELFCLASS32 with (E_MACHINE == EM_X86_64), so use that ELF field to > differentiate a x32 object from a IA32 object when executing > start_thread in compat mode. > > Signed-off-by: Gabriel Krisman Bertazi > --- > arch/x86/include/asm/elf.h | 11 +++++++++-- > arch/x86/kernel/process_64.c | 11 +++++++---- > 2 files changed, 16 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h > index 9220efc65d78..33c1c9be2e07 100644 > --- a/arch/x86/include/asm/elf.h > +++ b/arch/x86/include/asm/elf.h > @@ -186,8 +186,15 @@ static inline void elf_common_init(struct thread_struct *t, > #define COMPAT_ELF_PLAT_INIT(regs, load_addr) \ > elf_common_init(¤t->thread, regs, __USER_DS) > > -void compat_start_thread(struct pt_regs *regs, u32 new_ip, u32 new_sp); > -#define compat_start_thread compat_start_thread > +void compat_start_thread_ia32(struct pt_regs *regs, u32 new_ip, u32 new_sp); > +void compat_start_thread_x32(struct pt_regs *regs, u32 new_ip, u32 new_sp); > +#define compat_start_thread(regs, new_ip, new_sp) \ > +do { \ > + if (elf_ex->e_machine == EM_X86_64) \ > + compat_start_thread_x32(regs, new_ip, new_sp); \ > + else \ > + compat_start_thread_ia32(regs, new_ip, new_sp); \ > +} while (0) This is evil -- it looks like a real function, but it's not. Can you instead add a const struct elf32_hdr *elf_ex parameter to all the compat_start_thread implementations? There appear to be only four of them in the whole kernel. For patches like this, it should be fine to do it all as one patch as long as you Cc all the arch maintainers. --Andy