linux-kernel - Re: [PATCH v3 01/23] x86/elf: Check in_x32_syscall() in compat_arch_setup_additional

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Message-ID: <87tulth9j8.ffs@nanos.tec.linutronix.de>
Date:   Sat, 19 Jun 2021 22:41:31 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Guo Ren <guoren@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will@...nel.org>, x86@...nel.org
Subject: Re: [PATCH v3 01/23] x86/elf: Check in_x32_syscall() in compat_arch_setup_additional_pages()

On Fri, Jun 11 2021 at 19:02, Dmitry Safonov wrote:
> Partly revert commit 3316ec8ccd34 ("x86/elf: Use e_machine to check for
> x32/ia32 in setup_additional_pages()") and commit 9a29a671902c ("elf:
> Expose ELF header on arch_setup_additional_pages()".
> Both patches did a good thing: removed usage of TIF_X32, but with
> a price of additional macros ARCH_SETUP_ADDITIONAL_PAGES() and ifdeffs.
>
> Instead, use in_x32_syscall() - the first thing load_elf_binary() does
> after parsing and checking new ELF binary. It's done that early after
> exec() that mmap() code already uses it straight away, which is needed
> to know which mmap_base to use (see arch_pick_mmap_layout()).
> Add comments to describe how it works.

I still have no idea what this is trying to solve. All you describe is
what this does.

Thanks,

        tglx