linux-kernel - Re: [patch 2/3] x86/vdso: Plug race between mapping and ELF header setup

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Message-ID: <CALCETrWfdOn0nyYYghmDydu1ZcfV0ZFgwp3VCV4HtHJHJBP3pg@mail.gmail.com>
Date:   Mon, 10 Apr 2017 08:56:06 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mathias Krause <minipli@...glemail.com>,
        stable <stable@...r.kernel.org>
Subject: Re: [patch 2/3] x86/vdso: Plug race between mapping and ELF header setup

On Mon, Apr 10, 2017 at 8:14 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> The vsyscall32 sysctl can racy against a concurrent fork when it switches
> from disabled to enabled:
>
>     arch_setup_additional_pages()
>         if (vdso32_enabled)
>            --> No mapping
>                                         sysctl.vsysscall32()
>                                           --> vdso32_enabled = true
>     create_elf_tables()
>       ARCH_DLINFO_IA32
>         if (vdso32_enabled) {
>            --> Add VDSO entry with NULL pointer
>
> Make ARCH_DLINFO_IA32 check whether the VDSO mapping has been set up for
> the newly forked process or not.

Acked-by: Andy Lutomirski <luto@...nel.org>