linux-kernel - Re: [RFC PATCH v2 04/10] lib: vdso: get pointer to vdso data from the arch

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrW9hsrVVzudvRY22AqakcsrVzqp=SdwOTwW2zRBK+kEaA@mail.gmail.com>
Date:   Mon, 23 Dec 2019 18:27:40 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrew Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        X86 ML <x86@...nel.org>
Subject: Re: [RFC PATCH v2 04/10] lib: vdso: get pointer to vdso data from the arch

On Mon, Dec 23, 2019 at 6:31 AM Christophe Leroy
<christophe.leroy@....fr> wrote:
>
> On powerpc, __arch_get_vdso_data() clobbers the link register,
> requiring the caller to set a stack frame in order to save it.
>
> As the parent function already has to set a stack frame and save
> the link register to call the C vdso function, retriving the
> vdso data pointer there is lighter.

I'm confused.  Can't you inline __arch_get_vdso_data()?  Or is the
issue that you can't retrieve the program counter on power without
clobbering the link register?

I would imagine that this patch generates worse code on any
architecture with PC-relative addressing modes (which includes at
least x86_64, and I would guess includes most modern architectures).

--Andy