linux-kernel - Re: [PATCH v1 1/4] syscalls: Restore address limit after a syscall

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Date:   Wed, 8 Mar 2017 21:58:15 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Thomas Garnier <thgarnie@...gle.com>
Cc:     Arnd Bergmann <arnd@...db.de>, David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dave Hansen <dave.hansen@...el.com>,
        René Nyffenegger <mail@...enyffenegger.ch>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Petr Mladek <pmladek@...e.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Helge Deller <deller@....de>, Rik van Riel <riel@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>,
        Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Brian Gerst <brgerst@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Jan Beulich <JBeulich@...e.com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Laura Abbott <labbott@...hat.com>,
        Andre Przywara <andre.przywara@....com>,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v1 1/4] syscalls: Restore address limit after a syscall

On Wed, Mar 08, 2017 at 01:38:41PM -0800, Thomas Garnier wrote:
> This patch prevents a syscall to modify the address limit of the
> caller. The address limit is kept by the syscall wrapper and restored
> just after the syscall ends.

I would much rather architectures were given the opportunity to code up
checks like this efficiently (iow, inline in the exit path assembly),
rather than having to unconditionally call an additional function on
every syscall, with its register saving overheads.

-- 
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