linux-kernel - non-x86 per-task stack canaries

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Message-ID: <CAGXu5jLCAdPOKZFotaWZ8MjwqW8Eq9_tLc_fgbYsTcbVWv77AQ@mail.gmail.com>
Date:   Mon, 26 Jun 2017 14:04:01 -0700
From:   Kees Cook <keescook@...gle.com>
To:     "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: non-x86 per-task stack canaries

Hi,

The stack protector functionality on x86_64 uses %gs:0x28 (%gs is the
percpu area) for __stack_chk_guard, and all other architectures use a
global variable instead. This means we never change the stack canary
on non-x86 architectures which allows for a leak in one task to expose
the canary in another task.

I'm curious what thoughts people may have about how to get this
correctly implemented. Teaching the compiler about per-cpu data sounds
exciting. :)

-Kees

-- 
Kees Cook
Pixel Security