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Date: Wed, 26 Apr 2017 04:01:28 +0200
From: "PaX Team" <>
To:, Kees Cook <>
CC: Kees Cook <>, Peter Zijlstra <>,
        Jann Horn <>, Eric Biggers <>,
        Christoph Hellwig <>,
        "" <>,
        James Bottomley <>,
        Elena Reshetova <>,
        Hans Liljestrand <>,
        David Windsor <>, "" <>,
        Ingo Molnar <>, Arnd Bergmann <>,
        Greg Kroah-Hartman <>,
        "David S. Miller" <>,
        Rik van Riel <>,
        linux-arch <>,
        "" <>
Subject: Re: [PATCH v2 0/2] x86, refcount: Implement fast refcount overflow

On 25 Apr 2017 at 15:56, Kees Cook wrote:

> This protection is a modified version of the x86 PAX_REFCOUNT
> implementation from PaX/grsecurity. This speeds up the refcount_t API by
> duplicating the existing atomic_t implementation with a single instruction
> added to detect if the refcount has wrapped past INT_MAX (or below 0)
> resulting in a signed value.

'signed value' sounds somewhat ambiguous given that in C a signed type (such
as the one beneath refcount_t) can have both negative and positive values yet
you didn't mean the latter here i guess.

> Various differences from PaX:
> - uses "js" instead of "jo" to trap all signed results instead of just
>   under/overflow transitions

there're differences in my 4.11 port but this isn't one of them.

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