linux-kernel - Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write

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Message-ID: <CA+DvKQKc8uq=1O5d41GRU6u=GkOvuCJzkbPPBcp2ohHLU7A25g@mail.gmail.com>
Date:   Sat, 8 Apr 2017 00:21:48 -0400
From:   Daniel Micay <danielmicay@...il.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Mathias Krause <minipli@...glemail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Mark Rutland <mark.rutland@....com>,
        Hoeun Ryu <hoeun.ryu@...il.com>,
        PaX Team <pageexec@...email.hu>,
        Emese Revfy <re.emese@...il.com>,
        Russell King <linux@...linux.org.uk>, X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap()

>> Fair enough. However, placing a BUG_ON(!(read_cr0() & X86_CR0_WP))
>> somewhere sensible should make those "leaks" visible fast -- and their
>> exploitation impossible, i.e. fail hard.
>
> The leaks surely exist and now we'll just add an exploitable BUG.

That didn't seem to matter for landing a rewrite of KSTACKOVERFLOW
with a bunch of *known* DoS bugs dealt with in grsecurity and those
were known issues that were unfixed for no apparent reason other than
keeping egos intact. It looks like there are still some left...

In that case, there also wasn't a security/performance advantage.