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Date:   Tue, 6 Oct 2020 01:44:14 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Jann Horn <jannh@google.com>
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Subject: Re: [PATCH RFC v2 0/6] Break heap spraying needed for exploiting
 use-after-free
Message-ID: <20201006004414.GP20115@casper.infradead.org>
References: <20200929183513.380760-1-alex.popov@linux.com>
 <91d564a6-9000-b4c5-15fd-8774b06f5ab0@linux.com>
 <CAG48ez1tNU_7n8qtnxTYZ5qt-upJ81Fcb0P2rZe38ARK=iyBkA@mail.gmail.com>
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On Tue, Oct 06, 2020 at 12:56:33AM +0200, Jann Horn wrote:
> It seems to me like, if you want to make UAF exploitation harder at
> the heap allocator layer, you could do somewhat more effective things
> with a probably much smaller performance budget. Things like
> preventing the reallocation of virtual kernel addresses with different
> types, such that an attacker can only replace a UAF object with
> another object of the same type. (That is not an idea I like very much
> either, but I would like it more than this proposal.) (E.g. some
> browsers implement things along those lines, I believe.)

The slab allocator already has that functionality.  We call it
TYPESAFE_BY_RCU, but if forcing that on by default would enhance security
by a measurable amount, it wouldn't be a terribly hard sell ...