linux-hardening - Re: [PATCH v4] mm: Optional full ASLR for mmap() and mremap()

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Date:   Tue, 17 Nov 2020 16:54:55 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Topi Miettinen <toiwoton@...il.com>
Cc:     linux-hardening@...r.kernel.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH v4] mm: Optional full ASLR for mmap() and mremap()

On Mon, Oct 26, 2020 at 06:05:18PM +0200, Topi Miettinen wrote:
> Writing a new value of 3 to /proc/sys/kernel/randomize_va_space
> enables full randomization of memory mappings created with mmap(NULL,
> ...). With 2, the base of the VMA used for such mappings is random,
> but the mappings are created in predictable places within the VMA and
> in sequential order. With 3, new VMAs are created to fully randomize
> the mappings. Also mremap(..., MREMAP_MAYMOVE) will move the mappings
> even if not necessary.

Is this worth it?

https://www.ndss-symposium.org/ndss2017/ndss-2017-programme/aslrcache-practical-cache-attacks-mmu/