linux-kernel - RE: [PATCH] mm/vmalloc: randomize vmalloc() allocations

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Date:   Thu, 3 Dec 2020 23:15:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mike Rapoport' <rppt@...nel.org>,
        Topi Miettinen <toiwoton@...il.com>
CC:     "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Linux API <linux-api@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: RE: [PATCH] mm/vmalloc: randomize vmalloc() allocations

From: Mike Rapoport
> Sent: 03 December 2020 06:58
> 
> On Wed, Dec 02, 2020 at 08:49:06PM +0200, Topi Miettinen wrote:
> > On 1.12.2020 23.45, Topi Miettinen wrote:
> > > Memory mappings inside kernel allocated with vmalloc() are in
> > > predictable order and packed tightly toward the low addresses. With
> > > new kernel boot parameter 'randomize_vmalloc=1', the entire area is
> > > used randomly to make the allocations less predictable and harder to
> > > guess for attackers.

Isn't that going to horribly fragment the available address space
and make even moderate sized allocation requests fail (or sleep).

I'm not even sure that you need to use 'best fit' rather than
'first fit'.
'best fit' is certainly a lot better for a simple linked list
user space malloc.

	David

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