linux-kernel - Re: [RFC PATCH 1/5] mm: intorduce __GFP_UNMAPPED and unmapped

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZGbPz109t9Huxrqy@moria.home.lan>
Date:   Thu, 18 May 2023 21:24:31 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Song Liu <song@...nel.org>
Cc:     Mike Rapoport <rppt@...nel.org>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [RFC PATCH 1/5] mm: intorduce __GFP_UNMAPPED and unmapped_alloc()

On Thu, May 18, 2023 at 01:51:08PM -0700, Song Liu wrote:
 
> To allocate memory for text, we will allocate 2MiB, make it ROX, and then
> use it for many small allocations. IIUC, buddy allocator will use unallocated
> parts of this page for metadata. I guess this may be a problem, as the
> whole page is ROX now, and we have to use text_poke to write to it.

The standard kernel buddy allocator does _not_ store anything in the
page itself - because the page might be a highmem page.

That's also why I went with the bitmap for my slab allocator; standard
kernel slab allocator stores a freelist ptr in free objects.