linux-kernel - Re: [PATCH v16 1/5] mm: add VM_DROPPABLE for designating always lazily freeable mappings

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Message-ID: <CALCETrVJFefyDT6U3QoHdZvNh=3nqk=3AK88eRuqdn4W4t8vsA@mail.gmail.com>
Date: Fri, 7 Jun 2024 11:40:33 -0700
From: Andy Lutomirski <luto@...capital.net>
To: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: linux-kernel@...r.kernel.org, patches@...ts.linux.dev, tglx@...utronix.de, 
	linux-crypto@...r.kernel.org, linux-api@...r.kernel.org, x86@...nel.org, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>, "Carlos O'Donell" <carlos@...hat.com>, 
	Florian Weimer <fweimer@...hat.com>, Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>, 
	Christian Brauner <brauner@...nel.org>, David Hildenbrand <dhildenb@...hat.com>, linux-mm@...ck.org
Subject: Re: [PATCH v16 1/5] mm: add VM_DROPPABLE for designating always
 lazily freeable mappings

On Tue, May 28, 2024 at 5:24 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> The vDSO getrandom() implementation works with a buffer allocated with a
> new system call that has certain requirements:
>
> - It shouldn't be written to core dumps.
>   * Easy: VM_DONTDUMP.

I'll bite: why shouldn't it be written to core dumps?

The implementation is supposed to be forward-secret: an attacker who
gets the state can't predict prior outputs.  And a core-dumped process
is dead: there won't be future outputs.