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Message-ID: <CAG48ez2R=Ov2Z9zn_W9+C3gHqOkPdQKAY=4SMWDUG=NfP=3eJw@mail.gmail.com>
Date: Mon, 5 Dec 2022 20:13:36 +0100
From: Jann Horn <jannh@...gle.com>
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>,
Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v11 1/4] random: add vgetrandom_alloc() syscall
On Mon, Dec 5, 2022 at 3:01 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
> + mm->def_flags |=
> + /*
> + * Don't allow state to be written to swap, to preserve forward secrecy.
> + * This works in conjunction with MAP_LOCKED in do_mmap(), below, which
> + * actually does the locking (and associated permission check and accounting).
> + * Here, VM_LOCKONFAULT together with VM_NORESERVE simply make the mlocking
> + * happen the first time it's actually used, the same as when calling
> + * mlock2(MLOCK_ONFAULT) from userspace.
> + */
> + VM_LOCKONFAULT | VM_NORESERVE |
Have you checked the interaction with this line in dup_mmap()?
"tmp->vm_flags &= ~(VM_LOCKED | VM_LOCKONFAULT);"
As the mlock.2 manpage says, "Memory locks are not inherited by a
child created via fork(2)". I think the intention here is that the VMA
should stay unswappable after fork(), right?
Of course, trying to reserve more mlocked memory in fork() would also
be problematic...
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