linux-kernel - Re: Memory zeroed when made available to user process

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Message-ID: <20180627131248.GA3032@dhcp22.suse.cz>
Date:   Wed, 27 Jun 2018 15:12:48 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Richard Weinberger <richard.weinberger@...il.com>
Cc:     Jefferson Carpenter <jeffersoncarpenter2@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Memory zeroed when made available to user process

On Wed 27-06-18 13:29:05, Richard Weinberger wrote:
> On Wed, Jun 27, 2018 at 11:34 AM, Jefferson Carpenter
> <jeffersoncarpenter2@...il.com> wrote:
> > Is there a way for a user process to mark memory as 'sensitive' or
> > 'non-sensitive' when it is allocated?  That could allow it not to have to be
> > zeroed before being allocated to another process.
> 
> Isn't this what we have Meltdown and Spectre for? ;-)
> 
> No, memory from the kernel is always zeroed.
> libc offers malloc() and calloc() for this purpose.

Well, except for the weird MAP_UNINITIALIZED. Anyway agreed that this is
a bad idea and the flag should have never been merged. I've just
mentioned it for completness.

-- 
Michal Hocko
SUSE Labs