linux-kernel - Re: [PATCH v19 6/8] PM: hibernate: disable when there are active secretmem users

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Date:   Tue, 18 May 2021 18:32:29 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Hagen Paul Pfeifer <hagen@...u.net>,
        Ingo Molnar <mingo@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        Yury Norov <yury.norov@...il.com>, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org
Subject: Re: [PATCH v19 6/8] PM: hibernate: disable when there are active
 secretmem users

On Tue, 2021-05-18 at 11:24 +0100, Mark Rutland wrote:
> On Thu, May 13, 2021 at 09:47:32PM +0300, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@...ux.ibm.com>
> > 
> > It is unsafe to allow saving of secretmem areas to the hibernation
> > snapshot as they would be visible after the resume and this
> > essentially will defeat the purpose of secret memory mappings.
> > 
> > Prevent hibernation whenever there are active secret memory users.
> 
> Have we thought about how this is going to work in practice, e.g. on
> mobile systems? It seems to me that there are a variety of common
> applications which might want to use this which people don't expect
> to inhibit hibernate (e.g. authentication agents, web browsers).

If mobile systems require hibernate, then the choice is to disable this
functionality or implement a secure hibernation store.   I also thought
most mobile hibernation was basically equivalent to S3, in which case
there's no actual writing of ram into storage, in which case there's no
security barrier and likely the inhibition needs to be made a bit more
specific to the suspend to disk case?

> Are we happy to say that any userspace application can incidentally
> inhibit hibernate?

Well, yes, for the laptop use case because we don't want suspend to
disk to be able to compromise the secret area.  You can disable this
for mobile if you like, or work out how to implement hibernate securely
if you're really suspending to disk.

James