linux-kernel - Re: [PATCH v8 4/9] mm: introduce memfd_secret system call to create "secret" memory areas

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Date:   Sun, 15 Nov 2020 10:45:39 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Matthew Wilcox <willy@...radead.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>, Ingo Molnar <mingo@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        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, Hagen Paul Pfeifer <hagen@...u.net>
Subject: Re: [PATCH v8 4/9] mm: introduce memfd_secret system call to create
 "secret" memory areas

On Fri, Nov 13, 2020 at 02:06:56PM +0000, Matthew Wilcox wrote:
> On Tue, Nov 10, 2020 at 05:14:39PM +0200, Mike Rapoport wrote:
> > diff --git a/mm/Kconfig b/mm/Kconfig
> > index c89c5444924b..d8d170fa5210 100644
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -884,4 +884,7 @@ config ARCH_HAS_HUGEPD
> >  config MAPPING_DIRTY_HELPERS
> >          bool
> >  
> > +config SECRETMEM
> > +	def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
> 
> So I now have to build this in, whether I want it or not?

Why wouldn't anybody want this nice feature? ;-)

Now, seriously, I hesitated a lot about having a prompt here, but in the
end I've decided to go without it.

The added footprint is not so big, with x86 defconfig it's less than 8K
and with distro (I've checked with Fedora) config the difference is less
than 1k because they anyway have CMA=y.

As this is "security" feature, disros most probably would have this
enabled anyway, and I believe users that will see something like "Allow
hiding memory from the kernel" will hit Y there.

-- 
Sincerely yours,
Mike.