linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Michal Hocko <mhocko@suse.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Borislav Petkov <bp@alien8.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christopher Lameter <cl@linux.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	David Hildenbrand <david@redhat.com>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	James Bottomley <jejb@linux.ibm.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Matthew Wilcox <willy@infradead.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>,
	Shuah Khan <shuah@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
	linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org,
	x86@kernel.org, Hagen Paul Pfeifer <hagen@jauu.net>,
	Palmer Dabbelt <palmerdabbelt@google.com>
Subject: Re: [PATCH v16 06/11] mm: introduce memfd_secret system call to create "secret" memory areas
Date: Tue, 26 Jan 2021 10:20:23 +0100	[thread overview]
Message-ID: <20210126092023.GH827@dhcp22.suse.cz> (raw)
In-Reply-To: <20210126090013.GF827@dhcp22.suse.cz>

On Tue 26-01-21 10:00:14, Michal Hocko wrote:
> On Tue 26-01-21 10:33:11, Mike Rapoport wrote:
> > On Tue, Jan 26, 2021 at 08:16:14AM +0100, Michal Hocko wrote:
> > > On Mon 25-01-21 23:36:18, Mike Rapoport wrote:
> > > > On Mon, Jan 25, 2021 at 06:01:22PM +0100, Michal Hocko wrote:
> > > > > On Thu 21-01-21 14:27:18, Mike Rapoport wrote:
> > > > > > From: Mike Rapoport <rppt@linux.ibm.com>
> > > > > > 
> > > > > > Introduce "memfd_secret" system call with the ability to create memory
> > > > > > areas visible only in the context of the owning process and not mapped not
> > > > > > only to other processes but in the kernel page tables as well.
> > > > > > 
> > > > > > The user will create a file descriptor using the memfd_secret() system
> > > > > > call. The memory areas created by mmap() calls from this file descriptor
> > > > > > will be unmapped from the kernel direct map and they will be only mapped in
> > > > > > the page table of the owning mm.
> > > > > > 
> > > > > > The secret memory remains accessible in the process context using uaccess
> > > > > > primitives, but it is not accessible using direct/linear map addresses.
> > > > > > 
> > > > > > Functions in the follow_page()/get_user_page() family will refuse to return
> > > > > > a page that belongs to the secret memory area.
> > > > > > 
> > > > > > A page that was a part of the secret memory area is cleared when it is
> > > > > > freed.
> > > > > > 
> > > > > > The following example demonstrates creation of a secret mapping (error
> > > > > > handling is omitted):
> > > > > > 
> > > > > > 	fd = memfd_secret(0);
> > > > > > 	ftruncate(fd, MAP_SIZE);
> > > > > > 	ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> > > > > 
> > > > > I do not see any access control or permission model for this feature.
> > > > > Is this feature generally safe to anybody?
> > > > 
> > > > The mappings obey memlock limit. Besides, this feature should be enabled
> > > > explicitly at boot with the kernel parameter that says what is the maximal
> > > > memory size secretmem can consume.
> > > 
> > > Why is such a model sufficient and future proof? I mean even when it has
> > > to be enabled by an admin it is still all or nothing approach. Mlock
> > > limit is not really useful because it is per mm rather than per user.
> > > 
> > > Is there any reason why this is allowed for non-privileged processes?
> > > Maybe this has been discussed in the past but is there any reason why
> > > this cannot be done by a special device which will allow to provide at
> > > least some permission policy?
> >  
> > Why this should not be allowed for non-privileged processes? This behaves
> > similarly to mlocked memory, so I don't see a reason why secretmem should
> > have different permissions model.
> 
> Because appart from the reclaim aspect it fragments the direct mapping
> IIUC. That might have an impact on all others, right?

Also forgot to mention that you rely on a contiguous allocations and
that can become a very scarce resource so what does prevent one abuser
from using it all and deny the access to others. And unless I am missing
something allocation failure would lead to OOM which cannot really help
because the oom killer cannot compensate for the CMA reservation.
-- 
Michal Hocko
SUSE Labs


  parent reply	other threads:[~2021-01-26  9:20 UTC|newest]

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-21 12:27 [PATCH v16 00/11] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 01/11] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 02/11] mmap: make mlock_future_check() global Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 03/11] riscv/Kconfig: make direct map manipulation options depend on MMU Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 04/11] set_memory: allow set_direct_map_*_noflush() for multiple pages Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 05/11] set_memory: allow querying whether set_direct_map_*() is actually enabled Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 06/11] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-01-25 17:01   ` Michal Hocko
2021-01-25 21:36     ` Mike Rapoport
2021-01-26  7:16       ` Michal Hocko
2021-01-26  8:33         ` Mike Rapoport
2021-01-26  9:00           ` Michal Hocko
2021-01-26  9:20             ` Mike Rapoport
2021-01-26  9:49               ` Michal Hocko
2021-01-26  9:53                 ` David Hildenbrand
2021-01-26 10:19                   ` Michal Hocko
2021-01-26  9:20             ` Michal Hocko [this message]
2021-02-03 12:15   ` Michal Hocko
2021-02-04 11:34     ` Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2021-01-26 11:46   ` Michal Hocko
2021-01-26 11:56     ` David Hildenbrand
2021-01-26 12:08       ` Michal Hocko
2021-01-28  9:22         ` Mike Rapoport
2021-01-28 13:01           ` Michal Hocko
2021-01-28 13:28             ` Christoph Lameter
2021-01-28 13:49               ` Michal Hocko
2021-01-28 15:56                 ` Christoph Lameter
2021-01-28 16:23                   ` Michal Hocko
2021-01-28 15:28             ` James Bottomley
2021-01-29  7:03               ` Mike Rapoport
2021-01-28 21:05             ` James Bottomley
2021-01-29  7:53               ` Michal Hocko
2021-01-29  8:23               ` Michal Hocko
2021-02-01 16:56                 ` James Bottomley
2021-02-02  9:35                   ` Michal Hocko
2021-02-02 12:48                     ` Mike Rapoport
2021-02-02 13:14                       ` David Hildenbrand
2021-02-02 13:32                         ` Michal Hocko
2021-02-02 14:12                           ` David Hildenbrand
2021-02-02 14:22                             ` Michal Hocko
2021-02-02 14:26                               ` David Hildenbrand
2021-02-02 14:32                                 ` Michal Hocko
2021-02-02 14:34                                   ` David Hildenbrand
2021-02-02 18:15                                     ` Mike Rapoport
2021-02-02 18:55                                       ` James Bottomley
2021-02-03 12:09                                         ` Michal Hocko
2021-02-04 11:31                                           ` Mike Rapoport
2021-02-02 13:27                       ` Michal Hocko
2021-02-02 19:10                         ` Mike Rapoport
2021-02-03  9:12                           ` Michal Hocko
2021-02-04  9:58                             ` Mike Rapoport
2021-02-04 13:02                               ` Michal Hocko
2021-01-29  7:21             ` Mike Rapoport
2021-01-29  8:51               ` Michal Hocko
2021-02-02 14:42                 ` David Hildenbrand
2021-01-21 12:27 ` [PATCH v16 08/11] secretmem: add memcg accounting Mike Rapoport
2021-01-25 16:17   ` Matthew Wilcox
2021-01-25 17:18     ` Shakeel Butt
2021-01-25 21:35       ` Mike Rapoport
2021-01-28 15:07         ` Shakeel Butt
2021-01-25 16:54   ` Michal Hocko
2021-01-25 21:38     ` Mike Rapoport
2021-01-26  7:31       ` Michal Hocko
2021-01-26  8:56         ` Mike Rapoport
2021-01-26  9:15           ` Michal Hocko
2021-01-26 14:48       ` Matthew Wilcox
2021-01-26 15:05         ` Michal Hocko
2021-01-27 18:42           ` Roman Gushchin
2021-01-28  7:58             ` Michal Hocko
2021-01-28 14:05               ` Shakeel Butt
2021-01-28 14:22                 ` Michal Hocko
2021-01-28 14:57                   ` Shakeel Butt
2021-01-21 12:27 ` [PATCH v16 09/11] PM: hibernate: disable when there are active secretmem users Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 10/11] arch, mm: wire up memfd_secret system call where relevant Mike Rapoport
2021-01-25 18:18   ` Catalin Marinas
2021-01-21 12:27 ` [PATCH v16 11/11] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2021-01-21 22:18 ` [PATCH v16 00/11] mm: introduce memfd_secret system call to create "secret" memory areas Andrew Morton

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210126092023.GH827@dhcp22.suse.cz \
    --to=mhocko@suse.com \
    --cc=akpm@linux-foundation.org \
    --cc=arnd@arndb.de \
    --cc=bp@alien8.de \
    --cc=catalin.marinas@arm.com \
    --cc=cl@linux.com \
    --cc=dan.j.williams@intel.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=david@redhat.com \
    --cc=elena.reshetova@intel.com \
    --cc=guro@fb.com \
    --cc=hagen@jauu.net \
    --cc=hpa@zytor.com \
    --cc=jejb@linux.ibm.com \
    --cc=kirill@shutemov.name \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-nvdimm@lists.01.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=luto@kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=mingo@redhat.com \
    --cc=mtk.manpages@gmail.com \
    --cc=palmer@dabbelt.com \
    --cc=palmerdabbelt@google.com \
    --cc=paul.walmsley@sifive.com \
    --cc=peterz@infradead.org \
    --cc=rick.p.edgecombe@intel.com \
    --cc=rppt@kernel.org \
    --cc=rppt@linux.ibm.com \
    --cc=shakeelb@google.com \
    --cc=shuah@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=tycho@tycho.ws \
    --cc=viro@zeniv.linux.org.uk \
    --cc=will@kernel.org \
    --cc=willy@infradead.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).