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* [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
@ 2020-09-16  7:28 Mike Rapoport
  2020-09-16 18:49 ` Andy Lutomirski
  0 siblings, 1 reply; 10+ messages in thread
From: Mike Rapoport @ 2020-09-16  7:28 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Alexander Viro, Andy Lutomirski, Arnd Bergmann, Borislav Petkov,
	Catalin Marinas, Christopher Lameter, Dan Williams, Dave Hansen,
	David Hildenbrand, Elena Reshetova, H. Peter Anvin, Idan Yaniv,
	Ingo Molnar, James Bottomley, Kirill A. Shutemov, Matthew Wilcox,
	Mark Rutland, Mike Rapoport, Mike Rapoport, Michael Kerrisk,
	Palmer Dabbelt, Paul Walmsley, Peter Zijlstra, Thomas Gleixner,
	Tycho Andersen, Will Deacon, linux-api, linux-arch,
	linux-arm-kernel, linux-fsdevel, linux-mm, linux-kernel,
	linux-nvdimm, linux-riscv, x86

From: Mike Rapoport <rppt@linux.ibm.com>

Hi,

This is an implementation of "secret" mappings backed by a file descriptor. 
I've dropped the boot time reservation patch for now as it is not strictly
required for the basic usage and can be easily added later either with or
without CMA.

v5 changes:
* rebase on v5.9-rc5
* drop boot time memory reservation patch

v4 changes:
* rebase on v5.9-rc1
* Do not redefine PMD_PAGE_ORDER in fs/dax.c, thanks Kirill
* Make secret mappings exclusive by default and only require flags to
  memfd_secret() system call for uncached mappings, thanks again Kirill :)

v3 changes:
* Squash kernel-parameters.txt update into the commit that added the
  command line option.
* Make uncached mode explicitly selectable by architectures. For now enable
  it only on x86.

v2 changes:
* Follow Michael's suggestion and name the new system call 'memfd_secret'
* Add kernel-parameters documentation about the boot option
* Fix i386-tinyconfig regression reported by the kbuild bot.
  CONFIG_SECRETMEM now depends on !EMBEDDED to disable it on small systems
  from one side and still make it available unconditionally on
  architectures that support SET_DIRECT_MAP.

The file descriptor backing secret memory mappings is created using a
dedicated memfd_secret system call The desired protection mode for the
memory is configured using flags parameter of the system call. The mmap()
of the file descriptor created with memfd_secret() will create a "secret"
memory mapping. The pages in that mapping will be marked as not present in
the direct map and will have desired protection bits set in the user page
table. For instance, current implementation allows uncached mappings.

Although normally Linux userspace mappings are protected from other users, 
such secret mappings are useful for environments where a hostile tenant is
trying to trick the kernel into giving them access to other tenants
mappings.

Additionally, the secret mappings may be used as a mean to protect guest
memory in a virtual machine host.

For demonstration of secret memory usage we've created a userspace library
[1] that does two things: the first is act as a preloader for openssl to
redirect all the OPENSSL_malloc calls to secret memory meaning any secret
keys get automatically protected this way and the other thing it does is
expose the API to the user who needs it. We anticipate that a lot of the
use cases would be like the openssl one: many toolkits that deal with
secret keys already have special handling for the memory to try to give
them greater protection, so this would simply be pluggable into the
toolkits without any need for user application modification.

I've hesitated whether to continue to use new flags to memfd_create() or to
add a new system call and I've decided to use a new system call after I've
started to look into man pages update. There would have been two completely
independent descriptions and I think it would have been very confusing.

Hiding secret memory mappings behind an anonymous file allows (ab)use of
the page cache for tracking pages allocated for the "secret" mappings as
well as using address_space_operations for e.g. page migration callbacks.

The anonymous file may be also used implicitly, like hugetlb files, to
implement mmap(MAP_SECRET) and use the secret memory areas with "native" mm
ABIs in the future.

As the fragmentation of the direct map was one of the major concerns raised
during the previous postings, I've added an amortizing cache of PMD-size
pages to each file descriptor that is used as an allocation pool for the
secret memory areas.

v4: https://lore.kernel.org/lkml/20200818141554.13945-1-rppt@kernel.org
v3: https://lore.kernel.org/lkml/20200804095035.18778-1-rppt@kernel.org
v2: https://lore.kernel.org/lkml/20200727162935.31714-1-rppt@kernel.org
v1: https://lore.kernel.org/lkml/20200720092435.17469-1-rppt@kernel.org/
rfc-v2: https://lore.kernel.org/lkml/20200706172051.19465-1-rppt@kernel.org/
rfc-v1: https://lore.kernel.org/lkml/20200130162340.GA14232@rapoport-lnx/


Mike Rapoport (5):
  mm: add definition of PMD_PAGE_ORDER
  mmap: make mlock_future_check() global
  mm: introduce memfd_secret system call to create "secret" memory areas
  arch, mm: wire up memfd_secret system call were relevant
  mm: secretmem: use PMD-size pages to amortize direct map fragmentation

 arch/Kconfig                           |   7 +
 arch/arm64/include/asm/unistd.h        |   2 +-
 arch/arm64/include/asm/unistd32.h      |   2 +
 arch/arm64/include/uapi/asm/unistd.h   |   1 +
 arch/riscv/include/asm/unistd.h        |   1 +
 arch/x86/Kconfig                       |   1 +
 arch/x86/entry/syscalls/syscall_32.tbl |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl |   1 +
 fs/dax.c                               |  11 +-
 include/linux/pgtable.h                |   3 +
 include/linux/syscalls.h               |   1 +
 include/uapi/asm-generic/unistd.h      |   7 +-
 include/uapi/linux/magic.h             |   1 +
 include/uapi/linux/secretmem.h         |   8 +
 kernel/sys_ni.c                        |   2 +
 mm/Kconfig                             |   4 +
 mm/Makefile                            |   1 +
 mm/internal.h                          |   3 +
 mm/mmap.c                              |   5 +-
 mm/secretmem.c                         | 333 +++++++++++++++++++++++++
 20 files changed, 383 insertions(+), 12 deletions(-)
 create mode 100644 include/uapi/linux/secretmem.h
 create mode 100644 mm/secretmem.c

-- 
2.28.0


^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
  2020-09-16  7:28 [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
@ 2020-09-16 18:49 ` Andy Lutomirski
  0 siblings, 0 replies; 10+ messages in thread
From: Andy Lutomirski @ 2020-09-16 18:49 UTC (permalink / raw)
  To: Mike Rapoport
  Cc: Andrew Morton, Alexander Viro, Andy Lutomirski, Arnd Bergmann,
	Borislav Petkov, Catalin Marinas, Christopher Lameter,
	Dan Williams, Dave Hansen, David Hildenbrand, Elena Reshetova,
	H. Peter Anvin, Idan Yaniv, Ingo Molnar, James Bottomley,
	Kirill A. Shutemov, Matthew Wilcox, Mark Rutland, Mike Rapoport,
	Michael Kerrisk, Palmer Dabbelt, Paul Walmsley, Peter Zijlstra,
	Thomas Gleixner, Tycho Andersen, Will Deacon, Linux API,
	linux-arch, linux-arm-kernel, Linux FS Devel, Linux-MM, LKML,
	linux-nvdimm, linux-riscv, X86 ML

On Wed, Sep 16, 2020 at 12:28 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> Hi,
>
> This is an implementation of "secret" mappings backed by a file descriptor.
> I've dropped the boot time reservation patch for now as it is not strictly
> required for the basic usage and can be easily added later either with or
> without CMA.
>
> v5 changes:
> * rebase on v5.9-rc5
> * drop boot time memory reservation patch
>
> v4 changes:
> * rebase on v5.9-rc1
> * Do not redefine PMD_PAGE_ORDER in fs/dax.c, thanks Kirill
> * Make secret mappings exclusive by default and only require flags to
>   memfd_secret() system call for uncached mappings, thanks again Kirill :)
>
> v3 changes:
> * Squash kernel-parameters.txt update into the commit that added the
>   command line option.
> * Make uncached mode explicitly selectable by architectures. For now enable
>   it only on x86.
>
> v2 changes:
> * Follow Michael's suggestion and name the new system call 'memfd_secret'
> * Add kernel-parameters documentation about the boot option
> * Fix i386-tinyconfig regression reported by the kbuild bot.
>   CONFIG_SECRETMEM now depends on !EMBEDDED to disable it on small systems
>   from one side and still make it available unconditionally on
>   architectures that support SET_DIRECT_MAP.
>
> The file descriptor backing secret memory mappings is created using a
> dedicated memfd_secret system call The desired protection mode for the
> memory is configured using flags parameter of the system call. The mmap()
> of the file descriptor created with memfd_secret() will create a "secret"
> memory mapping. The pages in that mapping will be marked as not present in
> the direct map and will have desired protection bits set in the user page
> table. For instance, current implementation allows uncached mappings.

I still have serious concerns with uncached mappings.  I'm not saying
I can't be convinced, but I'm not currently convinced that we should
allow user code to create UC mappings on x86.

--Andy

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
  2020-09-18 18:25   ` Qian Cai
@ 2020-09-21  8:07     ` Stephen Rothwell
  0 siblings, 0 replies; 10+ messages in thread
From: Stephen Rothwell @ 2020-09-21  8:07 UTC (permalink / raw)
  To: Qian Cai
  Cc: Mike Rapoport, Andrew Morton, Alexander Viro, Andy Lutomirski,
	Arnd Bergmann, Borislav Petkov, Catalin Marinas,
	Christopher Lameter, Dan Williams, Dave Hansen,
	David Hildenbrand, Elena Reshetova, H. Peter Anvin, Idan Yaniv,
	Ingo Molnar, James Bottomley, Kirill A. Shutemov, Matthew Wilcox,
	Mark Rutland, Mike Rapoport, Michael Kerrisk, Palmer Dabbelt,
	Paul Walmsley, Peter Zijlstra, Thomas Gleixner, Tycho Andersen,
	Will Deacon, linux-api, linux-arch, linux-arm-kernel,
	linux-fsdevel, linux-mm, linux-kernel, linux-nvdimm, linux-riscv,
	x86, linux-next

[-- Attachment #1: Type: text/plain, Size: 1326 bytes --]

Hi all,

On Fri, 18 Sep 2020 14:25:15 -0400 Qian Cai <cai@redhat.com> wrote:
>
> On Thu, 2020-09-17 at 09:27 -0400, Qian Cai wrote:
> > On Wed, 2020-09-16 at 10:35 +0300, Mike Rapoport wrote:  
> > > From: Mike Rapoport <rppt@linux.ibm.com>
> > > 
> > > This is an implementation of "secret" mappings backed by a file descriptor. 
> > > I've dropped the boot time reservation patch for now as it is not strictly
> > > required for the basic usage and can be easily added later either with or
> > > without CMA.  
> > 
> > On powerpc: https://gitlab.com/cailca/linux-mm/-/blob/master/powerpc.config
> > 
> > There is a compiling warning from the today's linux-next:
> > 
> > <stdin>:1532:2: warning: #warning syscall memfd_secret not implemented [-Wcpp]  
> 
> This should silence the warning:
> 
> diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
> index a18b47695f55..b7609958ee36 100755
> --- a/scripts/checksyscalls.sh
> +++ b/scripts/checksyscalls.sh
> @@ -40,6 +40,10 @@ cat << EOF
>  #define __IGNORE_setrlimit	/* setrlimit */
>  #endif
>  
> +#ifndef __ARCH_WANT_MEMFD_SECRET
> +#define __IGNORE_memfd_secret
> +#endif
> +
>  /* Missing flags argument */
>  #define __IGNORE_renameat	/* renameat2 */
> 

Added to linux-next today.

-- 
Cheers,
Stephen Rothwell

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
  2020-09-17 13:27 ` Qian Cai
@ 2020-09-18 18:25   ` Qian Cai
  2020-09-21  8:07     ` Stephen Rothwell
  0 siblings, 1 reply; 10+ messages in thread
From: Qian Cai @ 2020-09-18 18:25 UTC (permalink / raw)
  To: Mike Rapoport, Andrew Morton
  Cc: Alexander Viro, Andy Lutomirski, Arnd Bergmann, Borislav Petkov,
	Catalin Marinas, Christopher Lameter, Dan Williams, Dave Hansen,
	David Hildenbrand, Elena Reshetova, H. Peter Anvin, Idan Yaniv,
	Ingo Molnar, James Bottomley, Kirill A. Shutemov, Matthew Wilcox,
	Mark Rutland, Mike Rapoport, Michael Kerrisk, Palmer Dabbelt,
	Paul Walmsley, Peter Zijlstra, Thomas Gleixner, Tycho Andersen,
	Will Deacon, linux-api, linux-arch, linux-arm-kernel,
	linux-fsdevel, linux-mm, linux-kernel, linux-nvdimm, linux-riscv,
	x86, Stephen Rothwell, linux-next

On Thu, 2020-09-17 at 09:27 -0400, Qian Cai wrote:
> On Wed, 2020-09-16 at 10:35 +0300, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > 
> > Hi,
> > 
> > This is an implementation of "secret" mappings backed by a file descriptor. 
> > I've dropped the boot time reservation patch for now as it is not strictly
> > required for the basic usage and can be easily added later either with or
> > without CMA.
> 
> On powerpc: https://gitlab.com/cailca/linux-mm/-/blob/master/powerpc.config
> 
> There is a compiling warning from the today's linux-next:
> 
> <stdin>:1532:2: warning: #warning syscall memfd_secret not implemented [-Wcpp]

This should silence the warning:

diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
index a18b47695f55..b7609958ee36 100755
--- a/scripts/checksyscalls.sh
+++ b/scripts/checksyscalls.sh
@@ -40,6 +40,10 @@ cat << EOF
 #define __IGNORE_setrlimit	/* setrlimit */
 #endif
 
+#ifndef __ARCH_WANT_MEMFD_SECRET
+#define __IGNORE_memfd_secret
+#endif
+
 /* Missing flags argument */
 #define __IGNORE_renameat	/* renameat2 */


^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
  2020-09-16  7:35 Mike Rapoport
  2020-09-16 23:20 ` Andrew Morton
@ 2020-09-17 13:27 ` Qian Cai
  2020-09-18 18:25   ` Qian Cai
  1 sibling, 1 reply; 10+ messages in thread
From: Qian Cai @ 2020-09-17 13:27 UTC (permalink / raw)
  To: Mike Rapoport, Andrew Morton
  Cc: Alexander Viro, Andy Lutomirski, Arnd Bergmann, Borislav Petkov,
	Catalin Marinas, Christopher Lameter, Dan Williams, Dave Hansen,
	David Hildenbrand, Elena Reshetova, H. Peter Anvin, Idan Yaniv,
	Ingo Molnar, James Bottomley, Kirill A. Shutemov, Matthew Wilcox,
	Mark Rutland, Mike Rapoport, Michael Kerrisk, Palmer Dabbelt,
	Paul Walmsley, Peter Zijlstra, Thomas Gleixner, Tycho Andersen,
	Will Deacon, linux-api, linux-arch, linux-arm-kernel,
	linux-fsdevel, linux-mm, linux-kernel, linux-nvdimm, linux-riscv,
	x86, Stephen Rothwell, linux-next

On Wed, 2020-09-16 at 10:35 +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> Hi,
> 
> This is an implementation of "secret" mappings backed by a file descriptor. 
> I've dropped the boot time reservation patch for now as it is not strictly
> required for the basic usage and can be easily added later either with or
> without CMA.

On powerpc: https://gitlab.com/cailca/linux-mm/-/blob/master/powerpc.config

There is a compiling warning from the today's linux-next:

<stdin>:1532:2: warning: #warning syscall memfd_secret not implemented [-Wcpp]


^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
  2020-09-17  5:46   ` Michael Kerrisk (man-pages)
@ 2020-09-17  6:02     ` Mike Rapoport
  0 siblings, 0 replies; 10+ messages in thread
From: Mike Rapoport @ 2020-09-17  6:02 UTC (permalink / raw)
  To: Michael Kerrisk (man-pages)
  Cc: Andrew Morton, Alexander Viro, Andy Lutomirski, Arnd Bergmann,
	Borislav Petkov, Catalin Marinas, Christopher Lameter,
	Dan Williams, Dave Hansen, David Hildenbrand, Elena Reshetova,
	H. Peter Anvin, Idan Yaniv, Ingo Molnar, James Bottomley,
	Kirill A. Shutemov, Matthew Wilcox, Mark Rutland, Mike Rapoport,
	Palmer Dabbelt, Paul Walmsley, Peter Zijlstra, Thomas Gleixner,
	Tycho Andersen, Will Deacon, Linux API, linux-arch,
	linux-arm-kernel, linux-fsdevel, Linux-MM, lkml, linux-nvdimm,
	linux-riscv, maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)

On Thu, Sep 17, 2020 at 07:46:12AM +0200, Michael Kerrisk (man-pages) wrote:
> On Thu, 17 Sep 2020 at 01:20, Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Wed, 16 Sep 2020 10:35:34 +0300 Mike Rapoport <rppt@kernel.org> wrote:
> >
> > > This is an implementation of "secret" mappings backed by a file descriptor.
> > > I've dropped the boot time reservation patch for now as it is not strictly
> > > required for the basic usage and can be easily added later either with or
> > > without CMA.
> >
> > It seems early days for this, especially as regards reviewer buyin.
> > But I'll toss it in there to get it some additional testing.
> >
> > A test suite in tools/testging/selftests/ would be helpful, especially
> > for arch maintainers.
> >
> > I assume that user-facing manpage alterations are planned?

> I was just about to write a mail into this thread when I saw this :-).
> 
> So far, I don't think I saw a manual page patch. Mike, how about it?

It is planned :)

I have a draft, but I'm waiting for consensus about the uncached
mappings before sending it out.

-- 
Sincerely yours,
Mike.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
  2020-09-16 23:20 ` Andrew Morton
  2020-09-17  5:46   ` Michael Kerrisk (man-pages)
@ 2020-09-17  6:00   ` Mike Rapoport
  1 sibling, 0 replies; 10+ messages in thread
From: Mike Rapoport @ 2020-09-17  6:00 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Alexander Viro, Andy Lutomirski, Arnd Bergmann, Borislav Petkov,
	Catalin Marinas, Christopher Lameter, Dan Williams, Dave Hansen,
	David Hildenbrand, Elena Reshetova, H. Peter Anvin, Idan Yaniv,
	Ingo Molnar, James Bottomley, Kirill A. Shutemov, Matthew Wilcox,
	Mark Rutland, Mike Rapoport, Michael Kerrisk, Palmer Dabbelt,
	Paul Walmsley, Peter Zijlstra, Thomas Gleixner, Tycho Andersen,
	Will Deacon, linux-api, linux-arch, linux-arm-kernel,
	linux-fsdevel, linux-mm, linux-kernel, linux-nvdimm, linux-riscv,
	x86

On Wed, Sep 16, 2020 at 04:20:20PM -0700, Andrew Morton wrote:
> On Wed, 16 Sep 2020 10:35:34 +0300 Mike Rapoport <rppt@kernel.org> wrote:
> 
> > This is an implementation of "secret" mappings backed by a file descriptor. 
> > I've dropped the boot time reservation patch for now as it is not strictly
> > required for the basic usage and can be easily added later either with or
> > without CMA.
> 
> It seems early days for this, especially as regards reviewer buyin. 
> But I'll toss it in there to get it some additional testing.

Thanks!

> A test suite in tools/testging/selftests/ would be helpful, especially
> for arch maintainers.

I'll look into it.

> I assume that user-facing manpage alterations are planned?

Of course.

-- 
Sincerely yours,
Mike.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
  2020-09-16 23:20 ` Andrew Morton
@ 2020-09-17  5:46   ` Michael Kerrisk (man-pages)
  2020-09-17  6:02     ` Mike Rapoport
  2020-09-17  6:00   ` Mike Rapoport
  1 sibling, 1 reply; 10+ messages in thread
From: Michael Kerrisk (man-pages) @ 2020-09-17  5:46 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Mike Rapoport, Alexander Viro, Andy Lutomirski, Arnd Bergmann,
	Borislav Petkov, Catalin Marinas, Christopher Lameter,
	Dan Williams, Dave Hansen, David Hildenbrand, Elena Reshetova,
	H. Peter Anvin, Idan Yaniv, Ingo Molnar, James Bottomley,
	Kirill A. Shutemov, Matthew Wilcox, Mark Rutland, Mike Rapoport,
	Palmer Dabbelt, Paul Walmsley, Peter Zijlstra, Thomas Gleixner,
	Tycho Andersen, Will Deacon, Linux API, linux-arch,
	linux-arm-kernel, linux-fsdevel, Linux-MM, lkml, linux-nvdimm,
	linux-riscv, maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)

On Thu, 17 Sep 2020 at 01:20, Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Wed, 16 Sep 2020 10:35:34 +0300 Mike Rapoport <rppt@kernel.org> wrote:
>
> > This is an implementation of "secret" mappings backed by a file descriptor.
> > I've dropped the boot time reservation patch for now as it is not strictly
> > required for the basic usage and can be easily added later either with or
> > without CMA.
>
> It seems early days for this, especially as regards reviewer buyin.
> But I'll toss it in there to get it some additional testing.
>
> A test suite in tools/testging/selftests/ would be helpful, especially
> for arch maintainers.
>
> I assume that user-facing manpage alterations are planned?

I was just about to write a mail into this thread when I saw this :-).

So far, I don't think I saw a manual page patch. Mike, how about it?

Thanks,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
  2020-09-16  7:35 Mike Rapoport
@ 2020-09-16 23:20 ` Andrew Morton
  2020-09-17  5:46   ` Michael Kerrisk (man-pages)
  2020-09-17  6:00   ` Mike Rapoport
  2020-09-17 13:27 ` Qian Cai
  1 sibling, 2 replies; 10+ messages in thread
From: Andrew Morton @ 2020-09-16 23:20 UTC (permalink / raw)
  To: Mike Rapoport
  Cc: Alexander Viro, Andy Lutomirski, Arnd Bergmann, Borislav Petkov,
	Catalin Marinas, Christopher Lameter, Dan Williams, Dave Hansen,
	David Hildenbrand, Elena Reshetova, H. Peter Anvin, Idan Yaniv,
	Ingo Molnar, James Bottomley, Kirill A. Shutemov, Matthew Wilcox,
	Mark Rutland, Mike Rapoport, Michael Kerrisk, Palmer Dabbelt,
	Paul Walmsley, Peter Zijlstra, Thomas Gleixner, Tycho Andersen,
	Will Deacon, linux-api, linux-arch, linux-arm-kernel,
	linux-fsdevel, linux-mm, linux-kernel, linux-nvdimm, linux-riscv,
	x86

On Wed, 16 Sep 2020 10:35:34 +0300 Mike Rapoport <rppt@kernel.org> wrote:

> This is an implementation of "secret" mappings backed by a file descriptor. 
> I've dropped the boot time reservation patch for now as it is not strictly
> required for the basic usage and can be easily added later either with or
> without CMA.

It seems early days for this, especially as regards reviewer buyin. 
But I'll toss it in there to get it some additional testing.

A test suite in tools/testging/selftests/ would be helpful, especially
for arch maintainers.

I assume that user-facing manpage alterations are planned?

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
@ 2020-09-16  7:35 Mike Rapoport
  2020-09-16 23:20 ` Andrew Morton
  2020-09-17 13:27 ` Qian Cai
  0 siblings, 2 replies; 10+ messages in thread
From: Mike Rapoport @ 2020-09-16  7:35 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Alexander Viro, Andy Lutomirski, Arnd Bergmann, Borislav Petkov,
	Catalin Marinas, Christopher Lameter, Dan Williams, Dave Hansen,
	David Hildenbrand, Elena Reshetova, H. Peter Anvin, Idan Yaniv,
	Ingo Molnar, James Bottomley, Kirill A. Shutemov, Matthew Wilcox,
	Mark Rutland, Mike Rapoport, Mike Rapoport, Michael Kerrisk,
	Palmer Dabbelt, Paul Walmsley, Peter Zijlstra, Thomas Gleixner,
	Tycho Andersen, Will Deacon, linux-api, linux-arch,
	linux-arm-kernel, linux-fsdevel, linux-mm, linux-kernel,
	linux-nvdimm, linux-riscv, x86

From: Mike Rapoport <rppt@linux.ibm.com>

Hi,

This is an implementation of "secret" mappings backed by a file descriptor. 
I've dropped the boot time reservation patch for now as it is not strictly
required for the basic usage and can be easily added later either with or
without CMA.

v5 changes:
* rebase on v5.9-rc5
* drop boot time memory reservation patch

v4 changes:
* rebase on v5.9-rc1
* Do not redefine PMD_PAGE_ORDER in fs/dax.c, thanks Kirill
* Make secret mappings exclusive by default and only require flags to
  memfd_secret() system call for uncached mappings, thanks again Kirill :)

v3 changes:
* Squash kernel-parameters.txt update into the commit that added the
  command line option.
* Make uncached mode explicitly selectable by architectures. For now enable
  it only on x86.

v2 changes:
* Follow Michael's suggestion and name the new system call 'memfd_secret'
* Add kernel-parameters documentation about the boot option
* Fix i386-tinyconfig regression reported by the kbuild bot.
  CONFIG_SECRETMEM now depends on !EMBEDDED to disable it on small systems
  from one side and still make it available unconditionally on
  architectures that support SET_DIRECT_MAP.

The file descriptor backing secret memory mappings is created using a
dedicated memfd_secret system call The desired protection mode for the
memory is configured using flags parameter of the system call. The mmap()
of the file descriptor created with memfd_secret() will create a "secret"
memory mapping. The pages in that mapping will be marked as not present in
the direct map and will have desired protection bits set in the user page
table. For instance, current implementation allows uncached mappings.

Although normally Linux userspace mappings are protected from other users, 
such secret mappings are useful for environments where a hostile tenant is
trying to trick the kernel into giving them access to other tenants
mappings.

Additionally, the secret mappings may be used as a mean to protect guest
memory in a virtual machine host.

For demonstration of secret memory usage we've created a userspace library
[1] that does two things: the first is act as a preloader for openssl to
redirect all the OPENSSL_malloc calls to secret memory meaning any secret
keys get automatically protected this way and the other thing it does is
expose the API to the user who needs it. We anticipate that a lot of the
use cases would be like the openssl one: many toolkits that deal with
secret keys already have special handling for the memory to try to give
them greater protection, so this would simply be pluggable into the
toolkits without any need for user application modification.

I've hesitated whether to continue to use new flags to memfd_create() or to
add a new system call and I've decided to use a new system call after I've
started to look into man pages update. There would have been two completely
independent descriptions and I think it would have been very confusing.

Hiding secret memory mappings behind an anonymous file allows (ab)use of
the page cache for tracking pages allocated for the "secret" mappings as
well as using address_space_operations for e.g. page migration callbacks.

The anonymous file may be also used implicitly, like hugetlb files, to
implement mmap(MAP_SECRET) and use the secret memory areas with "native" mm
ABIs in the future.

As the fragmentation of the direct map was one of the major concerns raised
during the previous postings, I've added an amortizing cache of PMD-size
pages to each file descriptor that is used as an allocation pool for the
secret memory areas.

v4: https://lore.kernel.org/lkml/20200818141554.13945-1-rppt@kernel.org
v3: https://lore.kernel.org/lkml/20200804095035.18778-1-rppt@kernel.org
v2: https://lore.kernel.org/lkml/20200727162935.31714-1-rppt@kernel.org
v1: https://lore.kernel.org/lkml/20200720092435.17469-1-rppt@kernel.org/
rfc-v2: https://lore.kernel.org/lkml/20200706172051.19465-1-rppt@kernel.org/
rfc-v1: https://lore.kernel.org/lkml/20200130162340.GA14232@rapoport-lnx/


Mike Rapoport (5):
  mm: add definition of PMD_PAGE_ORDER
  mmap: make mlock_future_check() global
  mm: introduce memfd_secret system call to create "secret" memory areas
  arch, mm: wire up memfd_secret system call were relevant
  mm: secretmem: use PMD-size pages to amortize direct map fragmentation

 arch/Kconfig                           |   7 +
 arch/arm64/include/asm/unistd.h        |   2 +-
 arch/arm64/include/asm/unistd32.h      |   2 +
 arch/arm64/include/uapi/asm/unistd.h   |   1 +
 arch/riscv/include/asm/unistd.h        |   1 +
 arch/x86/Kconfig                       |   1 +
 arch/x86/entry/syscalls/syscall_32.tbl |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl |   1 +
 fs/dax.c                               |  11 +-
 include/linux/pgtable.h                |   3 +
 include/linux/syscalls.h               |   1 +
 include/uapi/asm-generic/unistd.h      |   7 +-
 include/uapi/linux/magic.h             |   1 +
 include/uapi/linux/secretmem.h         |   8 +
 kernel/sys_ni.c                        |   2 +
 mm/Kconfig                             |   4 +
 mm/Makefile                            |   1 +
 mm/internal.h                          |   3 +
 mm/mmap.c                              |   5 +-
 mm/secretmem.c                         | 333 +++++++++++++++++++++++++
 20 files changed, 383 insertions(+), 12 deletions(-)
 create mode 100644 include/uapi/linux/secretmem.h
 create mode 100644 mm/secretmem.c

-- 
2.28.0


^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2020-09-21  8:08 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-16  7:28 [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-09-16 18:49 ` Andy Lutomirski
2020-09-16  7:35 Mike Rapoport
2020-09-16 23:20 ` Andrew Morton
2020-09-17  5:46   ` Michael Kerrisk (man-pages)
2020-09-17  6:02     ` Mike Rapoport
2020-09-17  6:00   ` Mike Rapoport
2020-09-17 13:27 ` Qian Cai
2020-09-18 18:25   ` Qian Cai
2020-09-21  8:07     ` Stephen Rothwell

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