From: Kees Cook <keescook@chromium.org>
To: ira.weiny@intel.com
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, Dave Hansen <dave.hansen@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Vishal Verma <vishal.l.verma@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Fenghua Yu <fenghua.yu@intel.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
Igor Stoppa <igor.stoppa@gmail.com>,
Nadav Amit <nadav.amit@gmail.com>
Subject: Re: [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support
Date: Fri, 24 Jul 2020 15:19:35 -0700 [thread overview]
Message-ID: <202007241455.010B049A@keescook> (raw)
In-Reply-To: <20200717072056.73134-1-ira.weiny@intel.com>
On Fri, Jul 17, 2020 at 12:20:39AM -0700, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> This RFC series has been reviewed by Dave Hansen.
>
> Changes from RFC:
> Clean up commit messages based on Peter Zijlstra's and Dave Hansen's
> feedback
> Fix static branch anti-pattern
> New patch:
> (memremap: Convert devmap static branch to {inc,dec})
> This was the code I used as a model for my static branch which
> I believe is wrong now.
> New Patch:
> (x86/entry: Preserve PKRS MSR through exceptions)
> This attempts to preserve the per-logical-processor MSR, and
> reference counting during exceptions. I'd really like feed
> back on this because I _think_ it should work but I'm afraid
> I'm missing something as my testing has shown a lot of spotty
> crashes which don't make sense to me.
>
> This patch set introduces a new page protection mechanism for supervisor pages,
> Protection Key Supervisor (PKS) and an initial user of them, persistent memory,
> PMEM.
>
> PKS enables protections on 'domains' of supervisor pages to limit supervisor
> mode access to those pages beyond the normal paging protections. They work in
> a similar fashion to user space pkeys. Like User page pkeys (PKU), supervisor
> pkeys are checked in addition to normal paging protections and Access or Writes
> can be disabled via a MSR update without TLB flushes when permissions change.
> A page mapping is assigned to a domain by setting a pkey in the page table
> entry.
>
> Unlike User pkeys no new instructions are added; rather WRMSR/RDMSR are used to
> update the PKRS register.
>
> XSAVE is not supported for the PKRS MSR. To reduce software complexity the
> implementation saves/restores the MSR across context switches but not during
> irqs. This is a compromise which results is a hardening of unwanted access
> without absolute restriction.
>
> For consistent behavior with current paging protections, pkey 0 is reserved and
> configured to allow full access via the pkey mechanism, thus preserving the
> default paging protections on mappings with the default pkey value of 0.
>
> Other keys, (1-15) are allocated by an allocator which prepares us for key
> contention from day one. Kernel users should be prepared for the allocator to
> fail either because of key exhaustion or due to PKS not being supported on the
> arch and/or CPU instance.
>
> Protecting against stray writes is particularly important for PMEM because,
> unlike writes to anonymous memory, writes to PMEM persists across a reboot.
> Thus data corruption could result in permanent loss of data.
>
> The following attributes of PKS makes it perfect as a mechanism to protect PMEM
> from stray access within the kernel:
>
> 1) Fast switching of permissions
> 2) Prevents access without page table manipulations
> 3) Works on a per thread basis
> 4) No TLB flushes required
Cool! This seems like it'd be very handy to make other types of kernel
data "read-only at rest" (as was long ago proposed via X86_CR0_WP[1],
which only provided to protection levels, not 15). For example, I think
at least a few other kinds of areas stand out to me that are in need
of PKS markings (i.e. only things that actually manipulate these areas
should gain temporary PK access):
- Page Tables themselves
- Identity mapping
- The "read-only at rest" stuff, though it'll need special plumbing to
make it work with the slab allocator, etc (more like the later "static
allocation" work[2]).
[1] https://lore.kernel.org/lkml/1490811363-93944-1-git-send-email-keescook@chromium.org/
[2] https://lore.kernel.org/lkml/cover.1550097697.git.igor.stoppa@huawei.com/
--
Kees Cook
prev parent reply other threads:[~2020-07-24 22:19 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 7:20 [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 01/17] x86/pkeys: Create pkeys_internal.h ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 02/17] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support ira.weiny
2020-07-17 8:54 ` Peter Zijlstra
2020-07-17 20:52 ` Ira Weiny
2020-07-20 9:14 ` Peter Zijlstra
2020-07-17 22:36 ` Dave Hansen
2020-07-20 9:13 ` Peter Zijlstra
2020-07-17 7:20 ` [PATCH RFC V2 03/17] x86/pks: Enable Protection Keys Supervisor (PKS) ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch ira.weiny
2020-07-17 8:31 ` Peter Zijlstra
2020-07-17 21:39 ` Ira Weiny
2020-07-17 8:59 ` Peter Zijlstra
2020-07-17 22:34 ` Ira Weiny
2020-07-20 9:15 ` Peter Zijlstra
2020-07-20 18:35 ` Ira Weiny
2020-07-17 7:20 ` [PATCH RFC V2 05/17] x86/pks: Add PKS kernel API ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 06/17] x86/pks: Add a debugfs file for allocated PKS keys ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 07/17] Documentation/pkeys: Update documentation for kernel pkeys ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 08/17] x86/pks: Add PKS Test code ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 09/17] memremap: Convert devmap static branch to {inc,dec} ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 10/17] fs/dax: Remove unused size parameter ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 11/17] drivers/dax: Expand lock scope to cover the use of addresses ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 12/17] memremap: Add zone device access protection ira.weiny
2020-07-17 9:10 ` Peter Zijlstra
2020-07-18 5:06 ` Ira Weiny
2020-07-20 9:16 ` Peter Zijlstra
2020-07-17 9:17 ` Peter Zijlstra
2020-07-18 5:51 ` Ira Weiny
2020-07-17 9:20 ` Peter Zijlstra
2020-07-17 7:20 ` [PATCH RFC V2 13/17] kmap: Add stray write protection for device pages ira.weiny
2020-07-17 9:21 ` Peter Zijlstra
2020-07-19 4:13 ` Ira Weiny
2020-07-20 9:17 ` Peter Zijlstra
2020-07-21 16:31 ` Ira Weiny
2020-07-17 7:20 ` [PATCH RFC V2 14/17] dax: Stray write protection for dax_direct_access() ira.weiny
2020-07-17 9:22 ` Peter Zijlstra
2020-07-19 4:41 ` Ira Weiny
2020-07-17 7:20 ` [PATCH RFC V2 15/17] nvdimm/pmem: Stray write protection for pmem->virt_addr ira.weiny
2020-07-17 7:20 ` [PATCH RFC V2 16/17] [dax|pmem]: Enable stray write protection ira.weiny
2020-07-17 9:25 ` Peter Zijlstra
2020-07-17 7:20 ` [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions ira.weiny
2020-07-17 9:30 ` Peter Zijlstra
2020-07-21 18:01 ` Ira Weiny
2020-07-21 19:11 ` Peter Zijlstra
2020-07-17 9:34 ` Peter Zijlstra
2020-07-17 10:06 ` Peter Zijlstra
2020-07-22 5:27 ` Ira Weiny
2020-07-22 9:48 ` Peter Zijlstra
2020-07-22 21:24 ` Ira Weiny
2020-07-23 20:08 ` Thomas Gleixner
2020-07-23 20:15 ` Thomas Gleixner
2020-07-24 17:23 ` Ira Weiny
2020-07-24 17:29 ` Andy Lutomirski
2020-07-24 19:43 ` Ira Weiny
2020-07-22 16:21 ` Andy Lutomirski
2020-07-23 16:18 ` Fenghua Yu
2020-07-23 16:23 ` Dave Hansen
2020-07-23 16:52 ` Fenghua Yu
2020-07-23 17:08 ` Andy Lutomirski
2020-07-23 17:30 ` Dave Hansen
2020-07-23 20:23 ` Thomas Gleixner
2020-07-23 20:22 ` Thomas Gleixner
2020-07-23 21:30 ` Andy Lutomirski
2020-07-23 22:14 ` Thomas Gleixner
2020-07-23 19:53 ` Thomas Gleixner
2020-07-23 22:04 ` Ira Weiny
2020-07-23 23:41 ` Thomas Gleixner
2020-07-24 21:24 ` Thomas Gleixner
2020-07-24 21:31 ` Thomas Gleixner
2020-07-25 0:09 ` Andy Lutomirski
2020-07-27 20:59 ` Ira Weiny
2020-07-24 22:19 ` Kees Cook [this message]
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