From: Kees Cook <keescook@chromium.org>
To: Jann Horn <jannh@google.com>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>,
x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H . J . Lu" <hjl.tools@gmail.com>,
Jonathan Corbet <corbet@lwn.net>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V . Shankar" <ravi.v.shankar@intel.com>,
Weijiang Yang <weijiang.yang@intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
joao.moreira@intel.com, John Allen <john.allen@amd.com>,
kcc@google.com, eranian@google.com, rppt@kernel.org,
jamorris@linux.microsoft.com, dethoma@microsoft.com
Subject: Re: [PATCH v2 00/39] Shadowstacks for userspace
Date: Mon, 3 Oct 2022 22:01:07 -0700 [thread overview]
Message-ID: <202210032158.CE0941C4D@keescook> (raw)
In-Reply-To: <CAG48ez2TGdwcr-jUPm1EL1D6X2a-wbx+gXLZUq46qxO-FTctHQ@mail.gmail.com>
On Mon, Oct 03, 2022 at 07:25:03PM +0200, Jann Horn wrote:
> On Mon, Oct 3, 2022 at 7:04 PM Kees Cook <keescook@chromium.org> wrote:
> > On Thu, Sep 29, 2022 at 03:28:57PM -0700, Rick Edgecombe wrote:
> > > This is an overdue followup to the “Shadow stacks for userspace” CET series.
> > > Thanks for all the comments on the first version [0]. They drove a decent
> > > amount of changes for v2. Since it has been awhile, I’ll try to summarize the
> > > areas that got major changes since last time. Smaller changes are listed in
> > > each patch.
> >
> > Thanks for the write-up!
> >
> > > [...]
> > > GUP
> > > ---
> > > Shadow stack memory is generally treated as writable by the kernel, but
> > > it behaves differently then other writable memory with respect to GUP.
> > > FOLL_WRITE will not GUP shadow stack memory unless FOLL_FORCE is also
> > > set. Shadow stack memory is writable from the perspective of being
> > > changeable by userspace, but it is also protected memory from
> > > userspace’s perspective. So preventing it from being writable via
> > > FOLL_WRITE help’s make it harder for userspace to arbitrarily write to
> > > it. However, like read-only memory, FOLL_FORCE can still write through
> > > it. This means shadow stacks can be written to via things like
> > > “/proc/self/mem”. Apps that want extra security will have to prevent
> > > access to kernel features that can write with FOLL_FORCE.
> >
> > This seems like a problem to me -- the point of SS is that there cannot be
> > a way to write to them without specific instruction sequences. The fact
> > that /proc/self/mem bypasses memory protections was an old design mistake
> > that keeps leading to surprising behaviors. It would be much nicer to
> > draw the line somewhere and just say that FOLL_FORCE doesn't work on
> > VM_SHADOW_STACK. Why must FOLL_FORCE be allowed to write to SS?
>
> But once you have FOLL_FORCE, you can also just write over stuff like
> executable code instead of writing over the stack. I don't think
> allowing FOLL_FORCE writes over shadow stacks from /proc/$pid/mem is
> making things worse in any way, and it's probably helpful for stuff
> like debuggers.
>
> If you don't want /proc/$pid/mem to be able to do stuff like that,
> then IMO the way to go is to change when /proc/$pid/mem uses
> FOLL_FORCE, or to limit overall write access to /proc/$pid/mem.
Yeah, all reasonable. I just wish we could ditch FOLL_FORCE; it continues
to weird me out how powerful that fd's side-effects are.
--
Kees Cook
next prev parent reply other threads:[~2022-10-04 5:01 UTC|newest]
Thread overview: 241+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-29 22:28 [PATCH v2 00/39] Shadowstacks for userspace Rick Edgecombe
2022-09-29 22:28 ` [PATCH v2 01/39] Documentation/x86: Add CET description Rick Edgecombe
2022-09-30 3:41 ` Bagas Sanjaya
2022-09-30 13:33 ` Jonathan Corbet
2022-09-30 13:41 ` Bagas Sanjaya
2022-10-03 16:56 ` Edgecombe, Rick P
2022-10-04 2:16 ` Bagas Sanjaya
2022-10-05 9:10 ` Peter Zijlstra
2022-10-05 9:25 ` Bagas Sanjaya
2022-10-05 9:46 ` Peter Zijlstra
2022-10-03 19:35 ` John Hubbard
2022-10-03 19:39 ` Dave Hansen
2022-10-04 2:13 ` Bagas Sanjaya
2022-10-03 17:18 ` Kees Cook
2022-10-03 19:46 ` Edgecombe, Rick P
2022-10-05 0:02 ` Andrew Cooper
2022-10-10 12:19 ` Florian Weimer
2022-10-10 16:44 ` Edgecombe, Rick P
2022-10-10 16:51 ` H.J. Lu
2022-10-12 12:29 ` Florian Weimer
2022-10-12 15:59 ` Dave Hansen
2022-10-12 16:54 ` Florian Weimer
2022-10-13 21:28 ` Edgecombe, Rick P
2022-10-13 22:15 ` H.J. Lu
2022-10-26 21:59 ` Edgecombe, Rick P
2022-09-29 22:28 ` [PATCH v2 02/39] x86/cet/shstk: Add Kconfig option for Shadow Stack Rick Edgecombe
2022-10-03 13:40 ` Kirill A . Shutemov
2022-10-03 19:53 ` Edgecombe, Rick P
2022-10-03 17:25 ` Kees Cook
2022-10-03 19:52 ` Edgecombe, Rick P
2022-10-03 19:42 ` Dave Hansen
2022-10-03 19:50 ` Edgecombe, Rick P
2022-10-12 20:04 ` Borislav Petkov
2022-10-13 0:31 ` Edgecombe, Rick P
2022-10-13 9:21 ` Borislav Petkov
2022-09-29 22:29 ` [PATCH v2 03/39] x86/cpufeatures: Add CPU feature flags for shadow stacks Rick Edgecombe
2022-10-03 17:26 ` Kees Cook
2022-10-14 16:20 ` Borislav Petkov
2022-10-14 19:35 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 04/39] x86/cpufeatures: Enable CET CR4 bit for shadow stack Rick Edgecombe
2022-10-03 17:31 ` Kees Cook
2022-10-05 0:55 ` Andrew Cooper
2022-10-14 17:12 ` Borislav Petkov
2022-10-14 18:15 ` Edgecombe, Rick P
2022-10-14 19:44 ` Borislav Petkov
2022-09-29 22:29 ` [PATCH v2 05/39] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Rick Edgecombe
2022-10-03 17:40 ` Kees Cook
2022-10-15 9:46 ` Borislav Petkov
2022-10-17 18:57 ` Edgecombe, Rick P
2022-10-17 19:33 ` Borislav Petkov
2022-09-29 22:29 ` [PATCH v2 06/39] x86/fpu: Add helper for modifying xstate Rick Edgecombe
2022-10-03 17:48 ` Kees Cook
2022-10-03 20:05 ` Edgecombe, Rick P
2022-10-04 4:05 ` Kees Cook
2022-10-04 14:18 ` Dave Hansen
2022-10-04 16:13 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 07/39] x86/cet: Add user control-protection fault handler Rick Edgecombe
2022-10-03 14:01 ` Kirill A . Shutemov
2022-10-03 18:12 ` Edgecombe, Rick P
2022-10-03 18:04 ` Kees Cook
2022-10-03 20:33 ` Edgecombe, Rick P
2022-10-03 22:51 ` Andy Lutomirski
2022-10-03 23:09 ` H. Peter Anvin
2022-10-03 23:11 ` Edgecombe, Rick P
2022-10-05 1:20 ` Andrew Cooper
2022-10-05 22:44 ` Edgecombe, Rick P
2022-10-05 9:39 ` Peter Zijlstra
2022-10-05 22:45 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 08/39] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Rick Edgecombe
2022-10-03 14:17 ` Kirill A . Shutemov
2022-10-05 1:31 ` Andrew Cooper
2022-10-05 11:16 ` Peter Zijlstra
2022-10-05 12:34 ` Andrew Cooper
2022-09-29 22:29 ` [PATCH v2 09/39] x86/mm: Move pmd_write(), pud_write() up in the file Rick Edgecombe
2022-10-03 18:06 ` Kees Cook
2022-09-29 22:29 ` [PATCH v2 10/39] x86/mm: Introduce _PAGE_COW Rick Edgecombe
2022-09-30 15:16 ` Jann Horn
2022-10-06 16:10 ` Edgecombe, Rick P
2022-10-03 16:26 ` Kirill A . Shutemov
2022-10-03 21:36 ` Edgecombe, Rick P
2022-10-03 21:54 ` Jann Horn
2022-10-03 22:20 ` Edgecombe, Rick P
2022-10-03 22:14 ` Dave Hansen
2022-10-05 2:17 ` Andrew Cooper
2022-10-05 14:08 ` Dave Hansen
2022-10-05 23:06 ` Edgecombe, Rick P
2022-10-05 23:01 ` Edgecombe, Rick P
2022-10-05 11:33 ` Peter Zijlstra
2022-10-14 9:41 ` Peter Zijlstra
2022-10-14 15:52 ` Edgecombe, Rick P
2022-10-14 9:42 ` Peter Zijlstra
2022-10-14 18:06 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 11/39] x86/mm: Update pte_modify for _PAGE_COW Rick Edgecombe
2022-09-29 22:29 ` [PATCH v2 12/39] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Rick Edgecombe
2022-10-03 17:43 ` Kirill A . Shutemov
2022-10-03 18:11 ` Nadav Amit
2022-10-03 18:51 ` Dave Hansen
2022-10-03 22:28 ` Edgecombe, Rick P
2022-10-03 23:17 ` Nadav Amit
2022-10-03 23:20 ` Nadav Amit
2022-10-03 23:25 ` Nadav Amit
2022-10-03 23:38 ` Edgecombe, Rick P
2022-10-04 0:40 ` Nadav Amit
2022-09-29 22:29 ` [PATCH v2 13/39] mm: Move VM_UFFD_MINOR_BIT from 37 to 38 Rick Edgecombe
2022-10-03 18:11 ` Kees Cook
2022-10-03 18:24 ` Peter Xu
2022-09-29 22:29 ` [PATCH v2 14/39] mm: Introduce VM_SHADOW_STACK for shadow stack memory Rick Edgecombe
2022-10-03 17:47 ` Kirill A . Shutemov
2022-10-04 0:29 ` Edgecombe, Rick P
2022-10-03 18:17 ` Kees Cook
2022-09-29 22:29 ` [PATCH v2 15/39] x86/mm: Check Shadow Stack page fault errors Rick Edgecombe
2022-10-03 18:20 ` Kees Cook
2022-10-14 10:07 ` Peter Zijlstra
2022-10-14 15:51 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 16/39] x86/mm: Update maybe_mkwrite() for shadow stack Rick Edgecombe
2022-10-03 18:22 ` Kees Cook
2022-10-03 23:53 ` Kirill A . Shutemov
2022-10-14 15:32 ` Peter Zijlstra
2022-10-14 15:45 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 17/39] mm: Fixup places that call pte_mkwrite() directly Rick Edgecombe
2022-10-03 18:24 ` Kees Cook
2022-10-03 23:56 ` Kirill A . Shutemov
2022-10-04 16:15 ` Edgecombe, Rick P
2022-10-04 1:56 ` Nadav Amit
2022-10-04 16:21 ` Edgecombe, Rick P
2022-10-14 15:52 ` Peter Zijlstra
2022-10-14 15:56 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 18/39] mm: Add guard pages around a shadow stack Rick Edgecombe
2022-10-03 18:30 ` Kees Cook
2022-10-05 2:30 ` Andrew Cooper
2022-10-10 12:33 ` Florian Weimer
2022-10-10 13:32 ` Andrew Cooper
2022-10-10 13:40 ` Florian Weimer
2022-10-10 13:56 ` Andrew Cooper
2022-09-29 22:29 ` [PATCH v2 19/39] mm/mmap: Add shadow stack pages to memory accounting Rick Edgecombe
2022-10-03 18:31 ` Kees Cook
2022-10-04 0:03 ` Kirill A . Shutemov
2022-10-04 0:32 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 20/39] mm/mprotect: Exclude shadow stack from preserve_write Rick Edgecombe
2022-09-29 22:29 ` [PATCH v2 21/39] mm: Re-introduce vm_flags to do_mmap() Rick Edgecombe
2022-09-29 22:29 ` [PATCH v2 22/39] mm: Don't allow write GUPs to shadow stack memory Rick Edgecombe
2022-09-30 19:16 ` Dave Hansen
2022-09-30 20:30 ` Edgecombe, Rick P
2022-09-30 20:37 ` Dave Hansen
2022-09-30 23:00 ` Jann Horn
2022-09-30 23:02 ` Jann Horn
2022-09-30 23:04 ` Edgecombe, Rick P
2022-10-03 18:39 ` Kees Cook
2022-10-03 22:49 ` Andy Lutomirski
2022-10-04 4:21 ` Kees Cook
2022-09-29 22:29 ` [PATCH v2 23/39] x86: Introduce userspace API for CET enabling Rick Edgecombe
2022-10-03 19:01 ` Kees Cook
2022-10-03 22:51 ` Edgecombe, Rick P
2022-10-06 18:50 ` Mike Rapoport
2022-10-10 10:56 ` Florian Weimer
2022-10-10 16:28 ` Edgecombe, Rick P
2022-10-12 12:18 ` Florian Weimer
2022-10-12 17:30 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 24/39] x86/cet/shstk: Add user-mode shadow stack support Rick Edgecombe
2022-10-03 19:43 ` Kees Cook
2022-10-03 20:04 ` Dave Hansen
2022-10-04 4:04 ` Kees Cook
2022-10-04 16:25 ` Edgecombe, Rick P
2022-10-04 10:17 ` David Laight
2022-10-04 19:32 ` Kees Cook
2022-10-05 13:32 ` David Laight
2022-10-20 21:29 ` Edgecombe, Rick P
2022-10-20 22:54 ` Kees Cook
2022-09-29 22:29 ` [PATCH v2 25/39] x86/cet/shstk: Handle thread shadow stack Rick Edgecombe
2022-10-03 10:36 ` Mike Rapoport
2022-10-03 16:57 ` Edgecombe, Rick P
2022-10-03 20:29 ` Kees Cook
2022-10-04 22:09 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 26/39] x86/cet/shstk: Introduce routines modifying shstk Rick Edgecombe
2022-10-03 20:44 ` Kees Cook
2022-10-04 22:13 ` Edgecombe, Rick P
2022-10-05 2:43 ` Andrew Cooper
2022-10-05 22:47 ` Edgecombe, Rick P
2022-10-05 22:58 ` Andrew Cooper
2022-10-20 21:51 ` Edgecombe, Rick P
2022-09-29 22:29 ` [PATCH v2 27/39] x86/cet/shstk: Handle signals for shadow stack Rick Edgecombe
2022-10-03 20:52 ` Kees Cook
2022-10-20 22:08 ` Edgecombe, Rick P
2022-10-20 22:57 ` Kees Cook
2022-09-29 22:29 ` [PATCH v2 28/39] x86/cet/shstk: Introduce map_shadow_stack syscall Rick Edgecombe
2022-10-03 22:23 ` Kees Cook
2022-10-04 22:56 ` Edgecombe, Rick P
2022-10-04 23:16 ` H.J. Lu
2022-10-10 11:13 ` Florian Weimer
2022-10-10 14:19 ` Jason A. Donenfeld
2022-09-29 22:29 ` [PATCH v2 29/39] x86/cet/shstk: Support wrss for userspace Rick Edgecombe
2022-10-03 22:28 ` Kees Cook
2022-10-03 23:00 ` Andy Lutomirski
2022-10-04 4:37 ` Kees Cook
2022-10-06 0:38 ` Edgecombe, Rick P
2022-10-06 3:11 ` Kees Cook
2022-10-04 8:30 ` Mike Rapoport
2022-09-29 22:29 ` [PATCH v2 30/39] x86: Expose thread features status in /proc/$PID/arch_status Rick Edgecombe
2022-10-03 22:37 ` Kees Cook
2022-10-03 22:45 ` Andy Lutomirski
2022-10-04 4:18 ` Kees Cook
2022-09-29 22:29 ` [PATCH v2 31/39] x86/cet/shstk: Wire in CET interface Rick Edgecombe
2022-10-03 22:41 ` Kees Cook
2022-09-29 22:29 ` [PATCH v2 32/39] selftests/x86: Add shadow stack test Rick Edgecombe
2022-10-03 23:56 ` Kees Cook
2022-09-29 22:29 ` [PATCH v2 33/39] x86/cpufeatures: Limit shadow stack to Intel CPUs Rick Edgecombe
2022-10-03 23:57 ` Kees Cook
2022-10-04 0:09 ` Dave Hansen
2022-10-04 4:54 ` Kees Cook
2022-10-04 15:47 ` Nathan Chancellor
2022-10-04 19:43 ` John Allen
2022-10-04 20:34 ` Edgecombe, Rick P
2022-10-04 20:50 ` Nathan Chancellor
2022-10-04 21:17 ` H. Peter Anvin
2022-10-04 23:24 ` Edgecombe, Rick P
2022-11-03 17:39 ` John Allen
2022-10-20 21:22 ` Edgecombe, Rick P
2022-10-04 8:36 ` Mike Rapoport
2022-09-29 22:29 ` [OPTIONAL/CLEANUP v2 34/39] x86: Separate out x86_regset for 32 and 64 bit Rick Edgecombe
2022-09-29 22:29 ` [OPTIONAL/CLEANUP v2 35/39] x86: Improve formatting of user_regset arrays Rick Edgecombe
2022-09-29 22:29 ` [OPTIONAL/RFC v2 36/39] x86/fpu: Add helper for initing features Rick Edgecombe
2022-10-03 19:07 ` Chang S. Bae
2022-10-04 23:05 ` Edgecombe, Rick P
2022-09-29 22:29 ` [OPTIONAL/RFC v2 37/39] x86/cet: Add PTRACE interface for CET Rick Edgecombe
2022-10-03 23:59 ` Kees Cook
2022-10-04 8:44 ` Mike Rapoport
2022-10-04 19:24 ` Kees Cook
2022-09-29 22:29 ` [OPTIONAL/RFC v2 38/39] x86/cet/shstk: Add ARCH_CET_UNLOCK Rick Edgecombe
2022-10-04 0:00 ` Kees Cook
2022-09-29 22:29 ` [OPTIONAL/RFC v2 39/39] x86: Add alt shadow stack support Rick Edgecombe
2022-10-03 23:21 ` Andy Lutomirski
2022-10-04 16:12 ` Edgecombe, Rick P
2022-10-04 17:46 ` Andy Lutomirski
2022-10-04 18:04 ` Edgecombe, Rick P
2022-10-03 17:04 ` [PATCH v2 00/39] Shadowstacks for userspace Kees Cook
2022-10-03 17:25 ` Jann Horn
2022-10-04 5:01 ` Kees Cook [this message]
2022-10-04 9:57 ` David Laight
2022-10-04 19:28 ` Kees Cook
2022-10-03 18:33 ` Edgecombe, Rick P
2022-10-04 3:59 ` Kees Cook
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