From: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
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Cc: "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Subject: Re: [PATCH v5 10/39] x86/mm: Introduce _PAGE_COW
Date: Mon, 23 Jan 2023 20:56:36 +0000 [thread overview]
Message-ID: <bbc4f4df98ec798ae15e5daa6b5ceab41bcc66f9.camel@intel.com> (raw)
In-Reply-To: <634aa365-1f51-8684-24ae-3b68aba1e12a@redhat.com>
Trying to answer both questions to this patch on this one.
On Mon, 2023-01-23 at 10:28 +0100, David Hildenbrand wrote:
> > +/*
> > + * Normally COW memory can result in Dirty=1,Write=0 PTEs. But in
> > the case
> > + * of X86_FEATURE_USER_SHSTK, the software COW bit is used, since
> > the
> > + * Dirty=1,Write=0 will result in the memory being treated as
> > shadow stack
> > + * by the HW. So when creating COW memory, a software bit is used
> > + * _PAGE_BIT_COW. The following functions pte_mkcow() and
> > pte_clear_cow()
> > + * take a PTE marked conventionally COW (Dirty=1) and transition
> > it to the
> > + * shadow stack compatible version of COW (Cow=1).
> > + */
>
> TBH, I find that all highly confusing.
>
> Dirty=1,Write=0 does not indicate a COW page reliably. You could
> have
> both, false negatives and false positives.
>
> False negative: fork() on a clean anon page.
>
> False positives: wrpotect() of a dirty anon page.
>
>
> I wonder if it really has to be that complicated: what you really
> want
> to achieve is to disallow "Dirty=1,Write=0" if it's not a shadow
> stack
> page, correct?
The other thing is to save that the PTE is/was Dirty=1 somewhere (for
non-shadow stack memory). A slightly different but related thing. But
losing that information would would introduce differences for
pte_dirty() between when shadow stack was enabled or not. GUP/COW
doesn't need this anymore but there are lots of other places it gets
checked.
Perhaps following your GUP changes, _PAGE_COW is just now the wrong
name for it. _PAGE_SAVED_DIRTY maybe?
next prev parent reply other threads:[~2023-01-23 20:57 UTC|newest]
Thread overview: 120+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-19 21:22 [PATCH v5 00/39] Shadow stacks for userspace Rick Edgecombe
2023-01-19 21:22 ` [PATCH v5 01/39] Documentation/x86: Add CET shadow stack description Rick Edgecombe
2023-01-20 0:38 ` Kees Cook
2023-01-19 21:22 ` [PATCH v5 02/39] x86/shstk: Add Kconfig option for shadow stack Rick Edgecombe
2023-01-20 0:40 ` Kees Cook
2023-01-19 21:22 ` [PATCH v5 03/39] x86/cpufeatures: Add CPU feature flags for shadow stacks Rick Edgecombe
2023-01-20 0:44 ` Kees Cook
2023-01-19 21:22 ` [PATCH v5 04/39] x86/cpufeatures: Enable CET CR4 bit for shadow stack Rick Edgecombe
2023-01-20 0:46 ` Kees Cook
2023-01-19 21:22 ` [PATCH v5 05/39] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Rick Edgecombe
2023-01-20 0:46 ` Kees Cook
2023-01-19 21:22 ` [PATCH v5 06/39] x86/fpu: Add helper for modifying xstate Rick Edgecombe
2023-01-20 0:47 ` Kees Cook
2023-02-01 11:01 ` Borislav Petkov
2023-02-01 17:31 ` Edgecombe, Rick P
2023-02-01 18:18 ` Borislav Petkov
2023-01-19 21:22 ` [PATCH v5 07/39] x86: Add user control-protection fault handler Rick Edgecombe
2023-01-20 0:50 ` Kees Cook
2023-02-03 19:09 ` Borislav Petkov
2023-02-03 19:24 ` Edgecombe, Rick P
2023-02-03 19:44 ` Borislav Petkov
2023-02-03 23:01 ` Edgecombe, Rick P
2023-02-04 10:37 ` Borislav Petkov
2023-01-19 21:22 ` [PATCH v5 08/39] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Rick Edgecombe
2023-01-20 0:52 ` Kees Cook
2023-01-19 21:22 ` [PATCH v5 09/39] x86/mm: Move pmd_write(), pud_write() up in the file Rick Edgecombe
2023-01-19 21:22 ` [PATCH v5 10/39] x86/mm: Introduce _PAGE_COW Rick Edgecombe
2023-01-20 0:55 ` Kees Cook
2023-01-23 9:16 ` David Hildenbrand
2023-01-23 9:28 ` David Hildenbrand
2023-01-23 20:56 ` Edgecombe, Rick P [this message]
2023-01-24 16:28 ` David Hildenbrand
2023-01-19 21:22 ` [PATCH v5 11/39] x86/mm: Update pte_modify for _PAGE_COW Rick Edgecombe
2023-01-20 0:57 ` Kees Cook
2023-02-09 14:08 ` Borislav Petkov
2023-02-09 17:09 ` Edgecombe, Rick P
2023-02-10 13:57 ` Borislav Petkov
2023-02-10 17:00 ` Edgecombe, Rick P
2023-02-17 16:11 ` Borislav Petkov
2023-02-17 16:53 ` Edgecombe, Rick P
2023-01-19 21:22 ` [PATCH v5 12/39] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Rick Edgecombe
2023-01-20 0:58 ` Kees Cook
2023-01-19 21:22 ` [PATCH v5 13/39] x86/mm: Start actually marking _PAGE_COW Rick Edgecombe
2023-01-19 21:22 ` [PATCH v5 14/39] mm: Move VM_UFFD_MINOR_BIT from 37 to 38 Rick Edgecombe
2023-01-19 21:22 ` [PATCH v5 15/39] mm: Introduce VM_SHADOW_STACK for shadow stack memory Rick Edgecombe
2023-01-19 21:22 ` [PATCH v5 16/39] x86/mm: Check shadow stack page fault errors Rick Edgecombe
2023-01-20 0:59 ` Kees Cook
2023-01-19 21:22 ` [PATCH v5 17/39] x86/mm: Update maybe_mkwrite() for shadow stack Rick Edgecombe
2023-01-19 21:22 ` [PATCH v5 18/39] mm: Handle faultless write upgrades for shstk Rick Edgecombe
2023-01-23 9:50 ` David Hildenbrand
2023-01-23 20:47 ` Edgecombe, Rick P
2023-01-24 16:24 ` David Hildenbrand
2023-01-24 18:14 ` Edgecombe, Rick P
2023-01-25 9:27 ` David Hildenbrand
2023-01-25 18:43 ` Edgecombe, Rick P
2023-01-26 0:59 ` Edgecombe, Rick P
2023-01-26 8:46 ` David Hildenbrand
2023-01-26 20:19 ` Edgecombe, Rick P
2023-01-27 16:12 ` David Hildenbrand
2023-01-28 0:51 ` Edgecombe, Rick P
2023-01-31 8:46 ` David Hildenbrand
2023-01-31 23:33 ` Edgecombe, Rick P
2023-02-01 9:03 ` David Hildenbrand
2023-02-01 17:32 ` Edgecombe, Rick P
2023-02-01 18:03 ` David Hildenbrand
2023-01-26 8:57 ` David Hildenbrand
2023-01-26 20:16 ` Edgecombe, Rick P
2023-01-27 16:19 ` David Hildenbrand
2023-01-19 21:22 ` [PATCH v5 19/39] mm: Fixup places that call pte_mkwrite() directly Rick Edgecombe
2023-01-20 1:01 ` Kees Cook
2023-02-14 0:09 ` Deepak Gupta
2023-02-14 1:07 ` Edgecombe, Rick P
2023-02-14 6:10 ` Deepak Gupta
2023-02-14 18:24 ` Edgecombe, Rick P
2023-02-15 6:37 ` Deepak Gupta
2023-01-19 21:22 ` [PATCH v5 20/39] mm: Add guard pages around a shadow stack Rick Edgecombe
2023-01-19 21:22 ` [PATCH v5 21/39] mm/mmap: Add shadow stack pages to memory accounting Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 22/39] mm: Re-introduce vm_flags to do_mmap() Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 23/39] mm: Don't allow write GUPs to shadow stack memory Rick Edgecombe
2023-01-23 9:10 ` David Hildenbrand
2023-01-23 10:45 ` Florian Weimer
2023-01-23 20:46 ` Edgecombe, Rick P
2023-01-24 16:26 ` David Hildenbrand
2023-01-24 18:42 ` Edgecombe, Rick P
2023-01-24 23:08 ` Kees Cook
2023-01-24 23:41 ` Edgecombe, Rick P
2023-01-25 9:29 ` David Hildenbrand
2023-01-25 15:23 ` Kees Cook
2023-01-25 15:36 ` Schimpe, Christina
2023-01-25 16:43 ` Schimpe, Christina
2023-01-19 21:23 ` [PATCH v5 24/39] x86/mm: Introduce MAP_ABOVE4G Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 25/39] mm: Warn on shadow stack memory in wrong vma Rick Edgecombe
2023-01-20 1:01 ` Kees Cook
2023-01-19 21:23 ` [PATCH v5 26/39] x86: Introduce userspace API for shadow stack Rick Edgecombe
2023-01-20 1:04 ` Kees Cook
2023-01-19 21:23 ` [PATCH v5 27/39] x86/shstk: Add user-mode shadow stack support Rick Edgecombe
2023-01-20 1:05 ` Kees Cook
2023-01-19 21:23 ` [PATCH v5 28/39] x86/shstk: Handle thread shadow stack Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 29/39] x86/shstk: Introduce routines modifying shstk Rick Edgecombe
2023-01-20 1:05 ` Kees Cook
2023-01-19 21:23 ` [PATCH v5 30/39] x86/shstk: Handle signals for shadow stack Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 31/39] x86/shstk: Introduce map_shadow_stack syscall Rick Edgecombe
2023-01-20 1:07 ` Kees Cook
2023-01-19 21:23 ` [PATCH v5 32/39] x86/shstk: Support WRSS for userspace Rick Edgecombe
2023-01-20 1:06 ` Kees Cook
2023-01-19 21:23 ` [PATCH v5 33/39] x86: Expose thread features in /proc/$PID/status Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 34/39] x86/shstk: Wire in shadow stack interface Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 35/39] selftests/x86: Add shadow stack test Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 36/39] x86/fpu: Add helper for initing features Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 37/39] x86: Add PTRACE interface for shadow stack Rick Edgecombe
2023-01-20 1:08 ` Kees Cook
2023-01-19 21:23 ` [PATCH v5 38/39] x86/shstk: Add ARCH_SHSTK_UNLOCK Rick Edgecombe
2023-01-19 21:23 ` [PATCH v5 39/39] x86/shstk: Add ARCH_SHSTK_STATUS Rick Edgecombe
2023-01-20 1:08 ` Kees Cook
2023-01-19 22:26 ` [PATCH v5 00/39] Shadow stacks for userspace Andrew Morton
2023-01-20 17:27 ` Edgecombe, Rick P
2023-01-20 19:19 ` Kees Cook
2023-01-25 19:46 ` Edgecombe, Rick P
2023-01-20 17:48 ` John Allen
2023-01-22 8:20 ` Mike Rapoport
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