From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: 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>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
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>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
Dave Martin <Dave.Martin@arm.com>,
Weijiang Yang <weijiang.yang@intel.com>,
Pengfei Xu <pengfei.xu@intel.com>,
Haitao Huang <haitao.huang@intel.com>
Subject: Re: [PATCH v23 09/28] x86/mm: Introduce _PAGE_COW
Date: Mon, 22 Mar 2021 14:29:51 +0300 [thread overview]
Message-ID: <20210322112951.6mqjgxmkafmiavpb@box> (raw)
In-Reply-To: <20210316151054.5405-10-yu-cheng.yu@intel.com>
On Tue, Mar 16, 2021 at 08:10:35AM -0700, Yu-cheng Yu wrote:
> There is essentially no room left in the x86 hardware PTEs on some OSes
> (not Linux). That left the hardware architects looking for a way to
> represent a new memory type (shadow stack) within the existing bits.
> They chose to repurpose a lightly-used state: Write=0, Dirty=1.
>
> The reason it's lightly used is that Dirty=1 is normally set by hardware
> and cannot normally be set by hardware on a Write=0 PTE. Software must
> normally be involved to create one of these PTEs, so software can simply
> opt to not create them.
>
> In places where Linux normally creates Write=0, Dirty=1, it can use the
> software-defined _PAGE_COW in place of the hardware _PAGE_DIRTY. In other
> words, whenever Linux needs to create Write=0, Dirty=1, it instead creates
> Write=0, Cow=1, except for shadow stack, which is Write=0, Dirty=1. This
> clearly separates shadow stack from other data, and results in the
> following:
>
> (a) A modified, copy-on-write (COW) page: (Write=0, Cow=1)
> (b) A R/O page that has been COW'ed: (Write=0, Cow=1)
> The user page is in a R/O VMA, and get_user_pages() needs a writable
> copy. The page fault handler creates a copy of the page and sets
> the new copy's PTE as Write=0 and Cow=1.
> (c) A shadow stack PTE: (Write=0, Dirty=1)
> (d) A shared shadow stack PTE: (Write=0, Cow=1)
> When a shadow stack page is being shared among processes (this happens
> at fork()), its PTE is made Dirty=0, so the next shadow stack access
> causes a fault, and the page is duplicated and Dirty=1 is set again.
> This is the COW equivalent for shadow stack pages, even though it's
> copy-on-access rather than copy-on-write.
> (e) A page where the processor observed a Write=1 PTE, started a write, set
> Dirty=1, but then observed a Write=0 PTE. That's possible today, but
> will not happen on processors that support shadow stack.
>
> Define _PAGE_COW and update pte_*() helpers and apply the same changes to
> pmd and pud.
>
> After this, there are six free bits left in the 64-bit PTE, and no more
> free bits in the 32-bit PTE (except for PAE) and Shadow Stack is not
> implemented for the 32-bit kernel.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
--
Kirill A. Shutemov
next prev parent reply other threads:[~2021-03-22 11:30 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 15:10 [PATCH v23 00/28] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 01/28] Documentation/x86: Add CET description Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 02/28] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 03/28] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 04/28] x86/cpufeatures: Introduce X86_FEATURE_CET and setup functions Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 05/28] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 06/28] x86/cet: Add control-protection fault handler Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 07/28] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Yu-cheng Yu
2021-03-22 9:13 ` Kirill A. Shutemov
2021-03-22 14:52 ` Yu, Yu-cheng
2021-03-16 15:10 ` [PATCH v23 08/28] x86/mm: Move pmd_write(), pud_write() up in the file Yu-cheng Yu
2021-03-22 11:28 ` Kirill A. Shutemov
2021-03-16 15:10 ` [PATCH v23 09/28] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2021-03-22 11:29 ` Kirill A. Shutemov [this message]
2021-03-16 15:10 ` [PATCH v23 10/28] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2021-03-22 11:30 ` Kirill A. Shutemov
2021-03-16 15:10 ` [PATCH v23 11/28] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2021-03-22 11:31 ` Kirill A. Shutemov
2021-03-16 15:10 ` [PATCH v23 12/28] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Yu-cheng Yu
2021-03-22 10:15 ` Kirill A. Shutemov
2021-03-22 10:46 ` Peter Zijlstra
2021-03-22 11:38 ` Kirill A. Shutemov
2021-03-16 15:10 ` [PATCH v23 13/28] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2021-03-22 11:33 ` Kirill A. Shutemov
2021-03-16 15:10 ` [PATCH v23 14/28] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2021-03-22 10:38 ` Kirill A. Shutemov
2021-03-22 17:27 ` Yu, Yu-cheng
2021-03-16 15:10 ` [PATCH v23 15/28] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2021-03-17 15:56 ` Borislav Petkov
2021-03-22 10:46 ` Kirill A. Shutemov
2021-03-16 15:10 ` [PATCH v23 16/28] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2021-03-18 9:47 ` Borislav Petkov
2021-03-18 11:16 ` Borislav Petkov
2021-03-16 15:10 ` [PATCH v23 17/28] mm: Add guard pages around a shadow stack Yu-cheng Yu
2021-03-22 10:55 ` Kirill A. Shutemov
2021-03-16 15:10 ` [PATCH v23 18/28] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2021-03-22 10:57 ` Kirill A. Shutemov
2021-03-26 15:46 ` Yu, Yu-cheng
2021-03-29 10:10 ` Kirill A. Shutemov
2021-03-16 15:10 ` [PATCH v23 19/28] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 20/28] mm/mprotect: Exclude shadow stack from preserve_write Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 21/28] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2021-03-18 11:42 ` Borislav Petkov
2021-03-18 15:59 ` Yu, Yu-cheng
2021-03-18 16:13 ` Borislav Petkov
2021-03-16 15:10 ` [PATCH v23 22/28] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu
2021-03-18 12:32 ` Borislav Petkov
2021-03-18 19:05 ` Yu, Yu-cheng
2021-03-19 9:28 ` Borislav Petkov
2021-03-19 15:15 ` Yu, Yu-cheng
2021-03-16 15:10 ` [PATCH v23 23/28] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2021-03-19 12:51 ` Borislav Petkov
2021-03-16 15:10 ` [PATCH v23 24/28] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 25/28] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 26/28] x86/cet/shstk: Add arch_prctl functions for " Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 27/28] mm: Move arch_calc_vm_prot_bits() to arch/x86/include/asm/mman.h Yu-cheng Yu
2021-03-16 15:10 ` [PATCH v23 28/28] mm: Introduce PROT_SHSTK for shadow stack Yu-cheng Yu
2021-03-22 11:27 ` Kirill A. Shutemov
2021-03-16 21:15 ` [PATCH v23 00/28] Control-flow Enforcement: Shadow Stack Peter Zijlstra
2021-03-16 21:34 ` Yu, Yu-cheng
2021-03-17 9:18 ` Ingo Molnar
2021-03-17 10:14 ` Peter Zijlstra
2021-03-19 16:24 ` Yu, Yu-cheng
2021-03-19 21:43 ` Yu, Yu-cheng
2021-03-23 20:49 ` Peter Zijlstra
2021-03-23 21:03 ` Yu, Yu-cheng
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