From: Randy Dunlap <rdunlap@infradead.org>
To: Yu-cheng Yu <yu-cheng.yu@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>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Mike Kravetz <mike.kravetz@oracle.com>
Subject: Re: [RFC PATCH v9 01/27] Documentation/x86: Add CET description
Date: Wed, 5 Feb 2020 16:16:05 -0800 [thread overview]
Message-ID: <af5ee976-3b57-4afe-6304-fcab8de45c77@infradead.org> (raw)
In-Reply-To: <20200205181935.3712-2-yu-cheng.yu@intel.com>
Hi,
I have a few comments and a question (please see inline below).
On 2/5/20 10:19 AM, Yu-cheng Yu wrote:
> Explain no_cet_shstk/no_cet_ibt kernel parameters, and introduce a new
> document on Control-flow Enforcement Technology (CET).
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> ---
> .../admin-guide/kernel-parameters.txt | 6 +
> Documentation/x86/index.rst | 1 +
> Documentation/x86/intel_cet.rst | 294 ++++++++++++++++++
> 3 files changed, 301 insertions(+)
> create mode 100644 Documentation/x86/intel_cet.rst
>
> diff --git a/Documentation/x86/intel_cet.rst b/Documentation/x86/intel_cet.rst
> new file mode 100644
> index 000000000000..71e2462fea5c
> --- /dev/null
> +++ b/Documentation/x86/intel_cet.rst
> @@ -0,0 +1,294 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=========================================
> +Control-flow Enforcement Technology (CET)
> +=========================================
> +
...
> +
> +[5] CET system calls
> +====================
> +
> +The following arch_prctl() system calls are added for CET:
> +
> +arch_prctl(ARCH_X86_CET_STATUS, unsigned long *addr)
> + Return CET feature status.
> +
> + The parameter 'addr' is a pointer to a user buffer.
> + On returning to the caller, the kernel fills the following
> + information::
> +
> + *addr = SHSTK/IBT status
> + *(addr + 1) = SHSTK base address
> + *(addr + 2) = SHSTK size
> +
> +arch_prctl(ARCH_X86_CET_DISABLE, unsigned long features)
> + Disable SHSTK and/or IBT specified in 'features'. Return -EPERM
> + if CET is locked.
> +
> +arch_prctl(ARCH_X86_CET_LOCK)
> + Lock in CET feature.
which feature?
> +
> +arch_prctl(ARCH_X86_CET_ALLOC_SHSTK, unsigned long *addr)
> + Allocate a new SHSTK and put a restore token at top.
> +
> + The parameter 'addr' is a pointer to a user buffer and indicates
> + the desired SHSTK size to allocate. On returning to the caller,
> + the kernel fills '*addr' with the base address of the new SHSTK.
> +
> +arch_prctl(ARCH_X86_CET_MARK_LEGACY_CODE, unsigned long *addr)
> + Mark an address range as IBT legacy code.
> +
> + The parameter 'addr' is a pointer to a user buffer that has the
> + following information::
> +
> + *addr = starting linear address of the legacy code
> + *(addr + 1) = size of the legacy code
> + *(addr + 2) = set (1); clear (0)
> +
> +Note:
> + There is no CET-enabling arch_prctl function. By design, CET is
> + enabled automatically if the binary and the system can support it.
> +
> + The parameters passed are always unsigned 64-bit. When an IA32
> + application passing pointers, it should only use the lower 32 bits.
> +
> +[6] The implementation of the SHSTK
> +===================================
> +
> +SHSTK size
> +----------
> +
> +A task's SHSTK is allocated from memory to a fixed size of
> +RLIMIT_STACK. A compat-mode thread's SHSTK size is 1/4 of
> +RLIMIT_STACK. The smaller 32-bit thread SHSTK allows more threads to
> +share a 32-bit address space.
> +
> +Signal
> +------
> +
> +The main program and its signal handlers use the same SHSTK. Because
> +the SHSTK stores only return addresses, a large SHSTK will cover the
> +condition that both the program stack and the sigaltstack run out.
> +
> +The kernel creates a restore token at the SHSTK restoring address and
> +verifies that token when restoring from the signal handler.
> +
> +IBT for signal delivering and sigreturn is the same as the main
> +program's setup; except for WAIT_ENDBR status, which can be read from
s/;/,/
> +MSR_IA32_U_CET. In general, a task is in WAIT_ENDBR after an
> +indirect CALL/JMP and before the next instruction starts.
> +
> +A task's WAIT_ENDBR is reset for its signal handler, but preserved on
> +the task's stack; and then restored from sigreturn.
s/;/,/
> +
> +Fork
> +----
> +
> +The SHSTK's vma has VM_SHSTK flag set; its PTEs are required to be
> +read-only and dirty. When a SHSTK PTE is not present, RO, and dirty,
> +a SHSTK access triggers a page fault with an additional SHSTK bit set
> +in the page fault error code.
> +
> +When a task forks a child, its SHSTK PTEs are copied and both the
> +parent's and the child's SHSTK PTEs are cleared of the dirty bit.
> +Upon the next SHSTK access, the resulting SHSTK page fault is handled
> +by page copy/re-use.
> +
> +When a pthread child is created, the kernel allocates a new SHSTK for
> +the new thread.
> +
> +Setjmp/Longjmp
> +--------------
> +
> +Longjmp unwinds SHSTK until it matches the program stack.
> +
> +Ucontext
> +--------
> +
> +In GLIBC, getcontext/setcontext is implemented in similar way as
> +setjmp/longjmp.
> +
> +When makecontext creates a new ucontext, a new SHSTK is allocated for
> +that context with ARCH_X86_CET_ALLOC_SHSTK syscall. The kernel
> +creates a restore token at the top of the new SHSTK and the user-mode
> +code switches to the new SHSTK with the RSTORSSP instruction.
> +
> +[7] The management of read-only & dirty PTEs for SHSTK
> +======================================================
> +
> +A RO and dirty PTE exists in the following cases:
> +
> +(a) A page is modified and then shared with a fork()'ed child;
> +(b) A R/O page that has been COW'ed;
> +(c) A SHSTK page.
> +
> +The processor only checks the dirty bit for (c). To prevent the use
> +of non-SHSTK memory as SHSTK, we use a spare bit of the 64-bit PTE as
> +DIRTY_SW for (a) and (b) above. This results to the following PTE
> +settings::
> +
> + Modified PTE: (R/W + DIRTY_HW)
> + Modified and shared PTE: (R/O + DIRTY_SW)
> + R/O PTE, COW'ed: (R/O + DIRTY_SW)
> + SHSTK PTE: (R/O + DIRTY_HW)
> + SHSTK PTE, COW'ed: (R/O + DIRTY_HW)
> + SHSTK PTE, shared: (R/O + DIRTY_SW)
> +
> +Note that DIRTY_SW is only used in R/O PTEs but not R/W PTEs.
> +
> +[8] The implementation of IBT legacy bitmap
> +===========================================
> +
> +When IBT is active, a non-IBT-capable legacy library can be executed
> +if its address ranges are specified in the legacy code bitmap. The
> +bitmap covers the whole user-space address, which is TASK_SIZE_MAX
> +for 64-bit and TASK_SIZE for IA32, and its each bit indicates a 4-KB
confusing:
its each bit
> +legacy code page. It is read-only from an application, and setup by
> +the kernel as a special mapping when the first time the application
drop: when
> +calls arch_prctl(ARCH_X86_CET_MARK_LEGACY_CODE). The application
> +manages the bitmap through the arch_prctl.
through the arch_prctl() interface.
cheers.
--
~Randy
next prev parent reply other threads:[~2020-02-06 0:16 UTC|newest]
Thread overview: 107+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 18:19 [RFC PATCH v9 00/27] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 01/27] Documentation/x86: Add CET description Yu-cheng Yu
2020-02-06 0:16 ` Randy Dunlap [this message]
[not found] ` <af5ee976-3b57-4afe-6304-fcab8de45c77-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2020-02-06 20:17 ` Yu-cheng Yu
2020-02-25 20:02 ` Kees Cook
2020-02-28 15:55 ` Yu-cheng Yu
2020-02-26 17:57 ` Dave Hansen
2020-03-09 17:00 ` Yu-cheng Yu
2020-03-09 17:21 ` Dave Hansen
2020-03-09 19:27 ` Yu-cheng Yu
2020-03-09 19:35 ` Dave Hansen
2020-03-09 19:50 ` H.J. Lu
2020-03-09 20:16 ` Andy Lutomirski
2020-03-09 20:54 ` H.J. Lu
2020-03-09 20:59 ` Dave Hansen
2020-03-09 21:12 ` H.J. Lu
2020-03-09 22:02 ` Andy Lutomirski
2020-03-09 22:19 ` Dave Hansen
2020-03-09 23:11 ` H.J. Lu
2020-03-09 23:20 ` Dave Hansen
2020-03-09 23:51 ` H.J. Lu
2020-03-09 23:59 ` Andy Lutomirski
2020-03-10 0:08 ` H.J. Lu
2020-03-10 1:21 ` Andy Lutomirski
2020-03-10 2:13 ` H.J. Lu
2020-02-05 18:19 ` [RFC PATCH v9 03/27] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-02-25 20:04 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 04/27] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-02-25 20:06 ` Kees Cook
2020-02-26 17:10 ` Dave Hansen
2020-03-05 20:44 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 06/27] mm: Introduce VM_SHSTK for Shadow Stack memory Yu-cheng Yu
2020-02-25 20:07 ` Kees Cook
2020-02-26 18:07 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 07/27] Add guard pages around a Shadow Stack Yu-cheng Yu
2020-02-25 20:11 ` Kees Cook
2020-02-26 18:17 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 08/27] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-02-25 20:12 ` Kees Cook
2020-02-26 18:20 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 10/27] x86/mm: Update pte_modify, pmd_modify, and _PAGE_CHG_MASK for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-26 22:02 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 11/27] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-02-25 20:13 ` Kees Cook
2020-02-26 22:04 ` Dave Hansen
2020-04-03 15:42 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 13/27] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-02-25 20:16 ` Kees Cook
2020-02-26 22:47 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 14/27] mm: Handle Shadow Stack page fault Yu-cheng Yu
2020-02-25 20:20 ` Kees Cook
2020-03-05 18:30 ` Yu-cheng Yu
2020-02-27 0:08 ` Dave Hansen
2020-04-07 18:14 ` Yu-cheng Yu
2020-04-07 22:21 ` Dave Hansen
2020-04-08 18:18 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 15/27] mm: Handle THP/HugeTLB " Yu-cheng Yu
2020-02-25 20:59 ` Kees Cook
2020-03-13 22:00 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 16/27] mm: Update can_follow_write_pte() for Shadow Stack Yu-cheng Yu
2020-02-27 0:34 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 17/27] x86/cet/shstk: User-mode Shadow Stack support Yu-cheng Yu
2020-02-25 21:07 ` Kees Cook
2020-02-27 0:55 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 18/27] x86/cet/shstk: Introduce WRUSS instruction Yu-cheng Yu
2020-02-25 21:10 ` Kees Cook
2020-03-05 18:39 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 19/27] x86/cet/shstk: Handle signals for Shadow Stack Yu-cheng Yu
2020-02-25 21:17 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 20/27] ELF: UAPI and Kconfig additions for ELF program properties Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 22/27] ELF: Add ELF program property parsing support Yu-cheng Yu
2020-02-25 21:20 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 23/27] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 24/27] x86/cet/shstk: ELF header parsing for Shadow Stack Yu-cheng Yu
2020-02-25 21:22 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 25/27] x86/cet/shstk: Handle thread " Yu-cheng Yu
2020-02-25 21:29 ` Kees Cook
2020-03-25 21:51 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 26/27] mm/mmap: Add Shadow Stack pages to memory accounting Yu-cheng Yu
[not found] ` <20200205181935.3712-1-yu-cheng.yu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2020-02-05 18:19 ` [RFC PATCH v9 02/27] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-02-25 20:02 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection Yu-cheng Yu
2020-02-25 20:07 ` Kees Cook
2020-02-26 17:03 ` Dave Hansen
2020-02-26 19:57 ` Pavel Machek
2020-03-05 20:38 ` Yu-cheng Yu
2020-02-26 18:05 ` Dave Hansen
2020-02-27 1:02 ` H.J. Lu
2020-02-27 1:16 ` Dave Hansen
2020-02-27 2:11 ` H.J. Lu
2020-02-27 3:57 ` Andy Lutomirski
2020-02-27 18:03 ` Dave Hansen
2020-03-06 18:37 ` Yu-cheng Yu
2020-03-06 19:02 ` Dave Hansen
2020-03-06 21:16 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 09/27] x86/mm: Introduce _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:12 ` Kees Cook
2020-02-26 21:35 ` Dave Hansen
2020-04-01 19:08 ` Yu-cheng Yu
2020-04-01 19:22 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 12/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:14 ` Kees Cook
2020-02-26 22:20 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 21/27] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND Yu-cheng Yu
2020-02-25 21:18 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 27/27] x86/cet/shstk: Add arch_prctl functions for Shadow Stack Yu-cheng Yu
2020-02-25 21:31 ` [RFC PATCH v9 00/27] Control-flow Enforcement: " Kees Cook
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