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From: Rick Edgecombe <rick.p.edgecombe@intel.com>
To: 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>,
	Weijiang Yang <weijiang.yang@intel.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	John Allen <john.allen@amd.com>,
	kcc@google.com, eranian@google.com, rppt@kernel.org,
	jamorris@linux.microsoft.com, dethoma@microsoft.com,
	akpm@linux-foundation.org, Andrew.Cooper3@citrix.com,
	christina.schimpe@intel.com, david@redhat.com,
	debug@rivosinc.com, szabolcs.nagy@arm.com,
	torvalds@linux-foundation.org, broonie@kernel.org
Cc: rick.p.edgecombe@intel.com, Yu-cheng Yu <yu-cheng.yu@intel.com>,
	Pengfei Xu <pengfei.xu@intel.com>
Subject: [PATCH v9 23/42] Documentation/x86: Add CET shadow stack description
Date: Mon, 12 Jun 2023 17:10:49 -0700	[thread overview]
Message-ID: <20230613001108.3040476-24-rick.p.edgecombe@intel.com> (raw)
In-Reply-To: <20230613001108.3040476-1-rick.p.edgecombe@intel.com>

Introduce a new document on Control-flow Enforcement Technology (CET).

Co-developed-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
---
 Documentation/arch/x86/index.rst |   1 +
 Documentation/arch/x86/shstk.rst | 169 +++++++++++++++++++++++++++++++
 2 files changed, 170 insertions(+)
 create mode 100644 Documentation/arch/x86/shstk.rst

diff --git a/Documentation/arch/x86/index.rst b/Documentation/arch/x86/index.rst
index c73d133fd37c..8ac64d7de4dc 100644
--- a/Documentation/arch/x86/index.rst
+++ b/Documentation/arch/x86/index.rst
@@ -22,6 +22,7 @@ x86-specific Documentation
    mtrr
    pat
    intel-hfi
+   shstk
    iommu
    intel_txt
    amd-memory-encryption
diff --git a/Documentation/arch/x86/shstk.rst b/Documentation/arch/x86/shstk.rst
new file mode 100644
index 000000000000..f09afa504ec0
--- /dev/null
+++ b/Documentation/arch/x86/shstk.rst
@@ -0,0 +1,169 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======================================================
+Control-flow Enforcement Technology (CET) Shadow Stack
+======================================================
+
+CET Background
+==============
+
+Control-flow Enforcement Technology (CET) covers several related x86 processor
+features that provide protection against control flow hijacking attacks. CET
+can protect both applications and the kernel.
+
+CET introduces shadow stack and indirect branch tracking (IBT). A shadow stack
+is a secondary stack allocated from memory which cannot be directly modified by
+applications. When executing a CALL instruction, the processor pushes the
+return address to both the normal stack and the shadow stack. Upon
+function return, the processor pops the shadow stack copy and compares it
+to the normal stack copy. If the two differ, the processor raises a
+control-protection fault. IBT verifies indirect CALL/JMP targets are intended
+as marked by the compiler with 'ENDBR' opcodes. Not all CPU's have both Shadow
+Stack and Indirect Branch Tracking. Today in the 64-bit kernel, only userspace
+shadow stack and kernel IBT are supported.
+
+Requirements to use Shadow Stack
+================================
+
+To use userspace shadow stack you need HW that supports it, a kernel
+configured with it and userspace libraries compiled with it.
+
+The kernel Kconfig option is X86_USER_SHADOW_STACK.  When compiled in, shadow
+stacks can be disabled at runtime with the kernel parameter: nousershstk.
+
+To build a user shadow stack enabled kernel, Binutils v2.29 or LLVM v6 or later
+are required.
+
+At run time, /proc/cpuinfo shows CET features if the processor supports
+CET. "user_shstk" means that userspace shadow stack is supported on the current
+kernel and HW.
+
+Application Enabling
+====================
+
+An application's CET capability is marked in its ELF note and can be verified
+from readelf/llvm-readelf output::
+
+    readelf -n <application> | grep -a SHSTK
+        properties: x86 feature: SHSTK
+
+The kernel does not process these applications markers directly. Applications
+or loaders must enable CET features using the interface described in section 4.
+Typically this would be done in dynamic loader or static runtime objects, as is
+the case in GLIBC.
+
+Enabling arch_prctl()'s
+=======================
+
+Elf features should be enabled by the loader using the below arch_prctl's. They
+are only supported in 64 bit user applications. These operate on the features
+on a per-thread basis. The enablement status is inherited on clone, so if the
+feature is enabled on the first thread, it will propagate to all the thread's
+in an app.
+
+arch_prctl(ARCH_SHSTK_ENABLE, unsigned long feature)
+    Enable a single feature specified in 'feature'. Can only operate on
+    one feature at a time.
+
+arch_prctl(ARCH_SHSTK_DISABLE, unsigned long feature)
+    Disable a single feature specified in 'feature'. Can only operate on
+    one feature at a time.
+
+arch_prctl(ARCH_SHSTK_LOCK, unsigned long features)
+    Lock in features at their current enabled or disabled status. 'features'
+    is a mask of all features to lock. All bits set are processed, unset bits
+    are ignored. The mask is ORed with the existing value. So any feature bits
+    set here cannot be enabled or disabled afterwards.
+
+The return values are as follows. On success, return 0. On error, errno can
+be::
+
+        -EPERM if any of the passed feature are locked.
+        -ENOTSUPP if the feature is not supported by the hardware or
+         kernel.
+        -EINVAL arguments (non existing feature, etc)
+
+The feature's bits supported are::
+
+    ARCH_SHSTK_SHSTK - Shadow stack
+    ARCH_SHSTK_WRSS  - WRSS
+
+Currently shadow stack and WRSS are supported via this interface. WRSS
+can only be enabled with shadow stack, and is automatically disabled
+if shadow stack is disabled.
+
+Proc Status
+===========
+To check if an application is actually running with shadow stack, the
+user can read the /proc/$PID/status. It will report "wrss" or "shstk"
+depending on what is enabled. The lines look like this::
+
+    x86_Thread_features: shstk wrss
+    x86_Thread_features_locked: shstk wrss
+
+Implementation of the Shadow Stack
+==================================
+
+Shadow Stack Size
+-----------------
+
+A task's shadow stack is allocated from memory to a fixed size of
+MIN(RLIMIT_STACK, 4 GB). In other words, the shadow stack is allocated to
+the maximum size of the normal stack, but capped to 4 GB. In the case
+of the clone3 syscall, there is a stack size passed in and shadow stack
+uses this instead of the rlimit.
+
+Signal
+------
+
+The main program and its signal handlers use the same shadow stack. Because
+the shadow stack stores only return addresses, a large shadow stack covers
+the condition that both the program stack and the signal alternate stack run
+out.
+
+When a signal happens, the old pre-signal state is pushed on the stack. When
+shadow stack is enabled, the shadow stack specific state is pushed onto the
+shadow stack. Today this is only the old SSP (shadow stack pointer), pushed
+in a special format with bit 63 set. On sigreturn this old SSP token is
+verified and restored by the kernel. The kernel will also push the normal
+restorer address to the shadow stack to help userspace avoid a shadow stack
+violation on the sigreturn path that goes through the restorer.
+
+So the shadow stack signal frame format is as follows::
+
+    |1...old SSP| - Pointer to old pre-signal ssp in sigframe token format
+                    (bit 63 set to 1)
+    |        ...| - Other state may be added in the future
+
+
+32 bit ABI signals are not supported in shadow stack processes. Linux prevents
+32 bit execution while shadow stack is enabled by the allocating shadow stacks
+outside of the 32 bit address space. When execution enters 32 bit mode, either
+via far call or returning to userspace, a #GP is generated by the hardware
+which, will be delivered to the process as a segfault. When transitioning to
+userspace the register's state will be as if the userspace ip being returned to
+caused the segfault.
+
+Fork
+----
+
+The shadow stack's vma has VM_SHADOW_STACK flag set; its PTEs are required
+to be read-only and dirty. When a shadow stack PTE is not RO and dirty, a
+shadow access triggers a page fault with the shadow stack access bit set
+in the page fault error code.
+
+When a task forks a child, its shadow stack PTEs are copied and both the
+parent's and the child's shadow stack PTEs are cleared of the dirty bit.
+Upon the next shadow stack access, the resulting shadow stack page fault
+is handled by page copy/re-use.
+
+When a pthread child is created, the kernel allocates a new shadow stack
+for the new thread. New shadow stack creation behaves like mmap() with respect
+to ASLR behavior. Similarly, on thread exit the thread's shadow stack is
+disabled.
+
+Exec
+----
+
+On exec, shadow stack features are disabled by the kernel. At which point,
+userspace can choose to re-enable, or lock them.
-- 
2.34.1


  parent reply	other threads:[~2023-06-13  0:16 UTC|newest]

Thread overview: 151+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-13  0:10 [PATCH v9 00/42] Shadow stacks for userspace Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 01/42] mm: Rename arch pte_mkwrite()'s to pte_mkwrite_novma() Rick Edgecombe
2023-06-13  7:19   ` Geert Uytterhoeven
2023-06-13 16:14     ` Edgecombe, Rick P
2023-06-13  7:43   ` Mike Rapoport
2023-06-13 16:14     ` Edgecombe, Rick P
2023-06-13 12:26   ` David Hildenbrand
2023-06-13 16:14     ` Edgecombe, Rick P
2023-06-19  4:27   ` Helge Deller
2023-07-14 22:57   ` Mark Brown
2023-07-17 15:55     ` Edgecombe, Rick P
2023-07-17 16:51       ` Mark Brown
2023-06-13  0:10 ` [PATCH v9 02/42] mm: Move pte/pmd_mkwrite() callers with no VMA to _novma() Rick Edgecombe
2023-06-13  7:44   ` Mike Rapoport
2023-06-13 16:19     ` Edgecombe, Rick P
2023-06-13 17:00       ` David Hildenbrand
2023-06-14 17:00         ` Edgecombe, Rick P
2023-06-13 12:27   ` David Hildenbrand
2023-06-13 16:20     ` Edgecombe, Rick P
2023-06-13  0:10 ` [PATCH v9 03/42] mm: Make pte_mkwrite() take a VMA Rick Edgecombe
2023-06-13  7:42   ` Mike Rapoport
2023-06-13 16:20     ` Edgecombe, Rick P
2023-06-13 12:28   ` David Hildenbrand
2023-06-13 16:21     ` Edgecombe, Rick P
2023-06-13  0:10 ` [PATCH v9 04/42] mm: Re-introduce vm_flags to do_mmap() Rick Edgecombe
2023-06-14  8:49   ` David Hildenbrand
2023-06-14 23:30   ` Mark Brown
2023-06-13  0:10 ` [PATCH v9 05/42] mm: Move VM_UFFD_MINOR_BIT from 37 to 38 Rick Edgecombe
2023-06-14  8:50   ` David Hildenbrand
2023-06-13  0:10 ` [PATCH v9 06/42] x86/shstk: Add Kconfig option for shadow stack Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 07/42] x86/traps: Move control protection handler to separate file Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 08/42] x86/cpufeatures: Add CPU feature flags for shadow stacks Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 09/42] x86/mm: Move pmd_write(), pud_write() up in the file Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 10/42] x86/mm: Introduce _PAGE_SAVED_DIRTY Rick Edgecombe
2023-06-13 16:01   ` Edgecombe, Rick P
2023-06-13 17:58   ` Linus Torvalds
2023-06-13 19:37     ` Edgecombe, Rick P
2023-06-13  0:10 ` [PATCH v9 11/42] x86/mm: Update ptep/pmdp_set_wrprotect() for _PAGE_SAVED_DIRTY Rick Edgecombe
2023-06-13 18:01   ` Linus Torvalds
2023-06-13  0:10 ` [PATCH v9 12/42] x86/mm: Start actually marking _PAGE_SAVED_DIRTY Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 13/42] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 14/42] mm: Introduce VM_SHADOW_STACK for shadow stack memory Rick Edgecombe
2023-06-14  8:50   ` David Hildenbrand
2023-06-14 23:31   ` Mark Brown
2023-06-13  0:10 ` [PATCH v9 15/42] x86/mm: Check shadow stack page fault errors Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 16/42] mm: Add guard pages around a shadow stack Rick Edgecombe
2023-06-14 23:34   ` Mark Brown
2023-06-22 18:21   ` Matthew Wilcox
2023-06-22 18:27     ` Edgecombe, Rick P
2023-06-23  7:40       ` Mike Rapoport
2023-06-23 12:17         ` Mark Brown
2023-06-25 16:44           ` Edgecombe, Rick P
2023-06-26 12:45             ` Mark Brown
2023-07-06 23:32               ` [PATCH] x86/shstk: Move arch detail comment out of core mm Rick Edgecombe
2023-07-07 15:08                 ` Mark Brown
2023-08-01 16:52                 ` Mike Rapoport
2023-06-13  0:10 ` [PATCH v9 17/42] mm: Warn on shadow stack memory in wrong vma Rick Edgecombe
2023-06-14 23:35   ` Mark Brown
2023-06-13  0:10 ` [PATCH v9 18/42] x86/mm: Warn if create Write=0,Dirty=1 with raw prot Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 19/42] mm/mmap: Add shadow stack pages to memory accounting Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 20/42] x86/mm: Introduce MAP_ABOVE4G Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 21/42] x86/mm: Teach pte_mkwrite() about stack memory Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 22/42] mm: Don't allow write GUPs to shadow " Rick Edgecombe
2023-06-13  0:10 ` Rick Edgecombe [this message]
2023-06-13 11:55   ` [PATCH v9 23/42] Documentation/x86: Add CET shadow stack description Mark Brown
2023-06-13 12:37     ` Florian Weimer
2023-06-13 15:15       ` Mark Brown
2023-06-13 17:11         ` Edgecombe, Rick P
2023-06-13 17:57           ` Mark Brown
2023-06-13 19:57             ` Edgecombe, Rick P
2023-06-14 10:43               ` szabolcs.nagy
2023-06-14 16:57                 ` Edgecombe, Rick P
2023-06-19  8:47                   ` szabolcs.nagy
2023-06-19 16:44                     ` Edgecombe, Rick P
2023-06-20  9:17                       ` szabolcs.nagy
2023-06-20 19:34                         ` Edgecombe, Rick P
2023-06-21 11:36                           ` szabolcs.nagy
2023-06-21 18:54                             ` Edgecombe, Rick P
2023-06-21 22:22                               ` Edgecombe, Rick P
2023-06-21 23:05                                 ` H.J. Lu
2023-06-21 23:15                                   ` Edgecombe, Rick P
2023-06-22  1:07                                     ` Edgecombe, Rick P
2023-06-22  3:23                                       ` H.J. Lu
2023-06-22  8:27                                 ` szabolcs.nagy
2023-06-22 16:47                                   ` Edgecombe, Rick P
2023-06-23 16:25                                     ` szabolcs.nagy
2023-06-25 18:48                                       ` Edgecombe, Rick P
2023-06-21 23:02                               ` H.J. Lu
2023-06-22  7:40                                 ` szabolcs.nagy
2023-06-22 16:46                                   ` Edgecombe, Rick P
2023-06-26 14:08                                     ` szabolcs.nagy
2023-06-28  1:23                                       ` Edgecombe, Rick P
2023-06-22  9:18                               ` szabolcs.nagy
2023-06-22 15:26                                 ` Andy Lutomirski
2023-06-22 16:42                                   ` szabolcs.nagy
2023-06-22 23:18                                     ` Edgecombe, Rick P
2023-06-29 16:07                                       ` szabolcs.nagy
2023-07-02 18:03                                         ` Edgecombe, Rick P
2023-07-03 13:32                                           ` Mark Brown
2023-07-03 18:19                                           ` szabolcs.nagy
2023-07-03 18:38                                             ` Mark Brown
2023-07-03 18:49                                             ` Florian Weimer
2023-07-04 11:33                                               ` Szabolcs Nagy
2023-07-05 18:45                                             ` Edgecombe, Rick P
2023-07-05 19:10                                               ` Mark Brown
2023-07-05 19:17                                                 ` Edgecombe, Rick P
2023-07-05 19:29                                                   ` Mark Brown
2023-07-06 13:14                                                     ` szabolcs.nagy
2023-07-06 14:24                                                       ` Mark Brown
2023-07-06 16:59                                                         ` Edgecombe, Rick P
2023-07-06 19:03                                                           ` Mark Brown
2023-07-06 13:07                                               ` szabolcs.nagy
2023-07-06 18:25                                                 ` Edgecombe, Rick P
2023-07-07 15:25                                                   ` szabolcs.nagy
2023-07-07 17:37                                                     ` Edgecombe, Rick P
2023-07-10 16:54                                                       ` szabolcs.nagy
2023-07-10 22:56                                                         ` Edgecombe, Rick P
2023-07-11  8:08                                                           ` szabolcs.nagy
2023-07-12  9:39                                                             ` Szabolcs Nagy
2023-06-25 23:52                                     ` Andy Lutomirski
2023-06-14 13:12               ` Mark Brown
2023-07-18 19:32   ` Szabolcs Nagy
2023-06-13  0:10 ` [PATCH v9 24/42] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 25/42] x86/fpu: Add helper for modifying xstate Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 26/42] x86: Introduce userspace API for shadow stack Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 27/42] x86/shstk: Add user control-protection fault handler Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 28/42] x86/shstk: Add user-mode shadow stack support Rick Edgecombe
2023-06-27 17:20   ` Mark Brown
2023-06-27 23:46     ` Dave Hansen
2023-06-28  0:37       ` Edgecombe, Rick P
2023-07-06 23:38         ` [PATCH] x86/shstk: Don't retry vm_munmap() on -EINTR Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 29/42] x86/shstk: Handle thread shadow stack Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 30/42] x86/shstk: Introduce routines modifying shstk Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 31/42] x86/shstk: Handle signals for shadow stack Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 32/42] x86/shstk: Check that SSP is aligned on sigreturn Rick Edgecombe
2023-06-13  0:10 ` [PATCH v9 33/42] x86/shstk: Check that signal frame is shadow stack mem Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 34/42] x86/shstk: Introduce map_shadow_stack syscall Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 35/42] x86/shstk: Support WRSS for userspace Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 36/42] x86: Expose thread features in /proc/$PID/status Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 37/42] x86/shstk: Wire in shadow stack interface Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 38/42] x86/cpufeatures: Enable CET CR4 bit for shadow stack Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 39/42] selftests/x86: Add shadow stack test Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 40/42] x86: Add PTRACE interface for shadow stack Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 41/42] x86/shstk: Add ARCH_SHSTK_UNLOCK Rick Edgecombe
2023-06-13  0:11 ` [PATCH v9 42/42] x86/shstk: Add ARCH_SHSTK_STATUS Rick Edgecombe
2023-06-13  1:34 ` [PATCH v9 00/42] Shadow stacks for userspace Linus Torvalds
2023-06-13  3:12   ` Edgecombe, Rick P
2023-06-13 17:44     ` Linus Torvalds
2023-06-13 18:27       ` Linus Torvalds
2023-06-13 19:38         ` Edgecombe, Rick P
2023-06-14 23:45 ` Mark Brown

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