linux-hardening - [PATCH v9 1/7] mseal sysmap: kernel config and header change

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Message-ID: <20250305021711.3867874-2-jeffxu@google.com>
Date: Wed,  5 Mar 2025 02:17:05 +0000
From: jeffxu@...omium.org
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	Jeff Xu <jeffxu@...omium.org>,
	Kees Cook <kees@...nel.org>
Subject: [PATCH v9 1/7] mseal sysmap: kernel config and header change

From: Jeff Xu <jeffxu@...omium.org>

Provide infrastructure to mseal system mappings. Establish
two kernel configs (CONFIG_MSEAL_SYSTEM_MAPPINGS,
ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS) and VM_SEALED_SYSMAP
macro for future patches.

Signed-off-by: Jeff Xu <jeffxu@...omium.org>
Reviewed-by: Kees Cook <kees@...nel.org>
---
 include/linux/mm.h | 10 ++++++++++
 init/Kconfig       | 22 ++++++++++++++++++++++
 security/Kconfig   | 21 +++++++++++++++++++++
 3 files changed, 53 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7b1068ddcbb7..8b800941678d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4155,4 +4155,14 @@ int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *st
 int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status);
 int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
 
+
+/*
+ * mseal of userspace process's system mappings.
+ */
+#ifdef CONFIG_MSEAL_SYSTEM_MAPPINGS
+#define VM_SEALED_SYSMAP	VM_SEALED
+#else
+#define VM_SEALED_SYSMAP	VM_NONE
+#endif
+
 #endif /* _LINUX_MM_H */
diff --git a/init/Kconfig b/init/Kconfig
index d0d021b3fa3b..7f67d8942a09 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1882,6 +1882,28 @@ config ARCH_HAS_MEMBARRIER_CALLBACKS
 config ARCH_HAS_MEMBARRIER_SYNC_CORE
 	bool
 
+config ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
+	bool
+	help
+	  Control MSEAL_SYSTEM_MAPPINGS access based on architecture.
+
+	  A 64-bit kernel is required for the memory sealing feature.
+	  No specific hardware features from the CPU are needed.
+
+	  To enable this feature, the architecture needs to update their
+	  special mappings calls to include the sealing flag and confirm
+	  that it doesn't unmap/remap system mappings during the life
+	  time of the process. The existence of this flag for an architecture
+	  implies that it does not require the remapping of the system
+	  mappings during process lifetime, so sealing these mappings is safe
+	  from a kernel perspective.
+
+	  After the architecture enables this, a distribution can set
+	  CONFIG_MSEAL_SYSTEM_MAPPING to manage access to the feature.
+
+	  For complete descriptions of memory sealing, please see
+	  Documentation/userspace-api/mseal.rst
+
 config HAVE_PERF_EVENTS
 	bool
 	help
diff --git a/security/Kconfig b/security/Kconfig
index f10dbf15c294..a914a02df27e 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -51,6 +51,27 @@ config PROC_MEM_NO_FORCE
 
 endchoice
 
+config MSEAL_SYSTEM_MAPPINGS
+	bool "mseal system mappings"
+	depends on 64BIT
+	depends on ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
+	depends on !CHECKPOINT_RESTORE
+	help
+	  Apply mseal on system mappings.
+	  The system mappings includes vdso, vvar, vvar_vclock,
+	  vectors (arm compat-mode), sigpage (arm compat-mode), uprobes.
+
+	  A 64-bit kernel is required for the memory sealing feature.
+	  No specific hardware features from the CPU are needed.
+
+	  WARNING: This feature breaks programs which rely on relocating
+	  or unmapping system mappings. Known broken software at the time
+	  of writing includes CHECKPOINT_RESTORE, UML, gVisor, rr. Therefore
+	  this config can't be enabled universally.
+
+	  For complete descriptions of memory sealing, please see
+	  Documentation/userspace-api/mseal.rst
+
 config SECURITY
 	bool "Enable different security models"
 	depends on SYSFS
-- 
2.48.1.711.g2feabab25a-goog