mseal sysmap: update mseal.rst

Update memory sealing documentation to include details about system
mappings.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Jeff Xu <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Reviewed-by: Liam R. Howlett <[email protected]>
Cc: Adhemerval Zanella <[email protected]>
Cc: Alexander Mikhalitsyn <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Andrei Vagin <[email protected]>
Cc: Anna-Maria Behnsen <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Benjamin Berg <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Elliot Hughes <[email protected]>
Cc: Florian Faineli <[email protected]>
Cc: Greg Ungerer <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Hyeonggon Yoo <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Jason A. Donenfeld <[email protected]>
Cc: Johannes Berg <[email protected]>
Cc: Jorge Lucangeli Obes <[email protected]>
Cc: Linus Waleij <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Matthew Wilcow (Oracle) <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Pedro Falcato <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Stephen Röttger <[email protected]>
Cc: Thomas Weißschuh <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: peaktocreek

Documentation/userspace-api/mseal.rst

@@ -130,6 +130,26 @@ Use cases
 
 - Chrome browser: protect some security sensitive data structures.
 
+- System mappings:
+  The system mappings are created by the kernel and includes vdso, vvar,
+  vvar_vclock, vectors (arm compat-mode), sigpage (arm compat-mode), uprobes.
+
+  Those system mappings are readonly only or execute only, memory sealing can
+  protect them from ever changing to writable or unmmap/remapped as different
+  attributes. This is useful to mitigate memory corruption issues where a
+  corrupted pointer is passed to a memory management system.
+
+  If supported by an architecture (CONFIG_ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS),
+  the CONFIG_MSEAL_SYSTEM_MAPPINGS seals all system mappings of this
+  architecture.
+
+  The following architectures currently support this feature: x86-64 and arm64.
+
+  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.
+
 When not to use mseal
 =====================
 Applications can apply sealing to any virtual memory region from userspace,