[PATCH v3 2/2] ipe: Update documentation for script enforcement

[Yanzhu Huang <yanzhuhuang@linux.microsoft.com>]

This patch adds explanation of script enforcement mechanism in admin
guide documentation. Describes how IPE supports integrity enforcement
for indirectly executed scripts through the AT_EXECVE_CHECK flag, and
how this differs from kernel enforcement for compiled executables.

Signed-off-by: Yanzhu Huang <yanzhuhuang@linux.microsoft.com>
---
 Documentation/admin-guide/LSM/ipe.rst | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/LSM/ipe.rst b/Documentation/admin-guide/LSM/ipe.rst
index dc7088451f9d..a756d8158531 100644
--- a/Documentation/admin-guide/LSM/ipe.rst
+++ b/Documentation/admin-guide/LSM/ipe.rst
@@ -95,7 +95,20 @@ languages when these scripts are invoked by passing these program files
 to the interpreter. This is because the way interpreters execute these
 files; the scripts themselves are not evaluated as executable code
 through one of IPE's hooks, but they are merely text files that are read
-(as opposed to compiled executables) [#interpreters]_.
+(as opposed to compiled executables). However, with the introduction of the
+``AT_EXECVE_CHECK`` flag (:doc:`AT_EXECVE_CHECK </userspace-api/check_exec>`),
+interpreters can use it to signal the kernel that a script file will be executed,
+and request the kernel to perform LSM security checks on it.
+
+IPE's EXECUTE operation enforcement differs between compiled executables and
+interpreted scripts: For compiled executables, enforcement is triggered
+automatically by the kernel during ``execve()``, ``execveat()``, ``mmap()``
+and ``mprotect()`` syscalls when loading executable content. For interpreted
+scripts, enforcement requires explicit interpreter integration using
+``execveat()`` with ``AT_EXECVE_CHECK`` flag. Unlike exec syscalls that IPE
+intercepts during the execution process, this mechanism needs the interpreter
+to take the initiative, and existing interpreters won't be automatically
+supported unless the signal call is added.
 
 Threat Model
 ------------
@@ -806,8 +819,6 @@ A:
 
 .. [#digest_cache_lsm] https://lore.kernel.org/lkml/20240415142436.2545003-1-roberto.sassu@huaweicloud.com/
 
-.. [#interpreters] There is `some interest in solving this issue <https://lore.kernel.org/lkml/20220321161557.495388-1-mic@digikod.net/>`_.
-
 .. [#devdoc] Please see :doc:`the design docs </security/ipe>` for more on
              this topic.
 
-- 
2.43.0