From 5efa8e507b937d01fca88876205b395ed8c6e2c5 Mon Sep 17 00:00:00 2001
From: Tim Schumacher <timschumi@gmx.de>
Date: Thu, 5 May 2022 18:30:24 +0200
Subject: [PATCH] Kernel: Implement an `axallowed` mount option

Similar to `W^X` and `wxallowed`, this allows for anonymous executable
mappings.
---
 Base/usr/share/man/man2/mount.md             | 1 +
 Kernel/API/POSIX/unistd.h                    | 1 +
 Kernel/Syscalls/mmap.cpp                     | 2 +-
 Userland/Applications/SystemMonitor/main.cpp | 1 +
 Userland/Utilities/mount.cpp                 | 4 ++++
 5 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/Base/usr/share/man/man2/mount.md b/Base/usr/share/man/man2/mount.md
index 9953b2dbb42..0dd9c99a41f 100644
--- a/Base/usr/share/man/man2/mount.md
+++ b/Base/usr/share/man/man2/mount.md
@@ -38,6 +38,7 @@ The following `flags` are supported:
 * `MS_RDONLY`: Mount the filesystem read-only.
 * `MS_REMOUNT`: Remount an already mounted filesystem (see below).
 * `MS_WXALLOWED`: Allow W^X protection circumvention for executables on this file system.
+* `MS_AXALLOWED`: Allow anonymous executable mappings for executables on this file system.
 
 These flags can be used as a security measure to limit the possible abuses of the newly
 mounted file system.
diff --git a/Kernel/API/POSIX/unistd.h b/Kernel/API/POSIX/unistd.h
index db26821fba4..efa35bce141 100644
--- a/Kernel/API/POSIX/unistd.h
+++ b/Kernel/API/POSIX/unistd.h
@@ -28,6 +28,7 @@ extern "C" {
 #define MS_RDONLY (1 << 4)
 #define MS_REMOUNT (1 << 5)
 #define MS_WXALLOWED (1 << 6)
+#define MS_AXALLOWED (1 << 7)
 
 enum {
     _SC_MONOTONIC_CLOCK,
diff --git a/Kernel/Syscalls/mmap.cpp b/Kernel/Syscalls/mmap.cpp
index 94d9ada8b2d..998f4b1de5f 100644
--- a/Kernel/Syscalls/mmap.cpp
+++ b/Kernel/Syscalls/mmap.cpp
@@ -75,7 +75,7 @@ ErrorOr<void> Process::validate_mmap_prot(int prot, bool map_stack, bool map_ano
     bool make_writable = prot & PROT_WRITE;
     bool make_executable = prot & PROT_EXEC;
 
-    if (map_anonymous && make_executable)
+    if (map_anonymous && make_executable && !(executable()->mount_flags() & MS_AXALLOWED))
         return EINVAL;
 
     if (map_stack && make_executable)
diff --git a/Userland/Applications/SystemMonitor/main.cpp b/Userland/Applications/SystemMonitor/main.cpp
index a97f4c3a125..98065b3599a 100644
--- a/Userland/Applications/SystemMonitor/main.cpp
+++ b/Userland/Applications/SystemMonitor/main.cpp
@@ -287,6 +287,7 @@ public:
                 check(MS_BIND, "bind");
                 check(MS_RDONLY, "ro");
                 check(MS_WXALLOWED, "wxallowed");
+                check(MS_AXALLOWED, "axallowed");
                 if (builder.string_view().is_empty())
                     return String("defaults");
                 return builder.to_string();
diff --git a/Userland/Utilities/mount.cpp b/Userland/Utilities/mount.cpp
index 8479d7b5fb0..ac19c70e922 100644
--- a/Userland/Utilities/mount.cpp
+++ b/Userland/Utilities/mount.cpp
@@ -38,6 +38,8 @@ static int parse_options(StringView options)
             flags |= MS_REMOUNT;
         else if (part == "wxallowed")
             flags |= MS_WXALLOWED;
+        else if (part == "axallowed")
+            flags |= MS_AXALLOWED;
         else
             warnln("Ignoring invalid option: {}", part);
     }
@@ -180,6 +182,8 @@ static ErrorOr<void> print_mounts()
             out(",bind");
         if (mount_flags & MS_WXALLOWED)
             out(",wxallowed");
+        if (mount_flags & MS_AXALLOWED)
+            out(",axallowed");
 
         outln(")");
     });