From da13c9a2648de7c7d799952389e228e739dc486d Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Sat, 3 Nov 2018 11:36:45 +0100
Subject: [PATCH] Map pages in read-only ELF sections as non-writable.

This is so cool! :^) Now you'll crash if you try to write into your
.text or .rodata segments.
---
 Kernel/MemoryManager.cpp |  6 +++---
 Kernel/MemoryManager.h   |  4 +++-
 Kernel/Process.cpp       |  6 ++++--
 Userland/sh.cpp          | 16 ++++++++++++++++
 4 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/Kernel/MemoryManager.cpp b/Kernel/MemoryManager.cpp
index f86cbd315b..7dd4cd6cb5 100644
--- a/Kernel/MemoryManager.cpp
+++ b/Kernel/MemoryManager.cpp
@@ -304,8 +304,8 @@ void MemoryManager::map_region_at_address(PageDirectory* page_directory, Region&
         auto page_laddr = laddr.offset(i * PAGE_SIZE);
         auto pte = ensurePTE(page_directory, page_laddr);
         pte.setPhysicalPageBase(zone.m_pages[i].get());
-        pte.setPresent(true);
-        pte.setWritable(true);
+        pte.setPresent(true); // FIXME: Maybe we could use the is_readable flag here?
+        pte.setWritable(region.is_writable);
         pte.setUserAllowed(user_allowed);
         flushTLB(page_laddr);
 #ifdef MM_DEBUG
@@ -430,7 +430,7 @@ RetainPtr<Region> Region::clone()
 
     // FIXME: Implement COW regions.
     auto clone_zone = MM.createZone(zone->size());
-    auto clone_region = adopt(*new Region(linearAddress, size, move(clone_zone), String(name)));
+    auto clone_region = adopt(*new Region(linearAddress, size, move(clone_zone), String(name), is_readable, is_writable));
 
     // FIXME: It would be cool to make the src_alias a read-only mapping.
     byte* src_alias = MM.create_kernel_alias_for_region(*this);
diff --git a/Kernel/MemoryManager.h b/Kernel/MemoryManager.h
index 3c3df0d58d..0ebe056666 100644
--- a/Kernel/MemoryManager.h
+++ b/Kernel/MemoryManager.h
@@ -38,7 +38,7 @@ private:
 };
 
 struct Region : public Retainable<Region> {
-    Region(LinearAddress, size_t, RetainPtr<Zone>&&, String&&);
+    Region(LinearAddress, size_t, RetainPtr<Zone>&&, String&&, bool r, bool w);
     ~Region();
 
     RetainPtr<Region> clone();
@@ -46,6 +46,8 @@ struct Region : public Retainable<Region> {
     size_t size { 0 };
     RetainPtr<Zone> zone;
     String name;
+    bool is_readable { true };
+    bool is_writable { true };
 };
 
 #define MM MemoryManager::the()
diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index 1f622fc2c1..8f9ac2bcbc 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -147,7 +147,7 @@ Region* Process::allocate_region(LinearAddress laddr, size_t size, String&& name
     auto zone = MM.createZone(size);
     ASSERT(zone);
 
-    m_regions.append(adopt(*new Region(laddr, size, move(zone), move(name))));
+    m_regions.append(adopt(*new Region(laddr, size, move(zone), move(name), is_readable, is_writable)));
 
     MM.mapRegion(*this, *m_regions.last());
     return m_regions.last().ptr();
@@ -1260,11 +1260,13 @@ Process* Process::kernelProcess()
     return s_kernelProcess;
 }
 
-Region::Region(LinearAddress a, size_t s, RetainPtr<Zone>&& z, String&& n)
+Region::Region(LinearAddress a, size_t s, RetainPtr<Zone>&& z, String&& n, bool r, bool w)
     : linearAddress(a)
     , size(s)
     , zone(move(z))
     , name(move(n))
+    , is_readable(r)
+    , is_writable(w)
 {
 }
 
diff --git a/Userland/sh.cpp b/Userland/sh.cpp
index 8df8ae9c58..1ec61c2ed4 100644
--- a/Userland/sh.cpp
+++ b/Userland/sh.cpp
@@ -65,6 +65,18 @@ static int sh_fef(int, const char**)
     return 0;
 }
 
+static int sh_wt(int, const char**)
+{
+    const char* rodata_ptr = "foo";
+    printf("Writing to rodata=%p...\n", rodata_ptr);
+    *(char*)rodata_ptr = 0;
+
+    char* text_ptr = (char*)sh_fef;
+    printf("Writing to text=%p...\n", text_ptr);
+    *text_ptr = 0;
+    return 0;
+}
+
 static int sh_exit(int, const char**)
 {
     printf("Good-bye!\n");
@@ -135,6 +147,10 @@ static bool handle_builtin(int argc, const char** argv, int& retval)
         retval = sh_fef(argc, argv);
         return true;
     }
+    if (!strcmp(argv[0], "wt")) {
+        retval = sh_wt(argc, argv);
+        return true;
+    }
     if (!strcmp(argv[0], "fork")) {
         retval = sh_fork(argc, argv);
         return true;