Kernel/Memory: Add option to annotate region mapping as immutable

We add this basic functionality to the Kernel so Userspace can request a
particular virtual memory mapping to be immutable. This will be useful
later on in the DynamicLoader code.

The annotation of a particular Kernel Region as immutable implies that
the following restrictions apply, so these features are prohibited:
- Changing the region's protection bits
- Unmapping the region
- Annotating the region with other virtual memory flags
- Applying further memory advises on the region
- Changing the region name
- Re-mapping the region

4 files changed, 35 insertions, 4 deletions

diff --git a/Kernel/API/VirtualMemoryAnnotations.h b/Kernel/API/VirtualMemoryAnnotations.h
index ec140bd927..bed3ffe113 100644
--- a/Kernel/API/VirtualMemoryAnnotations.h
+++ b/Kernel/API/VirtualMemoryAnnotations.h
@@ -14,6 +14,7 @@ namespace Kernel {
 enum class VirtualMemoryRangeFlags : u32 {
     None = 0,
     SyscallCode = 1 << 0,
+    Immutable = 1 << 1,
 };
 
 AK_ENUM_BITWISE_OPERATORS(VirtualMemoryRangeFlags);
diff --git a/Kernel/Memory/AddressSpace.cpp b/Kernel/Memory/AddressSpace.cpp
index e37d3f22c3..1fa839afdb 100644
--- a/Kernel/Memory/AddressSpace.cpp
+++ b/Kernel/Memory/AddressSpace.cpp
@@ -59,6 +59,8 @@ ErrorOr<void> AddressSpace::unmap_mmap_range(VirtualAddress addr, size_t size)
     if (auto* whole_region = find_region_from_range(range_to_unmap)) {
         if (!whole_region->is_mmap())
             return EPERM;
+        if (whole_region->is_immutable())
+            return EPERM;
 
         PerformanceManager::add_unmap_perf_event(Process::current(), whole_region->range());
 
@@ -69,6 +71,8 @@ ErrorOr<void> AddressSpace::unmap_mmap_range(VirtualAddress addr, size_t size)
     if (auto* old_region = find_region_containing(range_to_unmap)) {
         if (!old_region->is_mmap())
             return EPERM;
+        if (old_region->is_immutable())
+            return EPERM;
 
         // Remove the old region from our regions tree, since were going to add another region
         // with the exact same start address.
@@ -99,6 +103,8 @@ ErrorOr<void> AddressSpace::unmap_mmap_range(VirtualAddress addr, size_t size)
     for (auto* region : regions) {
         if (!region->is_mmap())
             return EPERM;
+        if (region->is_immutable())
+            return EPERM;
     }
 
     Vector<Region*, 2> new_regions;
diff --git a/Kernel/Memory/Region.h b/Kernel/Memory/Region.h
index aabceef63d..bc435e3841 100644
--- a/Kernel/Memory/Region.h
+++ b/Kernel/Memory/Region.h
@@ -88,6 +88,9 @@ public:
     [[nodiscard]] bool is_stack() const { return m_stack; }
     void set_stack(bool stack) { m_stack = stack; }
 
+    [[nodiscard]] bool is_immutable() const { return m_immutable; }
+    void set_immutable() { m_immutable = true; }
+
     [[nodiscard]] bool is_mmap() const { return m_mmap; }
 
     void set_mmap(bool mmap, bool description_was_readable, bool description_was_writable)
@@ -235,6 +238,7 @@ private:
     bool m_cacheable : 1 { false };
     bool m_stack : 1 { false };
     bool m_mmap : 1 { false };
+    bool m_immutable : 1 { false };
     bool m_syscall_region : 1 { false };
     bool m_write_combine : 1 { false };
     bool m_mmapped_from_readable : 1 { false };
diff --git a/Kernel/Syscalls/mmap.cpp b/Kernel/Syscalls/mmap.cpp
index 87a7b32bce..0b2d7f4596 100644
--- a/Kernel/Syscalls/mmap.cpp
+++ b/Kernel/Syscalls/mmap.cpp
@@ -284,6 +284,8 @@ ErrorOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int p
         if (auto* whole_region = space->find_region_from_range(range_to_mprotect)) {
             if (!whole_region->is_mmap())
                 return EPERM;
+            if (whole_region->is_immutable())
+                return EPERM;
             TRY(validate_mmap_prot(prot, whole_region->is_stack(), whole_region->vmobject().is_anonymous(), whole_region));
             if (whole_region->access() == Memory::prot_to_region_access_flags(prot))
                 return 0;
@@ -301,6 +303,8 @@ ErrorOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int p
         if (auto* old_region = space->find_region_containing(range_to_mprotect)) {
             if (!old_region->is_mmap())
                 return EPERM;
+            if (old_region->is_immutable())
+                return EPERM;
             TRY(validate_mmap_prot(prot, old_region->is_stack(), old_region->vmobject().is_anonymous(), old_region));
             if (old_region->access() == Memory::prot_to_region_access_flags(prot))
                 return 0;
@@ -336,6 +340,8 @@ ErrorOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int p
             for (auto const* region : regions) {
                 if (!region->is_mmap())
                     return EPERM;
+                if (region->is_immutable())
+                    return EPERM;
                 TRY(validate_mmap_prot(prot, region->is_stack(), region->vmobject().is_anonymous(), region));
                 if (region->vmobject().is_inode())
                     TRY(validate_inode_mmap_prot(prot, region->mmapped_from_readable(), region->mmapped_from_writable(), region->is_shared()));
@@ -415,6 +421,8 @@ ErrorOr<FlatPtr> Process::sys$madvise(Userspace<void*> address, size_t size, int
             return EINVAL;
         if (!region->is_mmap())
             return EPERM;
+        if (region->is_immutable())
+            return EPERM;
         if (advice == MADV_SET_VOLATILE || advice == MADV_SET_NONVOLATILE) {
             if (!region->vmobject().is_anonymous())
                 return EINVAL;
@@ -448,6 +456,9 @@ ErrorOr<FlatPtr> Process::sys$set_mmap_name(Userspace<Syscall::SC_set_mmap_name_
         if (!region->is_mmap())
             return EPERM;
 
+        if (region->is_immutable())
+            return EPERM;
+
         region->set_name(move(name));
         PerformanceManager::add_mmap_perf_event(*this, *region);
 
@@ -481,6 +492,9 @@ ErrorOr<FlatPtr> Process::sys$mremap(Userspace<Syscall::SC_mremap_params const*>
         if (!old_region->is_mmap())
             return EPERM;
 
+        if (old_region->is_immutable())
+            return EPERM;
+
         if (old_region->vmobject().is_shared_inode() && params.flags & MAP_PRIVATE && !(params.flags & (MAP_ANONYMOUS | MAP_NORESERVE))) {
             auto range = old_region->range();
             auto old_prot = region_access_flags_to_prot(old_region->access());
@@ -567,7 +581,10 @@ ErrorOr<FlatPtr> Process::sys$annotate_mapping(Userspace<void*> address, int fla
     VERIFY_NO_PROCESS_BIG_LOCK(this);
 
     return address_space().with([&](auto& space) -> ErrorOr<FlatPtr> {
-        if (space->enforces_syscall_regions())
+        if (flags == to_underlying(VirtualMemoryRangeFlags::None))
+            return EINVAL;
+
+        if (space->enforces_syscall_regions() && (flags & to_underlying(VirtualMemoryRangeFlags::SyscallCode)))
             return EPERM;
 
         if (!address) {
@@ -584,10 +601,13 @@ ErrorOr<FlatPtr> Process::sys$annotate_mapping(Userspace<void*> address, int fla
 
         if (!region->is_mmap())
             return EINVAL;
+        if (region->is_immutable())
+            return EPERM;
 
-        if (flags == to_underlying(VirtualMemoryRangeFlags::None))
-            return EINVAL;
-        region->set_syscall_region(true);
+        if (flags & to_underlying(VirtualMemoryRangeFlags::SyscallCode))
+            region->set_syscall_region(true);
+        if (flags & to_underlying(VirtualMemoryRangeFlags::Immutable))
+            region->set_immutable();
         return 0;
     });
 }