Kernel: Implement basic support for sys$mmap() with MAP_PRIVATE

You can now mmap a file as private and writable, and the changes you
make will only be visible to you.

This works because internally a MAP_PRIVATE region is backed by a
unique PrivateInodeVMObject instead of using the globally shared
SharedInodeVMObject like we always did before. :^)

Fixes #1045.

Kernel/Devices/BXVGADevice.cpp

@@ -166,9 +166,11 @@ u32 BXVGADevice::find_framebuffer_address()
     return framebuffer_address;
 }
 
-KResultOr<Region*> BXVGADevice::mmap(Process& process, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot)
+KResultOr<Region*> BXVGADevice::mmap(Process& process, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot, bool shared)
 {
     REQUIRE_PROMISE(video);
+    if (!shared)
+        return KResult(-ENODEV);
     ASSERT(offset == 0);
     ASSERT(size == framebuffer_size_in_bytes());
     auto vmobject = AnonymousVMObject::create_for_physical_range(m_framebuffer_address, framebuffer_size_in_bytes());

Kernel/Devices/BXVGADevice.h

@@ -41,7 +41,7 @@ public:
     BXVGADevice();
 
     virtual int ioctl(FileDescription&, unsigned request, unsigned arg) override;
-    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t, int prot) override;
+    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t, int prot, bool shared) override;
 
 private:
     virtual const char* class_name() const override { return "BXVGA"; }

Kernel/Devices/MBVGADevice.cpp

@@ -51,9 +51,11 @@ MBVGADevice::MBVGADevice(PhysicalAddress addr, int pitch, int width, int height)
     s_the = this;
 }
 
-KResultOr<Region*> MBVGADevice::mmap(Process& process, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot)
+KResultOr<Region*> MBVGADevice::mmap(Process& process, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot, bool shared)
 {
     REQUIRE_PROMISE(video);
+    if (!shared)
+        return KResult(-ENODEV);
     ASSERT(offset == 0);
     ASSERT(size == framebuffer_size_in_bytes());
     auto vmobject = AnonymousVMObject::create_for_physical_range(m_framebuffer_address, framebuffer_size_in_bytes());

Kernel/Devices/MBVGADevice.h

@@ -41,7 +41,7 @@ public:
     MBVGADevice(PhysicalAddress addr, int pitch, int width, int height);
 
     virtual int ioctl(FileDescription&, unsigned request, unsigned arg) override;
-    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t, int prot) override;
+    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t, int prot, bool shared) override;
 
 private:
     virtual const char* class_name() const override { return "MBVGA"; }

Kernel/FileSystem/File.cpp

@@ -54,7 +54,7 @@ int File::ioctl(FileDescription&, unsigned, unsigned)
     return -ENOTTY;
 }
 
-KResultOr<Region*> File::mmap(Process&, FileDescription&, VirtualAddress, size_t, size_t, int)
+KResultOr<Region*> File::mmap(Process&, FileDescription&, VirtualAddress, size_t, size_t, int, bool)
 {
     return KResult(-ENODEV);
 }

Kernel/FileSystem/File.h

@@ -77,7 +77,7 @@ public:
     virtual ssize_t read(FileDescription&, u8*, ssize_t) = 0;
     virtual ssize_t write(FileDescription&, const u8*, ssize_t) = 0;
     virtual int ioctl(FileDescription&, unsigned request, unsigned arg);
-    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot);
+    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot, bool shared);
 
     virtual String absolute_path(const FileDescription&) const = 0;
 

Kernel/FileSystem/FileDescription.cpp

@@ -281,10 +281,10 @@ InodeMetadata FileDescription::metadata() const
     return {};
 }
 
-KResultOr<Region*> FileDescription::mmap(Process& process, VirtualAddress vaddr, size_t offset, size_t size, int prot)
+KResultOr<Region*> FileDescription::mmap(Process& process, VirtualAddress vaddr, size_t offset, size_t size, int prot, bool shared)
 {
     LOCKER(m_lock);
-    return m_file->mmap(process, *this, vaddr, offset, size, prot);
+    return m_file->mmap(process, *this, vaddr, offset, size, prot, shared);
 }
 
 KResult FileDescription::truncate(u64 length)

Kernel/FileSystem/FileDescription.h

@@ -109,7 +109,7 @@ public:
     Custody* custody() { return m_custody.ptr(); }
     const Custody* custody() const { return m_custody.ptr(); }
 
-    KResultOr<Region*> mmap(Process&, VirtualAddress, size_t offset, size_t, int prot);
+    KResultOr<Region*> mmap(Process&, VirtualAddress, size_t offset, size_t, int prot, bool shared);
 
     bool is_blocking() const { return m_is_blocking; }
     void set_blocking(bool b) { m_is_blocking = b; }

Kernel/FileSystem/InodeFile.cpp

@@ -29,6 +29,7 @@
 #include <Kernel/FileSystem/InodeFile.h>
 #include <Kernel/FileSystem/VirtualFileSystem.h>
 #include <Kernel/Process.h>
+#include <Kernel/VM/PrivateInodeVMObject.h>
 #include <Kernel/VM/SharedInodeVMObject.h>
 
 namespace Kernel {
@@ -60,11 +61,18 @@ ssize_t InodeFile::write(FileDescription& description, const u8* data, ssize_t c
     return nwritten;
 }
 
-KResultOr<Region*> InodeFile::mmap(Process& process, FileDescription& description, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot)
+KResultOr<Region*> InodeFile::mmap(Process& process, FileDescription& description, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot, bool shared)
 {
     ASSERT(offset == 0);
     // FIXME: If PROT_EXEC, check that the underlying file system isn't mounted noexec.
-    auto* region = process.allocate_region_with_vmobject(preferred_vaddr, size, SharedInodeVMObject::create_with_inode(inode()), offset, description.absolute_path(), prot);
+    RefPtr<InodeVMObject> vmobject;
+    if (shared)
+        vmobject = SharedInodeVMObject::create_with_inode(inode());
+    else
+        vmobject = PrivateInodeVMObject::create_with_inode(inode());
+    if (!vmobject)
+        return KResult(-ENOMEM);
+    auto* region = process.allocate_region_with_vmobject(preferred_vaddr, size, *vmobject, offset, description.absolute_path(), prot);
     if (!region)
         return KResult(-ENOMEM);
     return region;

Kernel/FileSystem/InodeFile.h

@@ -49,7 +49,7 @@ public:
 
     virtual ssize_t read(FileDescription&, u8*, ssize_t) override;
     virtual ssize_t write(FileDescription&, const u8*, ssize_t) override;
-    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot) override;
+    virtual KResultOr<Region*> mmap(Process&, FileDescription&, VirtualAddress preferred_vaddr, size_t offset, size_t size, int prot, bool shared) override;
 
     virtual String absolute_path(const FileDescription&) const override;
 

Kernel/Process.cpp

@@ -321,19 +321,22 @@ static bool validate_mmap_prot(int prot, bool map_stack)
     return true;
 }
 
-static bool validate_inode_mmap_prot(const Process& process, int prot, const Inode& inode)
+static bool validate_inode_mmap_prot(const Process& process, int prot, const Inode& inode, bool map_shared)
 {
     auto metadata = inode.metadata();
-    if ((prot & PROT_WRITE) && !metadata.may_write(process))
-        return false;
     if ((prot & PROT_READ) && !metadata.may_read(process))
         return false;
-    InterruptDisabler disabler;
-    if (inode.shared_vmobject()) {
-        if ((prot & PROT_EXEC) && inode.shared_vmobject()->writable_mappings())
-            return false;
-        if ((prot & PROT_WRITE) && inode.shared_vmobject()->executable_mappings())
+
+    if (map_shared) {
+        if ((prot & PROT_WRITE) && !metadata.may_write(process))
             return false;
+        InterruptDisabler disabler;
+        if (inode.shared_vmobject()) {
+            if ((prot & PROT_EXEC) && inode.shared_vmobject()->writable_mappings())
+                return false;
+            if ((prot & PROT_WRITE) && inode.shared_vmobject()->executable_mappings())
+                return false;
+        }
     }
     return true;
 }
@@ -433,9 +436,6 @@ void* Process::sys$mmap(const Syscall::SC_mmap_params* user_params)
             return (void*)-EINVAL;
         if (static_cast<size_t>(offset) & ~PAGE_MASK)
             return (void*)-EINVAL;
-        // FIXME: Implement MAP_PRIVATE for FileDescription-backed mmap
-        if (map_private)
-            return (void*)-ENOTSUP;
         auto description = file_description(fd);
         if (!description)
             return (void*)-EBADF;
@@ -443,18 +443,20 @@ void* Process::sys$mmap(const Syscall::SC_mmap_params* user_params)
             return (void*)-ENODEV;
         if ((prot & PROT_READ) && !description->is_readable())
             return (void*)-EACCES;
-        if ((prot & PROT_WRITE) && !description->is_writable())
-            return (void*)-EACCES;
+        if (map_shared) {
+            if ((prot & PROT_WRITE) && !description->is_writable())
+                return (void*)-EACCES;
+        }
         if (description->inode()) {
-            if (!validate_inode_mmap_prot(*this, prot, *description->inode()))
+            if (!validate_inode_mmap_prot(*this, prot, *description->inode(), map_shared))
                 return (void*)-EACCES;
         }
-        auto region_or_error = description->mmap(*this, VirtualAddress(addr), static_cast<size_t>(offset), size, prot);
+        auto region_or_error = description->mmap(*this, VirtualAddress(addr), static_cast<size_t>(offset), size, prot, map_shared);
         if (region_or_error.is_error()) {
             // Fail if MAP_FIXED or address is 0, retry otherwise
             if (map_fixed || addr == 0)
                 return (void*)(int)region_or_error.error();
-            region_or_error = description->mmap(*this, {}, static_cast<size_t>(offset), size, prot);
+            region_or_error = description->mmap(*this, {}, static_cast<size_t>(offset), size, prot, map_shared);
         }
         if (region_or_error.is_error())
             return (void*)(int)region_or_error.error();
@@ -537,7 +539,7 @@ int Process::sys$mprotect(void* addr, size_t size, int prot)
         if (whole_region->access() == prot_to_region_access_flags(prot))
             return 0;
         if (whole_region->vmobject().is_inode()
-            && !validate_inode_mmap_prot(*this, prot, static_cast<const SharedInodeVMObject&>(whole_region->vmobject()).inode())) {
+            && !validate_inode_mmap_prot(*this, prot, static_cast<const SharedInodeVMObject&>(whole_region->vmobject()).inode(), whole_region->is_shared())) {
             return -EACCES;
         }
         whole_region->set_readable(prot & PROT_READ);
@@ -556,7 +558,7 @@ int Process::sys$mprotect(void* addr, size_t size, int prot)
         if (old_region->access() == prot_to_region_access_flags(prot))
             return 0;
         if (old_region->vmobject().is_inode()
-            && !validate_inode_mmap_prot(*this, prot, static_cast<const SharedInodeVMObject&>(old_region->vmobject()).inode())) {
+            && !validate_inode_mmap_prot(*this, prot, static_cast<const SharedInodeVMObject&>(old_region->vmobject()).inode(), old_region->is_shared())) {
             return -EACCES;
         }