Kernel: Make copy_to/from_user safe and remove unnecessary checks

Since the CPU already does almost all necessary validation steps
for us, we don't really need to attempt to do this. Doing it
ourselves doesn't really work very reliably, because we'd have to
account for other processors modifying virtual memory, and we'd
have to account for e.g. pages not being able to be allocated
due to insufficient resources.

So change the copy_to/from_user (and associated helper functions)
to use the new safe_memcpy, which will return whether it succeeded
or not. The only manual validation step needed (which the CPU
can't perform for us) is making sure the pointers provided by user
mode aren't pointing to kernel mappings.

To make it easier to read/write from/to either kernel or user mode
data add the UserOrKernelBuffer helper class, which will internally
either use copy_from/to_user or directly memcpy, or pass the data
through directly using a temporary buffer on the stack.

Last but not least we need to keep syscall params trivial as we
need to copy them from/to user mode using copy_from/to_user.

1 files changed, 6 insertions, 6 deletions

diff --git a/Kernel/Devices/BlockDevice.h b/Kernel/Devices/BlockDevice.h
index 042a2cfce1..69786df3f8 100644
--- a/Kernel/Devices/BlockDevice.h
+++ b/Kernel/Devices/BlockDevice.h
@@ -37,13 +37,13 @@ public:
     size_t block_size() const { return m_block_size; }
     virtual bool is_seekable() const override { return true; }
 
-    bool read_block(unsigned index, u8*) const;
-    bool write_block(unsigned index, const u8*);
-    bool read_raw(u32 offset, unsigned length, u8*) const;
-    bool write_raw(u32 offset, unsigned length, const u8*);
+    bool read_block(unsigned index, UserOrKernelBuffer&) const;
+    bool write_block(unsigned index, const UserOrKernelBuffer&);
+    bool read_raw(u32 offset, unsigned length, UserOrKernelBuffer&) const;
+    bool write_raw(u32 offset, unsigned length, const UserOrKernelBuffer&);
 
-    virtual bool read_blocks(unsigned index, u16 count, u8*) = 0;
-    virtual bool write_blocks(unsigned index, u16 count, const u8*) = 0;
+    virtual bool read_blocks(unsigned index, u16 count, UserOrKernelBuffer&) = 0;
+    virtual bool write_blocks(unsigned index, u16 count, const UserOrKernelBuffer&) = 0;
 
 protected:
     BlockDevice(unsigned major, unsigned minor, size_t block_size = PAGE_SIZE)