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Kernel: Make copy_to/from_user safe and remove unnecessary checks

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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.
This commit is contained in:
Tom 2020-09-11 21:11:07 -06:00 • committed by Andreas Kling
parent 7d1b8417bd
commit c8d9f1b9c9
149 changed files with 1585 additions and 1244 deletions
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112
Kernel/Process.h
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@ -362,111 +362,6 @@ public:
u32 m_ticks_in_user_for_dead_children { 0 };
u32 m_ticks_in_kernel_for_dead_children { 0 };
[[nodiscard]] bool validate_read_from_kernel(VirtualAddress, size_t) const;
[[nodiscard]] bool validate_read(const void*, size_t) const;
[[nodiscard]] bool validate_write(void*, size_t) const;
template<typename T>
[[nodiscard]] bool validate_read(Userspace<T*> ptr, size_t size) const
{
return validate_read(ptr.unsafe_userspace_ptr(), size);
}
template<typename T>
[[nodiscard]] bool validate_write(Userspace<T*> ptr, size_t size) const
{
return validate_write(ptr.unsafe_userspace_ptr(), size);
}
template<typename T>
[[nodiscard]] bool validate_read_typed(T* value, size_t count = 1)
{
Checked size = sizeof(T);
size *= count;
if (size.has_overflow())
return false;
return validate_read(value, size.value());
}
template<typename T>
[[nodiscard]] bool validate_read_typed(Userspace<T*> value, size_t count = 1)
{
Checked size = sizeof(T);
size *= count;
if (size.has_overflow())
return false;
return validate_read(value, size.value());
}
template<typename T>
[[nodiscard]] bool validate_read_and_copy_typed(T* dest, const T* src)
{
bool validated = validate_read_typed(src);
if (validated) {
copy_from_user(dest, src);
}
return validated;
}
template<typename T>
[[nodiscard]] bool validate_read_and_copy_typed(T* dest, Userspace<const T*> src)
{
bool validated = validate_read_typed(src);
if (validated) {
copy_from_user(dest, src);
}
return validated;
}
template<typename T>
[[nodiscard]] bool validate_read_and_copy_typed(T* dest, Userspace<T*> src)
{
Userspace<const T*> const_src { src.ptr() };
return validate_read_and_copy_typed(dest, const_src);
}
template<typename T>
[[nodiscard]] bool validate_write_typed(T* value, size_t count = 1)
{
Checked size = sizeof(T);
size *= count;
if (size.has_overflow())
return false;
return validate_write(value, size.value());
}
template<typename T>
[[nodiscard]] bool validate_write_typed(Userspace<T*> value, size_t count = 1)
{
Checked size = sizeof(T);
size *= count;
if (size.has_overflow())
return false;
return validate_write(value, size.value());
}
template<typename DataType, typename SizeType>
[[nodiscard]] bool validate(const Syscall::MutableBufferArgument<DataType, SizeType>& buffer)
{
return validate_write(buffer.data, buffer.size);
}
template<typename DataType, typename SizeType>
[[nodiscard]] bool validate(const Syscall::ImmutableBufferArgument<DataType, SizeType>& buffer)
{
return validate_read(buffer.data, buffer.size);
}
[[nodiscard]] String validate_and_copy_string_from_user(const char*, size_t) const;
[[nodiscard]] String validate_and_copy_string_from_user(Userspace<const char*> user_characters, size_t size) const
{
return validate_and_copy_string_from_user(user_characters.unsafe_userspace_ptr(), size);
}
[[nodiscard]] String validate_and_copy_string_from_user(const Syscall::StringArgument&) const;
Custody& current_directory();
Custody* executable()
{
@ -582,7 +477,7 @@ private:
void kill_all_threads();
int do_exec(NonnullRefPtr<FileDescription> main_program_description, Vector<String> arguments, Vector<String> environment, RefPtr<FileDescription> interpreter_description, Thread*& new_main_thread, u32& prev_flags);
ssize_t do_write(FileDescription&, const u8*, int data_size);
ssize_t do_write(FileDescription&, const UserOrKernelBuffer&, size_t);
KResultOr<NonnullRefPtr<FileDescription>> find_elf_interpreter_for_executable(const String& path, char (&first_page)[PAGE_SIZE], int nread, size_t file_size);
Vector<AuxiliaryValue> generate_auxiliary_vector() const;
@ -834,3 +729,8 @@ inline u32 Thread::effective_priority() const
} while (0)
}
inline static String copy_string_from_user(const Kernel::Syscall::StringArgument& string)
{
return copy_string_from_user(string.characters, string.length);
}