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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
Notes: sideshowbarker 2024-07-19 02:42:35 +09:00
149 changed files with 1585 additions and 1244 deletions
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17
Kernel/Syscalls/execve.cpp
View file

@ -423,7 +423,8 @@ KResultOr<NonnullRefPtr<FileDescription>> Process::find_elf_interpreter_for_exec
return KResult(-ENOEXEC);
memset(first_page, 0, sizeof(first_page));
auto nread_or_error = interpreter_description->read((u8*)&first_page, sizeof(first_page));
auto first_page_buffer = UserOrKernelBuffer::for_kernel_buffer((u8*)&first_page);
auto nread_or_error = interpreter_description->read(first_page_buffer, sizeof(first_page));
if (nread_or_error.is_error())
return KResult(-ENOEXEC);
nread = nread_or_error.value();
@ -490,7 +491,8 @@ int Process::exec(String path, Vector<String> arguments, Vector<String> environm
// Read the first page of the program into memory so we can validate the binfmt of it
char first_page[PAGE_SIZE];
auto nread_or_error = description->read((u8*)&first_page, sizeof(first_page));
auto first_page_buffer = UserOrKernelBuffer::for_kernel_buffer((u8*)&first_page);
auto nread_or_error = description->read(first_page_buffer, sizeof(first_page));
if (nread_or_error.is_error())
return -ENOEXEC;
@ -554,7 +556,7 @@ int Process::sys$execve(Userspace<const Syscall::SC_execve_params*> user_params)
// NOTE: Be extremely careful with allocating any kernel memory in exec().
// On success, the kernel stack will be lost.
Syscall::SC_execve_params params;
if (!validate_read_and_copy_typed(&params, user_params))
if (!copy_from_user(&params, user_params))
return -EFAULT;
if (params.arguments.length > ARG_MAX || params.environment.length > ARG_MAX)
@ -574,13 +576,16 @@ int Process::sys$execve(Userspace<const Syscall::SC_execve_params*> user_params)
auto copy_user_strings = [this](const auto& list, auto& output) {
if (!list.length)
return true;
if (!validate_read_typed(list.strings, list.length))
Checked size = sizeof(list.length);
size *= list.length;
if (size.has_overflow())
return false;
Vector<Syscall::StringArgument, 32> strings;
strings.resize(list.length);
copy_from_user(strings.data(), list.strings.unsafe_userspace_ptr(), list.length * sizeof(Syscall::StringArgument));
if (!copy_from_user(strings.data(), list.strings, list.length * sizeof(Syscall::StringArgument)))
return false;
for (size_t i = 0; i < list.length; ++i) {
auto string = validate_and_copy_string_from_user(strings[i]);
auto string = copy_string_from_user(strings[i]);
if (string.is_null())
return false;
output.append(move(string));