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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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47
Kernel/Process.cpp
View file

@ -520,24 +520,6 @@ int Process::fd_flags(int fd) const
return -1;
}
String Process::validate_and_copy_string_from_user(const char* user_characters, size_t user_length) const
{
if (user_length == 0)
return String::empty();
if (!user_characters)
return {};
if (!validate_read(user_characters, user_length))
return {};
SmapDisabler disabler;
size_t measured_length = strnlen(user_characters, user_length);
return String(user_characters, measured_length);
}
String Process::validate_and_copy_string_from_user(const Syscall::StringArgument& string) const
{
return validate_and_copy_string_from_user(string.characters, string.length);
}
int Process::number_of_open_file_descriptors() const
{
int count = 0;
@ -602,27 +584,6 @@ siginfo_t Process::reap(Process& process)
return siginfo;
}
bool Process::validate_read_from_kernel(VirtualAddress vaddr, size_t size) const
{
if (vaddr.is_null())
return false;
return MM.validate_kernel_read(*this, vaddr, size);
}
bool Process::validate_read(const void* address, size_t size) const
{
if (!size)
return false;
return MM.validate_user_read(*this, VirtualAddress(address), size);
}
bool Process::validate_write(void* address, size_t size) const
{
if (!size)
return false;
return MM.validate_user_write(*this, VirtualAddress(address), size);
}
Custody& Process::current_directory()
{
if (!m_cwd)
@ -636,9 +597,10 @@ KResultOr<String> Process::get_syscall_path_argument(const char* user_path, size
return KResult(-EINVAL);
if (path_length > PATH_MAX)
return KResult(-ENAMETOOLONG);
if (!validate_read(user_path, path_length))
auto copied_string = copy_string_from_user(user_path, path_length);
if (copied_string.is_null())
return KResult(-EFAULT);
return copy_string_from_user(user_path, path_length);
return copied_string;
}
KResultOr<String> Process::get_syscall_path_argument(const Syscall::StringArgument& path) const
@ -659,7 +621,8 @@ void Process::finalize()
auto& description = description_or_error.value();
auto json = m_perf_event_buffer->to_json(m_pid, m_executable ? m_executable->absolute_path() : "");
// FIXME: Should this error path be surfaced somehow?
(void)description->write(json.data(), json.size());
auto json_buffer = UserOrKernelBuffer::for_kernel_buffer(json.data());
(void)description->write(json_buffer, json.size());
}
}