This new flag controls two things:
- Whether the kernel will generate core dumps for the process
- Whether the EUID:EGID should own the process's files in /proc
Processes are automatically made non-dumpable when their EUID or EGID is
changed, either via syscalls that specifically modify those ID's, or via
sys$execve(), when a set-uid or set-gid program is executed.
A process can change its own dumpable flag at any time by calling the
new sys$prctl(PR_SET_DUMPABLE) syscall.
Fixes#4504.
We were casting the address to Userspace<T> without validating it first
which is no good and will trap an assertion soon after.
Let's catch this sooner with an ASSERT in the Userspace<T> constructor
and update the PT_PEEK and PT_POKE handlers to avoid it.
Fixes#4505.
It was possible to overwrite the entire EFLAGS register since we didn't
do any masking in the ptrace and sigreturn syscalls.
This made it trivial to gain IO privileges by raising IOPL to 3 and
then you could talk to hardware to do all kinds of nasty things.
Thanks to @allesctf for finding these issues! :^)
Their exploit/write-up: https://github.com/allesctf/writeups/blob/master/2020/hxpctf/wisdom2/writeup.md
This prevents zombies created by multi-threaded applications and brings
our model back to closer to what other OSs do.
This also means that SIGSTOP needs to halt all threads, and SIGCONT needs
to resume those threads.
This makes the Scheduler a lot leaner by not having to evaluate
block conditions every time it is invoked. Instead evaluate them as
the states change, and unblock threads at that point.
This also implements some more waitid/waitpid/wait features and
behavior. For example, WUNTRACED and WNOWAIT are now supported. And
wait will now not return EINTR when SIGCHLD is delivered at the
same time.
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 compiles, and contains exactly the same bugs as before.
The regex 'FIXME: PID/' should reveal all markers that I left behind, including:
- Incomplete conversion
- Issues or things that look fishy
- Actual bugs that will go wrong during runtime
We need to have a Thread lock to protect threading related
operations, such as Thread::m_blocker which is used in
Thread::block.
Also, if a Thread::Blocker indicates that it should be
unblocking immediately, don't actually block the Thread
and instead return immediately in Thread::block.
Output address validation should be done for the tracer's address space
and not the tracee's.
Also use copy_to_user() instead of copy_from_user(). The two are really
identical at the moment, but maybe we can add some assertions to make
sure we're doing what we think we're doing.
Thanks to Sergey for spotting these!
The syscall wrapper for ptrace needs to return the peeked value when
using PT_PEEK.
Because of this, the user has to check errno to detect an error in
PT_PEEK.
This commit changes the actual syscall's interface (only for PT_PEEK) to
allow the syscall wrapper to detect an error and change errno.
PT_SETTREGS sets the regsiters of the traced thread. It can only be
used when the tracee is stopped.
Also, refactor ptrace.
The implementation was getting long and cluttered the alraedy large
Process.cpp file.
This commit moves the bulk of the implementation to Kernel/Ptrace.cpp,
and factors out peek & poke to separate methods of the Process class.
