While I was updating syscalls to stop passing null-terminated strings,
I added some helpful struct types:
- StringArgument { const char*; size_t; }
- ImmutableBuffer<Data, Size> { const Data*; Size; }
- MutableBuffer<Data, Size> { Data*; Size; }
The Process class has some convenience functions for validating and
optionally extracting the contents from these structs:
- get_syscall_path_argument(StringArgument)
- validate_and_copy_string_from_user(StringArgument)
- validate(ImmutableBuffer)
- validate(MutableBuffer)
There's still so much code around this and I'm wondering if we should
generate most of it instead. Possible nice little project.
In order to preserve the absolute path of the process root, we save the
custody used by chroot() before stripping it to become the new "/".
There's probably a better way to do this.
The chroot() syscall now allows the superuser to isolate a process into
a specific subtree of the filesystem. This is not strictly permanent,
as it is also possible for a superuser to break *out* of a chroot, but
it is a useful mechanism for isolating unprivileged processes.
The VFS now uses the current process's root_directory() as the root for
path resolution purposes. The root directory is stored as an uncached
Custody in the Process object.
Note that I'm developing some helper types in the Syscall namespace as
I go here. Once I settle on some nice types, I will convert all the
other syscalls to use them as well.
The userspace execve() wrapper now measures all the strings and puts
them in a neat and tidy structure on the stack.
This way we know exactly how much to copy in the kernel, and we don't
have to use the SMAP-violating validate_read_str(). :^)
When loading a new executable, we now map the ELF image in kernel-only
memory and parse it there. Then we use copy_to_user() when initializing
writable regions with data from the executable.
Note that the exec() syscall still disables SMAP protection and will
require additional work. This patch only affects kernel-originated
process spawns.
This encourages callers to strongly reference file descriptions while
working with them.
This fixes a use-after-free issue where one thread would close() an
open fd while another thread was blocked on it becoming readable.
Test: Kernel/uaf-close-while-blocked-in-read.cpp
This code never worked, as was never used for anything. We can build
a much better SHM implementation on top of TmpFS or similar when we
get to the point when we need one.
Split a region into two/three if the desired mprotect range is a strict
subset of an existing region. We can then set the access bits on a new
region that is just our desired range and add both the new
desired subregion and the leftovers back to our page tables.
This patch introduces a syscall:
int set_thread_boost(int tid, int amount)
You can use this to add a permanent boost value to the effective thread
priority of any thread with your UID (or any thread in the system if
you are the superuser.)
This is quite crude, but opens up some interesting opportunities. :^)
Threads now have numeric priorities with a base priority in the 1-99
range.
Whenever a runnable thread is *not* scheduled, its effective priority
is incremented by 1. This is tracked in Thread::m_extra_priority.
The effective priority of a thread is m_priority + m_extra_priority.
When a runnable thread *is* scheduled, its m_extra_priority is reset to
zero and the effective priority returns to base.
This means that lower-priority threads will always eventually get
scheduled to run, once its effective priority becomes high enough to
exceed the base priority of threads "above" it.
The previous values for ThreadPriority (Low, Normal and High) are now
replaced as follows:
Low -> 10
Normal -> 30
High -> 50
In other words, it will take 20 ticks for a "Low" priority thread to
get to "Normal" effective priority, and another 20 to reach "High".
This is not perfect, and I've used some quite naive data structures,
but I think the mechanism will allow us to build various new and
interesting optimizations, and we can figure out better data structures
later on. :^)
This is memory that's loaded from an inode (file) but not modified in
memory, so still identical to what's on disk. This kind of memory can
be freed and reloaded transparently from disk if needed.
Dirty private memory is all memory in non-inode-backed mappings that's
process-private, meaning it's not shared with any other process.
This patch exposes that number via SystemMonitor, giving us an idea of
how much memory each process is responsible for all on its own.
We don't care about dead processes that were once members of a specific
process group.
This was causing us to try and send SIGINT to already-dead processes
when pressing Ctrl+C in a terminal whose pgrp they were once in.
Fixes#922.
This patch implements a simple version of the futex (fast userspace
mutex) API in the kernel and uses it to make the pthread_cond_t API's
block instead of busily sched_yield().
An arbitrary userspace address is passed to the kernel as a "token"
that identifies the futex and you can then FUTEX_WAIT and FUTEX_WAKE
that specific userspace address.
FUTEX_WAIT corresponds to pthread_cond_wait() and FUTEX_WAKE is used
for pthread_cond_signal() and pthread_cond_broadcast().
I'm pretty sure I'm missing something in this implementation, but it's
hopefully okay for a start. :^)
This is a little strange, but it's how I understand things should work.
The first thread in a new process now has TID == PID.
Additional threads subsequently spawned in that process all have unique
TID's generated by the PID allocator. TIDs are now globally unique.
The idea of all processes reliably having a main thread was nice in
some ways, but cumbersome in others. More importantly, it didn't match
up with POSIX thread semantics, so let's move away from it.
This thread gets rid of Process::main_thread() and you now we just have
a bunch of Thread objects floating around each Process.
When the finalizer nukes the last Thread in a Process, it will also
tear down the Process.
There's a bunch of more things to fix around this, but this is where we
get started :^)
This patch adds a single "kernel info page" that is mappable read-only
by any process and contains the current time of day.
This is then used to implement a version of gettimeofday() that doesn't
have to make a syscall.
To protect against race condition issues, the info page also has a
serial number which is incremented whenever the kernel updates the
contents of the page. Make sure to verify that the serial number is the
same before and after reading the information you want from the page.
The kernel now supports basic profiling of all the threads in a process
by calling profiling_enable(pid_t). You finish the profiling by calling
profiling_disable(pid_t).
This all works by recording thread stacks when the timer interrupt
fires and the current thread is in a process being profiled.
Note that symbolication is deferred until profiling_disable() to avoid
adding more noise than necessary to the profile.
A simple "/bin/profile" command is included here that can be used to
start/stop profiling like so:
$ profile 10 on
... wait ...
$ profile 10 off
After a profile has been recorded, it can be fetched in /proc/profile
There are various limits (or "bugs") on this mechanism at the moment:
- Only one process can be profiled at a time.
- We allocate 8MB for the samples, if you use more space, things will
not work, and probably break a bit.
- Things will probably fall apart if the profiled process dies during
profiling, or while extracing /proc/profile
This patch makes SharedBuffer use a PurgeableVMObject as its underlying
memory object.
A new syscall is added to control the volatile flag of a SharedBuffer.
