Before we start disabling acquisition of the big process lock for
specific syscalls, make sure to document and assert that all the
lock is held during all syscalls.
Thread::yield_and_release_relock_big_lock releases the big lock, yields
and then relocks the big lock.
Thread::yield_assuming_not_holding_big_lock yields assuming the big
lock is not being held.
This was an old SerenityOS-specific syscall for donating the remainder
of the calling thread's time-slice to another thread within the same
process.
Now that Threading::Lock uses a pthread_mutex_t internally, we no
longer need this syscall, which allows us to get rid of a surprising
amount of unnecessary scheduler logic. :^)
The Process::Handler type has KResultOr<FlatPtr> as its return type.
Using a different return type with an equally-sized template parameter
sort of works but breaks once that condition is no longer true, e.g.
for KResultOr<int> on x86_64.
Ideally the syscall handlers would also take FlatPtrs as their args
so we can get rid of the reinterpret_cast for the function pointer
but I didn't quite feel like cleaning that up as well.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
Process member variable like m_euid are very valuable targets for
kernel exploits and until now they have been writable at all times.
This patch moves m_euid along with a whole bunch of other members
into a new Process::ProtectedData struct. This struct is remapped
as read-only memory whenever we don't need to write to it.
This means that a kernel write primitive is no longer enough to
overwrite a process's effective UID, you must first unprotect the
protected data where the UID is stored. :^)
The priority boosting mechanism has been broken for a very long time.
Let's remove it from the codebase and we can bring it back the day
someone feels like implementing it in a working way. :^)
We need to account for how many shared lock instances the current
thread owns, so that we can properly release such references when
yielding execution.
We also need to release the process lock when donating.
Similar to Process, we need to make Thread refcounted. This will solve
problems that will appear once we schedule threads on more than one
processor. This allows us to hold onto threads without necessarily
holding the scheduler lock for the entire duration.
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.
By making the Process class RefCounted we don't really need
ProcessInspectionHandle anymore. This also fixes some race
conditions where a Process may be deleted while still being
used by ProcFS.
Also make sure to acquire the Process' lock when accessing
regions.
Last but not least, there's no reason why a thread can't be
scheduled while being inspected, though in practice it won't
happen anyway because the scheduler lock is held at the same
time.
Note: I switched from copying the single element out of the sched_param
struct, to copy struct it self as it is identical in functionality.
This way the types match up nicer with the Userpace<T> api's and it
conforms to the conventions used in other syscalls.
This is something I've been meaning to do for a long time, and here we
finally go. This patch moves all sys$foo functions out of Process.cpp
and into files in Kernel/Syscalls/.
It's not exactly one syscall per file (although it could be, but I got
a bit tired of the repetitive work here..)
This makes hacking on individual syscalls a lot less painful since you
don't have to rebuild nearly as much code every time. I'm also hopeful
that this makes it easier to understand individual syscalls. :^)
