Using the kernel stack is preferable, especially when the examined
strings should be limited to a reasonable length.
This is a small improvement, because if we don't actually move these
strings then we don't need to own heap allocations for them during the
syscall handler function scope.
In addition to that, some kernel strings are known to be limited, like
the hostname string, for these strings we also can use FixedStringBuffer
to store and copy to and from these buffers, without using any heap
allocations at all.
Instead, use the FixedCharBuffer class to ensure we always use a static
buffer storage for these names. This ensures that if a Process or a
Thread were created, there's a guarantee that setting a new name will
never fail, as only copying of strings should be done to that static
storage.
The limits which are set are 32 characters for processes' names and 64
characters for thread names - this is because threads' names could be
more verbose than processes' names.
For a long time, our shutdown procedure has basically been:
- Acquire big process lock.
- Switch framebuffer to Kernel debug console.
- Sync and lock all file systems so that disk caches are flushed and
files are in a good state.
- Use firmware and architecture-specific functionality to perform
hardware shutdown.
This naive and simple shutdown procedure has multiple issues:
- No processes are terminated properly, meaning they cannot perform more
complex cleanup work. If they were in the middle of I/O, for instance,
only the data that already reached the Kernel is written to disk, and
data corruption due to unfinished writes can therefore still occur.
- No file systems are unmounted, meaning that any important unmount work
will never happen. This is important for e.g. Ext2, which has
facilites for detecting improper unmounts (see superblock's s_state
variable) and therefore requires a proper unmount to be performed.
This was also the starting point for this PR, since I wanted to
introduce basic Ext2 file system checking and unmounting.
- No hardware is properly shut down beyond what the system firmware does
on its own.
- Shutdown is performed within the write() call that asked the Kernel to
change its power state. If the shutdown procedure takes longer (i.e.
when it's done properly), this blocks the process causing the shutdown
and prevents any potentially-useful interactions between Kernel and
userland during shutdown.
In essence, current shutdown is a glorified system crash with minimal
file system cleanliness guarantees.
Therefore, this commit is the first step in improving our shutdown
procedure. The new shutdown flow is now as follows:
- From the write() call to the power state SysFS node, a new task is
started, the Power State Switch Task. Its only purpose is to change
the operating system's power state. This task takes over shutdown and
reboot duties, although reboot is not modified in this commit.
- The Power State Switch Task assumes that userland has performed all
shutdown duties it can perform on its own. In particular, it assumes
that all kinds of clean process shutdown have been done, and remaining
processes can be hard-killed without consequence. This is an important
separation of concerns: While this commit does not modify userland, in
the future SystemServer will be responsible for performing proper
shutdown of user processes, including timeouts for stubborn processes
etc.
- As mentioned above, the task hard-kills remaining user processes.
- The task hard-kills all Kernel processes except itself and the
Finalizer Task. Since Kernel processes can delay their own shutdown
indefinitely if they want to, they have plenty opportunity to perform
proper shutdown if necessary. This may become a problem with
non-cooperative Kernel tasks, but as seen two commits earlier, for now
all tasks will cooperate within a few seconds.
- The task waits for the Finalizer Task to clean up all processes.
- The task hard-kills and finalizes the Finalizer Task itself, meaning
that it now is the only remaining process in the system.
- The task syncs and locks all file systems, and then unmounts them. Due
to an unknown refcount bug we currently cannot unmount the root file
system; therefore the task is able to abort the clean unmount if
necessary.
- The task performs platform-dependent hardware shutdown as before.
This commit has multiple remaining issues (or exposed existing ones)
which will need to be addressed in the future but are out of scope for
now:
- Unmounting the root filesystem is impossible due to remaining
references to the inodes /home and /home/anon. I investigated this
very heavily and could not find whoever is holding the last two
references.
- Userland cannot perform proper cleanup, since the Kernel's power state
variable is accessed directly by tools instead of a proper userland
shutdown procedure directed by SystemServer.
The recently introduced Firmware/PowerState procedures are removed
again, since all of the architecture-independent code can live in the
power state switch task. The architecture-specific code is kept,
however.
Once we move to a more proper shutdown procedure, processes other than
the finalizer task must be able to perform cleanup and finalization
duties, not only because the finalizer task itself needs to be cleaned
up by someone. This global variable, mirroring the early boot flags,
allows a future shutdown process to perform cleanup on its own.
Note that while this *could* be considered a weakening in security, the
attack surface is minimal and the results are not dramatic. To exploit
this, an attacker would have to gain a Kernel write primitive to this
global variable (bypassing KASLR among other things) and then gain some
way of calling the relevant functions, all of this only to destroy some
other running process. The same effect can be achieved with LPE which
can often be gained with significantly simpler userspace exploits (e.g.
of setuid binaries).
Since we never check a kernel process's state like a userland process,
it's possible for a kernel process to ignore the fact that someone is
trying to kill it, and continue running. This is not desireable if we
want to properly shutdown all processes, including Kernel ones.
Previously, we started parsing the ELF file again in a completely
different place, and without the partial mapping that we do while
validating.
Instead of doing manual parsing in two places, just capture the
requested stack size right after we validated it.
This is a preparation before we can create a usable mechanism to use
filesystem-specific mount flags.
To keep some compatibility with userland code, LibC and LibCore mount
functions are kept being usable, but now instead of doing an "atomic"
syscall, they do multiple syscalls to perform the complete procedure of
mounting a filesystem.
The FileBackedFileSystem IntrusiveList in the VFS code is now changed to
be protected by a Mutex, because when we mount a new filesystem, we need
to check if a filesystem is already created for a given source_fd so we
do a scan for that OpenFileDescription in that list. If we fail to find
an already-created filesystem we create a new one and register it in the
list if we successfully mounted it. We use a Mutex because we might need
to initiate disk access during the filesystem creation, which will take
other mutexes in other parts of the kernel, therefore making it not
possible to take a spinlock while doing this.
Once LibC is installed to the sysroot and its conflicts with libc++
are resolved, including LibC headers in such a way will cause errors
with a modern LLVM-based toolchain.
This is needed to avoid including LibC headers in Lagom builds.
Unfortunately, we cannot rely on the build machine to provide a
fully POSIX-compatible ELF header for Lagom builds, so we have to
use our own.
These 4 fields were made `Atomic` in
c3f668a758, at which time these were still
accessed unserialized and TOCTOU bugs could happen. Later, in
8ed06ad814, we serialized access to these
fields in a number of helper methods, removing the need for `Atomic`.
This has KString, KBuffer, DoubleBuffer, KBufferBuilder, IOWindow,
UserOrKernelBuffer and ScopedCritical classes being moved to the
Kernel/Library subdirectory.
Also, move the panic and assertions handling code to that directory.
That's what this class really is; in fact that's what the first line of
the comment says it is.
This commit does not rename the main files, since those will contain
other time-related classes in a little bit.
- Instead of taking the first new thread as an out-parameter, we now
bundle the process and its first thread in a struct and use that
as the return value.
- Make all Process factory functions return ErrorOr. Use this to convert
some places to more TRY().
- Drop the "try_" prefix on Process factory functions.
Until now, our kernel has reimplemented a number of AK classes to
provide automatic internal locking:
- RefPtr
- NonnullRefPtr
- WeakPtr
- Weakable
This patch renames the Kernel classes so that they can coexist with
the original AK classes:
- RefPtr => LockRefPtr
- NonnullRefPtr => NonnullLockRefPtr
- WeakPtr => LockWeakPtr
- Weakable => LockWeakable
The goal here is to eventually get rid of the Lock* classes in favor of
using external locking.
Each of these strings would previously rely on StringView's char const*
constructor overload, which would call __builtin_strlen on the string.
Since we now have operator ""sv, we can replace these with much simpler
versions. This opens the door to being able to remove
StringView(char const*).
No functional changes.
This change unifies the naming convention for kernel tasks.
The goal of this change is to:
- Make the task names more descriptive, so users can more
easily understand their purpose in System Monitor.
- Unify the naming convention so they are consistent.
With -Og, all calls to create_kernel_process were triggering -Wnonnull
when creating these lambdas that get implicitly converted to function
pointers. A different design of create_kernel_process to use
AK::Function instead might avoid this awkward behavior.
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 *
This commit is very invasive, because Thread likes to take a pointer and write
to it. This means that translating between timespec/timeval/Time would have been
more difficult than just changing everything that hands a raw pointer to Thread,
in bulk.
In preparation for marking BlockingResult [[nodiscard]], there are a few
places that perform infinite waits, which we never observe the result of
the wait. Instead of suppressing them, add an alternate function which
returns void when performing and infinite wait.
Problem:
- Many constructors are defined as `{}` rather than using the ` =
default` compiler-provided constructor.
- Some types provide an implicit conversion operator from `nullptr_t`
instead of requiring the caller to default construct. This violates
the C++ Core Guidelines suggestion to declare single-argument
constructors explicit
(https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c46-by-default-declare-single-argument-constructors-explicit).
Solution:
- Change default constructors to use the compiler-provided default
constructor.
- Remove implicit conversion operators from `nullptr_t` and change
usage to enforce type consistency without conversion.
These changes are arbitrarily divided into multiple commits to make it
easier to find potentially introduced bugs with git bisect.Everything:
The modifications in this commit were automatically made using the
following command:
find . -name '*.cpp' -exec sed -i -E 's/dbg\(\) << ("[^"{]*");/dbgln\(\1\);/' {} \;
Fix some problems with join blocks where the joining thread block
condition was added twice, which lead to a crash when trying to
unblock that condition a second time.
Deferred block condition evaluation by File objects were also not
properly keeping the File object alive, which lead to some random
crashes and corruption problems.
Other problems were caused by the fact that the Queued state didn't
handle signals/interruptions consistently. To solve these issues we
remove this state entirely, along with Thread::wait_on and change
the WaitQueue into a BlockCondition instead.
Also, deliver signals even if there isn't going to be a context switch
to another thread.
Fixes#4336 and #4330
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.
This adds the ability to pass a pointer to kernel thread/process.
Also add the ability to use a closure as thread function, which
allows passing information to a kernel thread more easily.
Use the TimerQueue to expire blocking operations, which is one less thing
the Scheduler needs to check on every iteration.
Also, add a BlockTimeout class that will automatically handle relative or
absolute timeouts as well as overriding timeouts (e.g. socket timeouts)
more consistently.
Also, rework the TimerQueue class to be able to fire events from
any processor, which requires Timer to be RefCounted. Also allow
creating id-less timers for use by blocking operations.
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.
The Lock class still permits no reason, but for everything else
require a reason to be passed to Thread::wait_on. This makes it
easier to diagnose why a Thread is in Queued state.
