This ensures that both mutable and immutable access to the protected
data of a process is serialized.
Note that there may still be multiple TOCTOU issues around this, as we
have a bunch of convenience accessors that make it easy to introduce
them. We'll need to audit those as well.
This matches out general macro use, and specifically other verification
macros like VERIFY(), VERIFY_NOT_REACHED(), VERIFY_INTERRUPTS_ENABLED(),
and VERIFY_INTERRUPTS_DISABLED().
Previously we would crash the process immediately when a promise
violation was found during a syscall. This is error prone, as we
don't unwind the stack. This means that in certain cases we can
leak resources, like an OwnPtr / RefPtr tracked on the stack. Or
even leak a lock acquired in a ScopeLockLocker.
To remedy this situation we move the promise violation handling to
the syscall handler, right before we return to user space. This
allows the code to follow the normal unwind path, and grantees
there is no longer any cleanup that needs to occur.
The Process::require_promise() and Process::require_no_promises()
functions were modified to return ErrorOr<void> so we enforce that
the errors are always propagated by the caller.
This change lays the foundation for making the require_promise return
an error hand handling the process abort outside of the syscall
implementations, to avoid cases where we would leak resources.
It also has the advantage that it makes removes a gs pointer read
to look up the current thread, then process for every syscall. We
can instead go through the Process this pointer in most cases.
We now use AK::Error and AK::ErrorOr<T> in both kernel and userspace!
This was a slightly tedious refactoring that took a long time, so it's
not unlikely that some bugs crept in.
Nevertheless, it does pass basic functionality testing, and it's just
real nice to finally see the same pattern in all contexts. :^)
This patch replaces the remaining users of this API with the new
try_copy_kstring_from_user() instead. Note that we still convert to a
String for continued processing, and I've added FIXME about continuing
work on using KString all the way.
The compiler can re-order the structure (class) members if that's
necessary, so if we make Process to inherit from ProcFSExposedComponent,
even if the declaration is to inherit first from ProcessBase, then from
ProcFSExposedComponent and last from Weakable<Process>, the members of
class ProcFSExposedComponent (including the Ref-counted parts) are the
first members of the Process class.
This problem made it impossible to safely use the current toggling
method with the write-protection bit on the ProcessBase members, so
instead of inheriting from it, we make its members the last ones in the
Process class so we can safely locate and modify the corresponding page
write protection bit of these values.
We make sure that the Process class doesn't expand beyond 8192 bytes and
the protected values are always aligned on a page boundary.
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.
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 *
The previous architecture had a huge flaw: the pointer to the protected
data was itself unprotected, allowing you to overwrite it at any time.
This patch reorganizes the protected data so it's part of the Process
class itself. (Actually, it's a new ProcessBase helper class.)
We use the first 4 KB of Process objects themselves as the new storage
location for protected data. Then we make Process objects page-aligned
using MAKE_ALIGNED_ALLOCATED.
This allows us to easily turn on/off write-protection for everything in
the ProcessBase portion of Process. :^)
Thanks to @bugaevc for pointing out the flaw! This is still not perfect
but it's an improvement.
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. :^)
All users of this mechanism have been switched to anonymous files and
passing file descriptors with sendfd()/recvfd().
Shbufs got us where we are today, but it's time we say good-bye to them
and welcome a much more idiomatic replacement. :^)
This was a goofy kernel API where you could assign an icon_id (int) to
a process which referred to a global shbuf with a 16x16 icon bitmap
inside it.
Instead of this, programs that want to display a process icon now
retrieve it from the process executable instead.
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
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. :^)
