Previously, the instruction fetch flag of the page fault handler
did not have the currect binary representation, and would always
return false. This aligns these flags.
Because registering and unregistering interrupt handlers triggers
calls to virtual functions, we can't do this in the constructor
and destructor.
Fixes#5539
This was necessary in the past when crash handling would modify
various global things, but all that stuff is long gone so we can
simplify crashes by leaving the interrupt flag alone.
Make more of the kernel compile in 64-bit mode, and make some things
pointer-size-agnostic (by using FlatPtr.)
There's a lot of work to do here before the kernel will even compile.
We were only 448 KiB away from filling up the old slot size we reserve
for the kernel above the 3 GiB mark. This expands the slot to 16 MiB,
which allows us to continue booting the kernel until somebody takes
the time to improve our loader.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
When building the kernel with -O2, we somehow ended up with the kernel
command line outside of the lower 8MB of physical memory. Since we don't
map that area in our initial page table setup, we would triple fault
when trying to parse the command line.
This patch sidesteps the issue by copying the (first 4KB of) the kernel
command line to a buffer in a known safe location at boot.
We want to make sure these functions actually do get unmapped. If they
were inlined somewhere, the inlined version(s) would remain mapped.
Thanks to "thislooksfun" for the suggestion! :^)
There's no real system here, I just added it to various functions
that I don't believe we ever want to call after initialization
has finished.
With these changes, we're able to unmap 60 KiB of kernel text
after init. :^)
You can now declare functions with UNMAP_AFTER_INIT and they'll get
segregated into a separate kernel section that gets completely
unmapped at the end of initialization.
This can be used for anything we don't need to call once we've booted
into userspace.
There are two nice things about this mechanism:
- It allows us to free up entire pages of memory for other use.
(Note that this patch does not actually make use of the freed
pages yet, but in the future we totally could!)
- It allows us to get rid of obviously dangerous gadgets like
write-to-CR0 and write-to-CR4 which are very useful for an attacker
trying to disable SMAP/SMEP/etc.
I've also made sure to include a helpful panic message in case you
hit a kernel crash because of this protection. :^)
You can now use the READONLY_AFTER_INIT macro when declaring a variable
and we will put it in a special ".ro_after_init" section in the kernel.
Data in that section remains writable during the boot and init process,
and is then marked read-only just before launching the SystemServer.
This is based on an idea from the Linux kernel. :^)
Since kernel stacks are much smaller (64 KiB) than userspace stacks,
we only add a small bit of randomness here (0-256 bytes, 16b aligned.)
This makes the location of the task context switch buffer not be
100% predictable. Note that we still also add extra randomness upon
syscall entry, so this patch primarily affects context switching.
If we try to align a number above 0xfffff000 to the next multiple of
the page size (4 KiB), it would wrap around to 0. This is most likely
never what we want, so let's assert if that happens.
If we're flushing user space pointers and the process only has one
thread, we do not need to broadcast this to other processors as
they will all discard that request anyway.
Attempt to wake idle processors to get threads to be scheduled more quickly.
We don't want to wait until the next timer tick if we have processors that
aren't doing anything.
This eliminates the window between calling Processor::current and
the member function where a thread could be moved to another
processor. This is generally not as big of a concern as with
Processor::current_thread, but also slightly more light weight.
Change Thread::current to be a static function and read using the fs
register, which eliminates a window between Processor::current()
returning and calling a function on it, which can trigger preemption
and a move to a different processor, which then causes operating
on the wrong object.
We also need to store m_in_critical in the Thread upon switching,
and we need to restore it. This solves a problem where threads
moving between different processors could end up with an unexpected
value.
This allows us to determine what the previous mode (user or kernel)
was, e.g. in the timer interrupt. This is used e.g. to determine
whether a signal handler should be set up.
Fixes#5096
We were enabling interrupts too early, before the first context switch to
a thread was complete. This could then trigger another context switch
within the context switch, which lead to a crash.
This was done with the help of several scripts, I dump them here to
easily find them later:
awk '/#ifdef/ { print "#cmakedefine01 "$2 }' AK/Debug.h.in
for debug_macro in $(awk '/#ifdef/ { print $2 }' AK/Debug.h.in)
do
find . \( -name '*.cpp' -o -name '*.h' -o -name '*.in' \) -not -path './Toolchain/*' -not -path './Build/*' -exec sed -i -E 's/#ifdef '$debug_macro'/#if '$debug_macro'/' {} \;
done
# Remember to remove WRAPPER_GERNERATOR_DEBUG from the list.
awk '/#cmake/ { print "set("$2" ON)" }' AK/Debug.h.in
Booting old computers without RDRAND/RDSEED and without a disk makes
the system severely starved for entropy. Uses interrupts as a source
to side-step that issue.
Also warn whenever the system is starved of entropy, because that's
a non-obvious failure mode.
