Let's not be paying the function call overhead for these tiny ops.
Maybe there's an argument for having fewer gadgets in the kernel but
for now we're actually seeing stac() in profiles so let's put
that above theoretical security issues.
This was supposed to be the foundation for some kind of pre-kernel
environment, but nobody is working on it right now, so let's move
everything back into the kernel and remove all the confusion.
This patch adds PageFaultResponse::OutOfMemory which informs the fault
handler that we were unable to allocate a necessary physical page and
cannot continue.
In response to this, the kernel will crash the current process. Because
we are OOM, we can't symbolicate the crash like we normally would
(since the ELF symbolication code needs to allocate), so we also
communicate to Process::crash() that we're out of memory.
Now we can survive "allocate 300 MB" (only the allocate process dies.)
This is definitely not perfect and can easily end up killing a random
innocent other process who happened to allocate one page at the wrong
time, but it's a *lot* better than panicking on OOM. :^)
We currently only care about debug exceptions that are triggered
by the single-step execution mode.
The debug exception is translated to a SIGTRAP, which can be caught
and handled by the tracing thread.
Also, duplicate data in dbg() and klog() calls were removed.
In addition, leakage of virtual address to kernel log is prevented.
This is done by replacing kprintf() calls to dbg() calls with the
leaked data instead.
Also, other kprintf() calls were replaced with klog().
Now we use the GenericInterruptHandler class instead of IRQHandler in
the CPU functions.
This commit adds an include to the ISR stub macros header file.
Also, this commit adds support for IRQ sharing, so when an IRQHandler
will try to register to already-assigned IRQ number, a SharedIRQHandler
will be created to register both IRQHandlers.
We're not equipped to deal with page faults during an IRQ handler,
so add an assertion so we can immediately tell what's wrong.
This is why profiling sometimes hangs the system -- walking the stack
of the profiled thread causes a page fault and things fall apart.
Since we scrub both kmalloc() and kfree() with predictable values, we
can log a helpful message when hitting a crash that looks like it might
be a dereference of such scrubbed data.
System components that need an IRQ handling are now inheriting the
InterruptHandler class.
In addition to that, the initialization process of PATAChannel was
changed to fit the changes.
PATAChannel, E1000NetworkAdapter and RTL8139NetworkAdapter are now
inheriting from PCI::Device instead of InterruptHandler directly.
I noticed this while debugging a crash in backtrace generation.
If a process would crash while temporarily inspecting another process's
address space, the crashing thread would still use the other process's
page tables while handling the crash, causing all kinds of confusion
when trying to walk the stack of the crashing thread.
As suggested by Joshua, this commit adds the 2-clause BSD license as a
comment block to the top of every source file.
For the first pass, I've just added myself for simplicity. I encourage
everyone to add themselves as copyright holders of any file they've
added or modified in some significant way. If I've added myself in
error somewhere, feel free to replace it with the appropriate copyright
holder instead.
Going forward, all new source files should include a license header.
The kernel and its static data structures are no longer identity-mapped
in the bottom 8MB of the address space, but instead move above 3GB.
The first 8MB above 3GB are pseudo-identity-mapped to the bottom 8MB of
the physical address space. But things don't have to stay this way!
Thanks to Jesse who made an earlier attempt at this, it was really easy
to get device drivers working once the page tables were in place! :^)
Fixes#734.
It would be nice to do this in the assembly code, but we have to check
if the feature is available before doing a CLAC, so I've put this in
the C++ code for now.
Supervisor Mode Access Prevention (SMAP) is an x86 CPU feature that
prevents the kernel from accessing userspace memory. With SMAP enabled,
trying to read/write a userspace memory address while in the kernel
will now generate a page fault.
Since it's sometimes necessary to read/write userspace memory, there
are two new instructions that quickly switch the protection on/off:
STAC (disables protection) and CLAC (enables protection.)
These are exposed in kernel code via the stac() and clac() helpers.
There's also a SmapDisabler RAII object that can be used to ensure
that you don't forget to re-enable protection before returning to
userspace code.
THis patch also adds copy_to_user(), copy_from_user() and memset_user()
which are the "correct" way of doing things. These functions allow us
to briefly disable protection for a specific purpose, and then turn it
back on immediately after it's done. Going forward all kernel code
should be moved to using these and all uses of SmapDisabler are to be
considered FIXME's.
Note that we're not realizing the full potential of this feature since
I've used SmapDisabler quite liberally in this initial bring-up patch.
We now have these API's in <Kernel/Random.h>:
- get_fast_random_bytes(u8* buffer, size_t buffer_size)
- get_good_random_bytes(u8* buffer, size_t buffer_size)
- get_fast_random<T>()
- get_good_random<T>()
Internally they both use x86 RDRAND if available, otherwise they fall
back to the same LCG we had in RandomDevice all along.
The main purpose of this patch is to give kernel code a way to better
express its needs for random data.
Randomness is something that will require a lot more work, but this is
hopefully a step in the right direction.
This prevents code running outside of kernel mode from using the
following instructions:
* SGDT - Store Global Descriptor Table
* SIDT - Store Interrupt Descriptor Table
* SLDT - Store Local Descriptor Table
* SMSW - Store Machine Status Word
* STR - Store Task Register
There's no need for userspace to be able to use these instructions so
let's just disable them to prevent information leakage.
We now refuse to boot on machines that don't support PAE since all
of our paging code depends on it.
Also let's only enable SSE and PGE support if the CPU advertises it.
Instead of having a common entry point and looking at the PIC ISR to
figure out which IRQ we're servicing, just make a separate entryway
for each IRQ that pushes the IRQ number and jumps to a common routine.
This fixes a weird issue where incoming network packets would sometimes
cause the mouse to stop working. I didn't track it down further than
realizing we were sometimes EOI'ing the wrong IRQ.
Now that we have proper wait queues to drive waiter wakeup, we can use
the wake actions to break out of the scheduler's idle loop when we've
got a thread to run.
