This commit moves the length calculations out to be directly on the
StringView users. This is an important step towards the goal of removing
StringView(char const*), as it moves the responsibility of calculating
the size of the string to the user of the StringView (which will prevent
naive uses causing OOB access).
Access to RDTSC is occasionally restricted to give malware one less
option to accurately time attacks (side-channels, etc.).
However, QEMU requires access to the timestamp counter for the exact
same reason (which is accurately timing its CPU ticks), so lets just
enable it for now.
The RDGSBASE userspace instruction allows programs to read the contents
of the gs segment register which contains a kernel pointer to the base
of the current Processor struct.
Since we don't use this instruction in Serenity at the moment, we can
simply disable it for now to ensure we don't break KASLR. Support can
later be restored once proper swapping of the contents of gs is done on
userspace/kernel boundaries.
This requires us to add an Interrupts.h file in the Kernel/Arch
directory, which includes the architecture specific files.
The commit also stubs out the functions to be able to compile the
aarch64 Kernel.
This adds some new buffers to the `FPUState` struct, which contains
enough space for the `xsave` instruction to run. This instruction writes
the upper part of the x86 SIMD registers (YMM0-15) to a seperate
256-byte area, as well as an "xsave header" describing the region.
If the underlying processor supports AVX, the `fxsave` instruction is no
longer used, as `xsave` itself implictly saves all of the SSE and x87
registers.
Co-authored-by: Leon Albrecht <leon.a@serenityos.org>
We're now able to detect all the regular CPUID feature flags from
ECX/EDX for EAX=1 :^)
None of the new ones are being used for anything yet, but they will show
up in /proc/cpuinfo and subsequently lscpu and SystemMonitor.
Note that I replaced the periods from the SSE 4.1 and 4.2 instructions
with underscores, which matches the internal enum names, Linux's
/proc/cpuinfo and the general pattern of replacing special characters
with underscores to limit feature names to [a-z0-9_].
The enum member stringification has been moved to a new function for
better re-usability and to avoid cluttering up Processor.cpp.
This will make it possible to add many, many more CPU features - more
than the current limit 32 and later limit of 64 if we stick with an enum
class to be specific :^)
Checks of ECX go before EDX, and the bit indices are now ordered
properly. Additionally, handling of the EDX[11] bit has been moved into
a lambda function to keep the series of if statements neatly together.
All of this makes it *a lot* easier to follow along and compare the
implementation to the tables in the Intel manual, e.g. to find missing
checks.
Function-local `static constexpr` variables can be `constexpr`. This
can reduce memory consumption, binary size, and offer additional
compiler optimizations.
These changes result in a stripped x86_64 kernel binary size reduction
of 592 bytes.
Move this architecture-specific sanity check (IOPL must be 0) out of
Scheduler and into the x86 enter_thread_context(). Also do this for
every thread and not just userspace ones.
It was annoyingly hard to spot these when we were using them with
different amounts of qualification everywhere.
This patch uses Thread::State::Foo everywhere instead of Thread::Foo
or just Foo.
Signal dispatch is already taken care of elsewhere, so there appears to
be no need for the hack in enter_current().
This also allows us to remove the Thread::m_in_block flag, simplifying
thread blocking logic somewhat.
Verified with the original repro for #4336 which this was meant to fix.
This allows us to enable Write-Combine on e.g. framebuffers,
significantly improving performance on bare metal.
To keep things simple we right now only use one of up to three bits
(bit 7 in the PTE), which maps to the PA4 entry in the PAT MSR, which
we set to the Write-Combine mode on each CPU at boot time.
Since the inline capacity of the Vector return type was not specified
explicitly, the vector was automatically copied to a 0-length inline
capacity one, essentially eliminating the optimization.
Contradictory to the comment above it, this while loop was actually
clearing the selectors above or equal to the edited one (instead of
the selectors that were skipped when the gdt was extended), this wasn't
really an issue so far, as all calls to this function did extend the
GDT, which meant this condition was always false, but future calls to
this function that will try to edit an existing entry would fail.
Add a kernel data segment and make the user code segment come after
the data segment. We need the GDT to be in a certain order to support
the syscall and sysret instruction pair.
In order to reduce our reliance on __builtin_{ffs, clz, ctz, popcount},
this commit removes all calls to these functions and replaces them with
the equivalent functions in AK/BuiltinWrappers.h.
Unsurprisingly, the /proc/PID/stacks/TID stack walk had the same
arbitrary memory read problem as the perf event stack walk.
It would be nice if the kernel had a single stack walk implementation,
but that's outside the scope of this commit.
The platform independent Processor.h file includes the shared processor
code and includes the specific platform header file.
All references to the Arch/x86/Processor.h file have been replaced with
a reference to Arch/Processor.h.
This fixes a triple fault that occurs when compiling serenity with
the i686 clang toolchain. (The underlying issue is that the old inline
assembly did not specify that it clobbered the eax/ecx/edx registers
and as such the compiler assumed they were not changed and used their
values across it)
Co-authored-by: Brian Gianforcaro <bgianf@serenityos.org>
Initializing the variable this way fixes a kernel panic in Clang where
the object was zero-initialized, so the `m_in_scheduler` contained the
wrong value. GCC got it right, but we're better off making this change,
as leaving uninitialized fields in constant-initialized objects can
cause other weird situations like this. Also, initializing only a single
field to a non-zero value isn't worth the cost of no longer fitting in
`.bss`.
Another two variables suffer from the same problem, even though their
values are supposed to be zero. Removing these causes the
`_GLOBAL_sub_I_` function to no longer be generated and the (not
handled) `.init_array` section to be omitted.
