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Kernel: Implement and use the syscall/sysret instruction pair on x86_64

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Owen Smith 2021-07-23 21:52:25 +01:00 • committed by Andreas Kling
parent d36c84c331
commit e6df1c9988
6 changed files with 169 additions and 1 deletions
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23
Kernel/Arch/x86/common/Processor.cpp
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@ -45,6 +45,7 @@ Atomic<u32> Processor::s_idle_cpu_mask { 0 };
extern "C" void context_first_init(Thread* from_thread, Thread* to_thread, TrapFrame* trap) __attribute__((used));
extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread) __attribute__((used));
extern "C" FlatPtr do_init_context(Thread* thread, u32 flags) __attribute__((used));
extern "C" void syscall_entry();
bool Processor::is_smp_enabled()
{
@ -220,6 +221,28 @@ UNMAP_AFTER_INIT void Processor::cpu_setup()
write_xcr0(read_xcr0() | 0x7);
}
}
#if ARCH(X86_64)
// x86_64 processors must have the syscall feature.
VERIFY(has_feature(CPUFeature::SYSCALL));
MSR efer_msr(MSR_EFER);
efer_msr.set(efer_msr.get() | 1u);
// Write code and stack selectors to the STAR MSR. The first value stored in bits 63:48 controls the sysret CS (value + 0x10) and SS (value + 0x8),
// and the value stored in bits 47:32 controls the syscall CS (value) and SS (value + 0x8).
u64 star = 0;
star |= 0x13ul << 48u;
star |= 0x08ul << 32u;
MSR star_msr(MSR_STAR);
star_msr.set(star);
// Write the syscall entry point to the LSTAR MSR, and write the SFMASK MSR to clear rflags upon entry.
// The userspace rflags will be preserved in r11.
MSR lstar_msr(MSR_LSTAR);
MSR sfmask_msr(MSR_SFMASK);
lstar_msr.set(reinterpret_cast<u64>(&syscall_entry));
sfmask_msr.set(~0x2);
#endif
}
String Processor::features_string() const