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Adjust unsafe blocks in syscall.rs

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This commit is contained in:
Ruihan Li 2025-04-18 16:15:17 +08:00 committed by Tate, Hongliang Tian
parent c9a7d501b2
commit bf4950965b
2 changed files with 35 additions and 18 deletions
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4
ostd/src/arch/x86/trap/mod.rs
View File

@ -123,7 +123,9 @@ pub unsafe fn init() {
unsafe { gdt::init() };
idt::init();
syscall::init();
// SAFETY: `gdt::init` has been called before.
unsafe { syscall::init() };
}
/// User space context.

49
ostd/src/arch/x86/trap/syscall.rs
View File

@ -36,31 +36,46 @@ global_asm!(
USER_SS = const super::gdt::USER_SS.0,
);
pub(super) fn init() {
/// # Safety
///
/// The caller needs to ensure that `gdt::init` has been called before, so the segment selectors
/// used in the `syscall` and `sysret` instructions have been properly initialized.
pub(super) unsafe fn init() {
let cpuid = CpuId::new();
assert!(cpuid
.get_extended_processor_and_feature_identifiers()
.unwrap()
.has_syscall_sysret());
assert!(cpuid.get_extended_feature_info().unwrap().has_fsgsbase());
// Flags to clear on syscall.
//
// Linux 5.0 uses TF|DF|IF|IOPL|AC|NT. Reference:
// <https://github.com/torvalds/linux/blob/v5.0/arch/x86/kernel/cpu/common.c#L1559-L1562>
const RFLAGS_MASK: u64 = 0x47700;
// SAFETY: The segment selectors are correctly initialized (as upheld by the caller), and the
// entry point and flags to clear are also correctly set, so enabling the `syscall` and
// `sysret` instructions is safe.
unsafe {
// Enable `syscall` instruction.
assert!(cpuid
.get_extended_processor_and_feature_identifiers()
.unwrap()
.has_syscall_sysret());
LStar::write(VirtAddr::new(syscall_entry as usize as u64));
SFMask::write(RFlags::from_bits(RFLAGS_MASK).unwrap());
// Enable the `syscall` and `sysret` instructions.
Efer::update(|efer| {
efer.insert(EferFlags::SYSTEM_CALL_EXTENSIONS);
});
}
// Enable `FSGSBASE` instructions.
assert!(cpuid.get_extended_feature_info().unwrap().has_fsgsbase());
// SAFETY: Enabling the `rdfsbase`, `wrfsbase`, `rdgsbase`, and `wrgsbase` instructions is safe
// as long as the kernel properly deals with the arbitrary base values set by the userspace
// program. (FIXME: Do we really need to unconditionally enable them?)
unsafe {
Cr4::update(|cr4| {
cr4.insert(Cr4Flags::FSGSBASE);
});
// Flags to clear on syscall.
// Copy from Linux 5.0, TF|DF|IF|IOPL|AC|NT
const RFLAGS_MASK: u64 = 0x47700;
LStar::write(VirtAddr::new(syscall_entry as usize as u64));
SFMask::write(RFlags::from_bits(RFLAGS_MASK).unwrap());
}
})
};
}
extern "sysv64" {