diff --git a/09_privilege_level/README.CN.md b/09_privilege_level/README.CN.md new file mode 100644 index 00000000..80773a69 --- /dev/null +++ b/09_privilege_level/README.CN.md @@ -0,0 +1,182 @@ +# 教程 09 - 特权级别 + +## tl;dr + +- 在早期引导代码中,我们从`Hypervisor`特权级别(AArch64中的`EL2`)过渡到`Kernel` (`EL1`)特权级别。 + +## 目录 + +- [介绍](#介绍) +- [本教程的范围](#本教程的范围) +- [在入口点检查EL2](#在入口点检查EL2) +- [过渡准备](#过渡准备) +- [从未发生的异常中返回](#从未发生的异常中返回) +- [测试](#测试) +- [相比之前的变化(diff)](#相比之前的变化(diff)) + +## 介绍 + +应用级别的CPU具有所谓的`privilege levels`,它们具有不同的目的: + +| Typically used for | AArch64 | RISC-V | x86 | +| ------------- | ------------- | ------------- | ------------- | +| Userspace applications | EL0 | U/VU | Ring 3 | +| OS Kernel | EL1 | S/VS | Ring 0 | +| Hypervisor | EL2 | HS | Ring -1 | +| Low-Level Firmware | EL3 | M | | + +在AArch64中,`EL`代表`Exception Level`(异常级别)。如果您想获取有关其他体系结构的更多信息,请查看以下链接: +- [x86 privilege rings](https://en.wikipedia.org/wiki/Protection_ring). +- [RISC-V privilege modes](https://content.riscv.org/wp-content/uploads/2017/12/Tue0942-riscv-hypervisor-waterman.pdf). + +在继续之前,我强烈建议您先浏览一下[Programmer’s Guide for ARMv8-A]`的第3章`。它提供了关于该主题的简明概述。 + +[Programmer’s Guide for ARMv8-A]: http://infocenter.arm.com/help/topic/com.arm.doc.den0024a/DEN0024A_v8_architecture_PG.pdf + +## 本教程的范围 + +默认情况下,树莓派将始终在`EL2`中开始执行。由于我们正在编写一个传统的`Kernel`,我们需要过渡到更合适的`EL1`。 + +## 在入口点检查EL2 + +首先,我们需要确保我们实际上是在`EL2`中执行,然后才能调用相应的代码过渡到`EL1`。 +因此,我们在`boot.s`的顶部添加了一个新的检查,如果CPU核心不在`EL2`中,则将其停止。 + +``` +// Only proceed if the core executes in EL2. Park it otherwise. +mrs x0, CurrentEL +cmp x0, {CONST_CURRENTEL_EL2} +b.ne .L_parking_loop +``` + +接下来,在`boot.rs`中继续准备从`EL2`到`EL1`的过渡,通过调用`prepare_el2_to_el1_transition()`函数。 + +```rust +#[no_mangle] +pub unsafe extern "C" fn _start_rust(phys_boot_core_stack_end_exclusive_addr: u64) -> ! { + prepare_el2_to_el1_transition(phys_boot_core_stack_end_exclusive_addr); + + // Use `eret` to "return" to EL1. This results in execution of kernel_init() in EL1. + asm::eret() +} +``` + +## 过渡准备 + +由于`EL2`比`EL1`更具特权,它可以控制各种处理器功能,并允许或禁止`EL1`代码使用它们。 +其中一个例子是访问计时器和计数器寄存器。我们已经在[tutorial 07](../07_timestamps/)中使用了它们,所以当然我们希望保留它们。 +因此,我们在[Counter-timer Hypervisor Control register]中设置相应的标志,并将虚拟偏移量设置为零,以获取真实的物理值。 + +[Counter-timer Hypervisor Control register]: https://docs.rs/aarch64-cpu/9.0.0/src/aarch64_cpu/registers/cnthctl_el2.rs.html + +```rust +// Enable timer counter registers for EL1. +CNTHCTL_EL2.write(CNTHCTL_EL2::EL1PCEN::SET + CNTHCTL_EL2::EL1PCTEN::SET); + +// No offset for reading the counters. +CNTVOFF_EL2.set(0); +``` + +接下来,我们配置[Hypervisor Configuration Register],使`EL1`在`AArch64`模式下运行,而不是在`AArch32`模式下运行,这也是可能的。 + +[Hypervisor Configuration Register]: https://docs.rs/aarch64-cpu/9.0.0/src/aarch64_cpu/registers/hcr_el2.rs.html + +```rust +// Set EL1 execution state to AArch64. +HCR_EL2.write(HCR_EL2::RW::EL1IsAarch64); +``` + +## 从未发生的异常中返回 + +实际上,从较高的EL过渡到较低的EL只有一种方式,即通过执行[ERET]指令。 + +[ERET]: https://docs.rs/aarch64-cpu/9.0.0/src/aarch64_cpu/asm.rs.html#92-101 + +在这个指令中,它将会将[Saved Program Status Register - EL2]的内容复制到`Current Program Status Register - EL1`,并跳转到存储在[Exception Link Register - EL2]。 + +这基本上是在发生异常时所发生的相反过程。您将在即将发布的教程中了解更多相关内容。 + +[Saved Program Status Register - EL2]: https://docs.rs/aarch64-cpu/9.0.0/src/aarch64_cpu/registers/spsr_el2.rs.html +[Exception Link Register - EL2]: https://docs.rs/aarch64-cpu/9.0.0/src/aarch64_cpu/registers/elr_el2.rs.html + +```rust +// Set up a simulated exception return. +// +// First, fake a saved program status where all interrupts were masked and SP_EL1 was used as a +// stack pointer. +SPSR_EL2.write( + SPSR_EL2::D::Masked + + SPSR_EL2::A::Masked + + SPSR_EL2::I::Masked + + SPSR_EL2::F::Masked + + SPSR_EL2::M::EL1h, +); + +// Second, let the link register point to kernel_init(). +ELR_EL2.set(crate::kernel_init as *const () as u64); + +// Set up SP_EL1 (stack pointer), which will be used by EL1 once we "return" to it. Since there +// are no plans to ever return to EL2, just re-use the same stack. +SP_EL1.set(phys_boot_core_stack_end_exclusive_addr); +``` + +正如您所看到的,我们将`ELR_EL2`的值设置为之前直接从入口点调用的`kernel_init()`函数的地址。最后,我们设置了`SP_EL1`的堆栈指针。 + +您可能已经注意到,堆栈的地址作为函数参数进行了传递。正如您可能记得的,在`boot.s`的`_start()`函数中, +我们已经为`EL2`设置了堆栈。由于没有计划返回到`EL2`,我们可以直接重用相同的堆栈作为`EL1`的堆栈, +因此使用函数参数将其地址传递。 + +最后,在`_start_rust()`函数中调用了`ERET`指令。 + +```rust +#[no_mangle] +pub unsafe extern "C" fn _start_rust(phys_boot_core_stack_end_exclusive_addr: u64) -> ! { + prepare_el2_to_el1_transition(phys_boot_core_stack_end_exclusive_addr); + + // Use `eret` to "return" to EL1. This results in execution of kernel_init() in EL1. + asm::eret() +} +``` + +## 测试 + +在`main.rs`中,我们打印`current privilege level`,并额外检查`SPSR_EL2`中的掩码位是否传递到了`EL1`: + +```console +$ make chainboot +[...] +Minipush 1.0 + +[MP] ⏳ Waiting for /dev/ttyUSB0 +[MP] ✅ Serial connected +[MP] 🔌 Please power the target now + + __ __ _ _ _ _ +| \/ (_)_ _ (_) | ___ __ _ __| | +| |\/| | | ' \| | |__/ _ \/ _` / _` | +|_| |_|_|_||_|_|____\___/\__,_\__,_| + + Raspberry Pi 3 + +[ML] Requesting binary +[MP] ⏩ Pushing 14 KiB =========================================🦀 100% 0 KiB/s Time: 00:00:00 +[ML] Loaded! Executing the payload now + +[ 0.162546] mingo version 0.9.0 +[ 0.162745] Booting on: Raspberry Pi 3 +[ 0.163201] Current privilege level: EL1 +[ 0.163677] Exception handling state: +[ 0.164122] Debug: Masked +[ 0.164511] SError: Masked +[ 0.164901] IRQ: Masked +[ 0.165291] FIQ: Masked +[ 0.165681] Architectural timer resolution: 52 ns +[ 0.166255] Drivers loaded: +[ 0.166592] 1. BCM PL011 UART +[ 0.167014] 2. BCM GPIO +[ 0.167371] Timer test, spinning for 1 second +[ 1.167904] Echoing input now +``` + +## 相比之前的变化(diff) +请检查[英文版本](README.md#diff-to-previous),这是最新的。