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exception & syscall handler improvements #91

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merged 8 commits into from
Nov 2, 2024
Merged

exception & syscall handler improvements #91

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41076b9
move userspace entering code into global_asm! block
Freax13 Nov 2, 2024
d97c42a
save and restore less kernel registers
Freax13 Nov 2, 2024
c05471b
initialize LSTAR only once
Freax13 Nov 2, 2024
47965fe
don't user indirection for userspace exception exit points
Freax13 Nov 2, 2024
cf76a2d
clear direction flag on syscall
Freax13 Nov 2, 2024
8f192c5
clear the direction flag in exception handlers
Freax13 Nov 2, 2024
fae4709
implement wrapper for TDG.VP.VEINFO.GET
Freax13 Nov 2, 2024
351dcba
implement #VE handler for unsupported CPUID leaves
Freax13 Nov 2, 2024
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3 changes: 3 additions & 0 deletions common/tdx-types/src/tdcall.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,9 @@ impl MdFieldId {
pub const LSTAR_WRITE: Self = Self::msr_bitmaps1(0xC000_0082, true);
pub const LSTAR_WRITE_MASK: u64 = Self::msr_bitmaps_mask(0xC000_0082);

pub const SFMASK_WRITE: Self = Self::msr_bitmaps1(0xC000_0084, true);
pub const SFMASK_WRITE_MASK: u64 = Self::msr_bitmaps_mask(0xC000_0084);

pub const TDVPS_L2_CTLS1: Self = Self::new(
81,
ElementSizeCode::SixtyFour,
Expand Down
27 changes: 17 additions & 10 deletions tee/kernel/src/exception.rs
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Expand Up @@ -8,6 +8,7 @@ use core::{
};

use crate::spin::lazy::Lazy;
use crate::user::process::syscall::cpu_state::exception_entry;
use alloc::alloc::alloc;
use log::{debug, error, trace};
use snp_types::intercept::VMEXIT_CPUID;
Expand Down Expand Up @@ -170,6 +171,7 @@ pub fn load_idt() {
extern "x86-interrupt" fn divide_error_handler(frame: InterruptStackFrame) {
unsafe {
naked_asm!(
"cld",
// Check whether the exception happened in userspace.
"test word ptr [rsp+16], 3",
"je {kernel_divide_error_handler}",
Expand All @@ -179,11 +181,11 @@ extern "x86-interrupt" fn divide_error_handler(frame: InterruptStackFrame) {
// Store the error code.
"mov byte ptr gs:[{VECTOR_OFFSET}], 0x0",
// Jump to the userspace exit point.
"jmp gs:[{HANDLER_OFFSET}]",
"jmp {exception_entry}",

kernel_divide_error_handler = sym kernel_divide_error_handler,
VECTOR_OFFSET = const offset_of!(PerCpu, vector),
HANDLER_OFFSET = const offset_of!(PerCpu, userspace_exception_exit_point),
exception_entry = sym exception_entry,
);
}
}
Expand All @@ -199,6 +201,7 @@ extern "x86-interrupt" fn page_fault_handler(
) {
unsafe {
naked_asm!(
"cld",
// Check whether the exception happened in userspace.
"test word ptr [rsp+16], 3",
"je 66f",
Expand All @@ -209,7 +212,7 @@ extern "x86-interrupt" fn page_fault_handler(
"mov byte ptr gs:[{VECTOR_OFFSET}], 0xe",
"pop qword ptr gs:[{ERROR_CODE_OFFSET}]",
// Jump to the userspace exit point.
"jmp gs:[{HANDLER_OFFSET}]",
"jmp {exception_entry}",

// Kernel code path:
"66:",
Expand Down Expand Up @@ -258,7 +261,7 @@ extern "x86-interrupt" fn page_fault_handler(
kernel_page_fault_handler = sym kernel_page_fault_handler,
VECTOR_OFFSET = const offset_of!(PerCpu, vector),
ERROR_CODE_OFFSET = const offset_of!(PerCpu, error_code),
HANDLER_OFFSET = const offset_of!(PerCpu, userspace_exception_exit_point),
exception_entry = sym exception_entry,
);
}
}
Expand Down Expand Up @@ -303,6 +306,7 @@ extern "x86-interrupt" fn general_protection_fault_handler(
) {
unsafe {
naked_asm!(
"cld",
// Check whether the exception happened in userspace.
"test word ptr [rsp+16], 3",
"je {kernel_general_protection_fault_handler}",
Expand All @@ -313,12 +317,12 @@ extern "x86-interrupt" fn general_protection_fault_handler(
"mov byte ptr gs:[{VECTOR_OFFSET}], 0xd",
"pop qword ptr gs:[{ERROR_CODE_OFFSET}]",
// Jump to the userspace exit point.
"jmp gs:[{HANDLER_OFFSET}]",
"jmp {exception_entry}",

kernel_general_protection_fault_handler = sym kernel_general_protection_fault_handler,
VECTOR_OFFSET = const offset_of!(PerCpu, vector),
ERROR_CODE_OFFSET = const offset_of!(PerCpu, error_code),
HANDLER_OFFSET = const offset_of!(PerCpu, userspace_exception_exit_point),
exception_entry = sym exception_entry,
);
}
}
Expand All @@ -338,6 +342,7 @@ extern "x86-interrupt" fn double_fault_handler(frame: InterruptStackFrame, code:
extern "x86-interrupt" fn vc_handler(frame: InterruptStackFrame, error_code: u64) {
unsafe {
naked_asm!(
"cld",
// Check whether the exception happened in userspace.
"test word ptr [rsp+16], 3",
"je {kernel_vc_handler}",
Expand All @@ -348,12 +353,12 @@ extern "x86-interrupt" fn vc_handler(frame: InterruptStackFrame, error_code: u64
"mov byte ptr gs:[{VECTOR_OFFSET}], 0x1d",
"pop qword ptr gs:[{ERROR_CODE_OFFSET}]",
// Jump to the userspace exit point.
"jmp gs:[{HANDLER_OFFSET}]",
"jmp {exception_entry}",

kernel_vc_handler = sym kernel_vc_handler,
VECTOR_OFFSET = const offset_of!(PerCpu, vector),
ERROR_CODE_OFFSET = const offset_of!(PerCpu, error_code),
HANDLER_OFFSET = const offset_of!(PerCpu, userspace_exception_exit_point),
exception_entry = sym exception_entry,
);
}
}
Expand All @@ -362,6 +367,7 @@ extern "x86-interrupt" fn vc_handler(frame: InterruptStackFrame, error_code: u64
extern "x86-interrupt" fn kernel_vc_handler(frame: InterruptStackFrame, code: u64) {
unsafe {
naked_asm!(
"cld",
"push r11",
"push r10",
"push r9",
Expand Down Expand Up @@ -464,11 +470,12 @@ extern "x86-interrupt" fn int0x80_handler(frame: InterruptStackFrame) {
// continue when userspace exits.
unsafe {
naked_asm!(
"cld",
"swapgs",
"mov byte ptr gs:[{VECTOR_OFFSET}], 0x80",
"jmp gs:[{HANDLER_OFFSET}]",
"jmp {exception_entry}",
VECTOR_OFFSET = const offset_of!(PerCpu, vector),
HANDLER_OFFSET = const offset_of!(PerCpu, userspace_exception_exit_point),
exception_entry = sym exception_entry,
);
}
}
2 changes: 0 additions & 2 deletions tee/kernel/src/per_cpu.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,6 @@ pub struct PerCpu {
pub gdt: OnceCell<GlobalDescriptorTable>,
pub int0x80_handler: Cell<u64>,
pub exit_with_sysret: Cell<bool>,
pub userspace_exception_exit_point: Cell<u64>,
pub exit: Cell<RawExit>,
pub vector: Cell<u8>,
pub error_code: Cell<u64>,
Expand All @@ -53,7 +52,6 @@ impl PerCpu {
gdt: OnceCell::new(),
int0x80_handler: Cell::new(0),
exit_with_sysret: Cell::new(false),
userspace_exception_exit_point: Cell::new(0),
exit: Cell::new(RawExit::Syscall),
vector: Cell::new(0),
error_code: Cell::new(0),
Expand Down
4 changes: 4 additions & 0 deletions tee/kernel/src/user.rs
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Original file line number Diff line number Diff line change
@@ -1,8 +1,12 @@
use process::syscall;

use crate::{memory::frame, rt::poll, supervisor::halt, time::advance_time};

pub mod process;

pub fn run() -> ! {
syscall::init();

loop {
while poll() {}

Expand Down
2 changes: 2 additions & 0 deletions tee/kernel/src/user/process/syscall.rs
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Expand Up @@ -62,6 +62,8 @@ pub mod args;
pub mod cpu_state;
pub mod traits;

pub use cpu_state::init;

impl Thread {
/// Returns true if the thread should continue to run.
pub async fn execute_syscall(self: Arc<Self>, args: SyscallArgs) {
Expand Down
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