6b20f1fb19
QEMU handles bits bring written in the (reserved) high bits of SFMASK just fine, but KVM gives a #GP exception.
125 lines
2.3 KiB
ArmAsm
125 lines
2.3 KiB
ArmAsm
%include "tasking.inc"
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%include "syscalls.inc"
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; SYSCALL/SYSRET control MSRs
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MSR_STAR equ 0xc0000081
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MSR_LSTAR equ 0xc0000082
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MSR_FMASK equ 0xc0000084
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; IA32_STAR - high 32 bits contain k+u CS
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; Kernel CS: GDT[1] ring 0 bits[47:32]
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; User CS: GDT[3] ring 3 bits[63:48]
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STAR_HIGH equ \
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(((1 << 3) | 0)) | \
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(((3 << 3) | 3) << 16)
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; IA32_FMASK - Mask off interrupts in syscalls
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FMASK_VAL equ 0x200
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extern __counter_syscall_enter
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extern __counter_syscall_sysret
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extern syscall_registry
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extern syscall_invalid
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global syscall_handler_prelude:function (syscall_handler_prelude.end - syscall_handler_prelude)
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syscall_handler_prelude:
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push rbp ; Never executed, fake function prelude
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mov rbp, rsp ; to calm down gdb
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.real:
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swapgs
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mov [gs:CPU_DATA.rsp3], rsp
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mov rsp, [gs:CPU_DATA.rsp0]
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mov [gs:CPU_DATA.rflags3], r11
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push rcx
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push rbp
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mov rbp, rsp
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; account for the hole in the sysv abi
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; argument list since SYSCALL uses rcx.
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; r10 is non-preserved but not part of
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; the function call ABI, so the rcx arg
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; was stashed there.
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mov rcx, r10
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push rbx
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push r12
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push r13
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push r14
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push r15
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; if we've got more than 6 arguments, the rest
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; are on the user stack, and pointed to by rbx.
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; push rbx so that it's the 7th argument.
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push rbx
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inc qword [rel __counter_syscall_enter]
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cmp rax, NUM_SYSCALLS
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jge .bad_syscall
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lea r11, [rel syscall_registry]
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mov r11, [r11 + rax * 8]
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cmp r11, 0
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je .bad_syscall
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call r11
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add rsp, 8 ; account for passing rbx on the stack
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inc qword [rel __counter_syscall_sysret]
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jmp kernel_to_user_trampoline
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.bad_syscall:
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mov rdi, rax
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call syscall_invalid
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.end:
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global kernel_to_user_trampoline:function (kernel_to_user_trampoline.end - kernel_to_user_trampoline)
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kernel_to_user_trampoline:
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pop r15
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pop r14
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pop r13
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pop r12
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pop rbx
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pop rbp
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pop rcx
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mov r11, [gs:CPU_DATA.tss]
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mov [r11 + TSS.rsp0], rsp
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mov [gs:CPU_DATA.rsp0], rsp
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mov rsp, [gs:CPU_DATA.rsp3]
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mov r11, [gs:CPU_DATA.rflags3]
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swapgs
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o64 sysret
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.end:
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global syscall_enable:function (syscall_enable.end - syscall_enable)
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syscall_enable:
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push rbp
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mov rbp, rsp
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mov rcx, MSR_STAR
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mov rax, 0
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mov rdx, STAR_HIGH
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wrmsr
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mov rcx, MSR_LSTAR
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mov rax, syscall_handler_prelude.real
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mov rdx, rax
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shr rdx, 32
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wrmsr
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mov rcx, MSR_FMASK
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mov rax, FMASK_VAL
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mov rdx, 0
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wrmsr
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pop rbp
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ret
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.end:
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