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syscall: Properly handle a non-canonical return RIP

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This commit is contained in:
Christopher Fandrich
2026-09-22 13:11:10 -07:00
parent 0a21f7c852
commit a6fd10c211
1 changed files with 44 additions and 26 deletions
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kernel-src/arch/x86-64/syscall.asm
+44 -26
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@@ -217,6 +217,32 @@ dq syscall_eventfd
syscallcount equ 107
section .text
global arch_syscall_entry
%macro restore_context 0
add rsp, 32 ; r9 argument, cr2, gs, and fs are not popped.
pop rbx
mov es,rbx
pop rbx
mov ds,rbx
pop rax
pop rbx
pop rcx
pop rdx
pop r8
pop r9
pop r10
pop r11
pop r12
pop r13
pop r14
pop r15
pop rdi
pop rsi
add rsp, 8 ; remove irq
pop rbp
add rsp, 8 ; remove error code
%endmacro
; on entry:
; rcx has the return address
; r11 has the old rflags
@@ -292,7 +318,7 @@ arch_syscall_entry:
sti
mov rdi, rax
extern arch_syscall_log
call arch_syscall_log ; compiled with __attribute__((no_caller_saved_registers))
call arch_syscall_log ; compiled with __attribute__((no_caller_saved_registers))
; prepare context argument
mov rdi, rsp
@@ -317,7 +343,7 @@ arch_syscall_entry:
mov rdi, rax
mov rsi, rdx
extern arch_syscall_log_return
call arch_syscall_log_return ; compiled with __attribute__((no_caller_saved_registers))
call arch_syscall_log_return ; compiled with __attribute__((no_caller_saved_registers))
mov rdi, rsp
add rdi, 8 ; context pointer is after r9 argument
@@ -329,32 +355,24 @@ arch_syscall_entry:
call sched_userspacecheck ; compiled with __attribute__((no_caller_saved_registers))
cli
; restore context
add rsp, 32 ; r9 argument, cr2, gs, and fs are not popped.
pop rbx
mov es,rbx
pop rbx
mov ds,rbx
pop rax
pop rbx
pop rcx
pop rdx
pop r8
pop r9
pop r10
pop r11
pop r12
pop r13
pop r14
pop r15
pop rdi
pop rsi
add rsp, 8 ; remove irq
pop rbp
add rsp, 8 ; remove error code
; on intel cpu's, a non-canonical rip will cause a #GP in ring 0 on the user stack when sysret is used
mov rax, [rdi + 176] ; context->rip
mov rbx, rax
shl rax, 64 - 48 ; this breaks if LA57 is enabled (it's not)
sar rax, 64 - 48
cmp rax, rbx
jne .gpf
restore_context
pop rcx
add rsp, 8 ; user CS
pop r11 ; rflags
pop r11 ; rflags
pop rsp
swapgs
o64 sysret
.gpf:
restore_context
push 0 ; error code
swapgs
extern isr_table
jmp [isr_table + 13 * 8] ; jump to the #GP handler with the user interrupt frame