diff options
Diffstat (limited to 'arch/x86/entry/entry_64.S')
| -rw-r--r-- | arch/x86/entry/entry_64.S | 43 |
1 files changed, 20 insertions, 23 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index f31e286c2977..43606de22511 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -284,36 +284,33 @@ SYM_FUNC_END(__switch_to_asm) * r12: kernel thread arg */ .pushsection .text, "ax" - __FUNC_ALIGN -SYM_CODE_START_NOALIGN(ret_from_fork) +SYM_CODE_START(ret_from_fork_asm) + /* + * This is the start of the kernel stack; even through there's a + * register set at the top, the regset isn't necessarily coherent + * (consider kthreads) and one cannot unwind further. + * + * This ensures stack unwinds of kernel threads terminate in a known + * good state. + */ UNWIND_HINT_END_OF_STACK ANNOTATE_NOENDBR // copy_thread CALL_DEPTH_ACCOUNT - movq %rax, %rdi - call schedule_tail /* rdi: 'prev' task parameter */ - testq %rbx, %rbx /* from kernel_thread? */ - jnz 1f /* kernel threads are uncommon */ + movq %rax, %rdi /* prev */ + movq %rsp, %rsi /* regs */ + movq %rbx, %rdx /* fn */ + movq %r12, %rcx /* fn_arg */ + call ret_from_fork -2: - UNWIND_HINT_REGS - movq %rsp, %rdi - call syscall_exit_to_user_mode /* returns with IRQs disabled */ - jmp swapgs_restore_regs_and_return_to_usermode - -1: - /* kernel thread */ - UNWIND_HINT_END_OF_STACK - movq %r12, %rdi - CALL_NOSPEC rbx /* - * A kernel thread is allowed to return here after successfully - * calling kernel_execve(). Exit to userspace to complete the execve() - * syscall. + * Set the stack state to what is expected for the target function + * -- at this point the register set should be a valid user set + * and unwind should work normally. */ - movq $0, RAX(%rsp) - jmp 2b -SYM_CODE_END(ret_from_fork) + UNWIND_HINT_REGS + jmp swapgs_restore_regs_and_return_to_usermode +SYM_CODE_END(ret_from_fork_asm) .popsection .macro DEBUG_ENTRY_ASSERT_IRQS_OFF |