Commit 81f755d5 authored by Brian Gerst's avatar Brian Gerst Committed by Peter Zijlstra
Browse files

x86/32: Remove schedule_tail_wrapper() 



The unwinder expects a return address at the very top of the kernel
stack just below pt_regs and before any stack frame is created.  Instead
of calling a wrapper, set up a return address as if ret_from_fork()
was called from the syscall entry code.

Signed-off-by: default avatarBrian Gerst <brgerst@gmail.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarSami Tolvanen <samitolvanen@google.com>
Link: https://lkml.kernel.org/r/20230623225529.34590-2-brgerst@gmail.com
parent 9831c625

arch/x86/entry/entry_32.S

+10 −23
Original line number Diff line number Diff line
@@ -719,26 +719,6 @@ SYM_CODE_START(__switch_to_asm) 
SYM_CODE_END(__switch_to_asm)

.popsection



/*

 * The unwinder expects the last frame on the stack to always be at the same

 * offset from the end of the page, which allows it to validate the stack.

 * Calling schedule_tail() directly would break that convention because its an

 * asmlinkage function so its argument has to be pushed on the stack.  This

 * wrapper creates a proper "end of stack" frame header before the call.

 */

.pushsection .text, "ax"

SYM_FUNC_START(schedule_tail_wrapper)

	FRAME_BEGIN



	pushl	%eax

	call	schedule_tail

	popl	%eax



	FRAME_END

	RET

SYM_FUNC_END(schedule_tail_wrapper)

.popsection



/*

 * A newly forked process directly context switches into this address.

 *
@@ -748,16 +728,23 @@ SYM_FUNC_END(schedule_tail_wrapper) 
 */

.pushsection .text, "ax"

SYM_CODE_START(ret_from_fork)

	call	schedule_tail_wrapper

	/* return address for the stack unwinder */

	pushl	$.Lsyscall_32_done



	FRAME_BEGIN

	pushl	%eax

	call	schedule_tail

	addl	$4, %esp

	FRAME_END



	testl	%ebx, %ebx

	jnz	1f		/* kernel threads are uncommon */



2:

	/* When we fork, we trace the syscall return in the child, too. */

	movl    %esp, %eax

	leal    4(%esp), %eax

	call    syscall_exit_to_user_mode

	jmp     .Lsyscall_32_done

	RET



	/* kernel thread */

1:	movl	%edi, %eax