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x86/32: Remove schedule_tail_wrapper()

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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: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lkml.kernel.org/r/20230623225529.34590-2-brgerst@gmail.com
This commit is contained in:
Brian Gerst 2023-06-23 18:55:28 -04:00 committed by Peter Zijlstra
parent 9831c6253a
commit 81f755d561
1 changed files with 10 additions and 23 deletions
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33
arch/x86/entry/entry_32.S
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@ -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