The following commit has been merged into the x86/urgent branch of tip: Commit-ID: 81f755d561f365f544795fad92f05a085ea4f292 Gitweb: https://git.kernel.org/tip/81f755d561f365f544795fad92f05a085ea4f292 Author: Brian Gerst <brgerst@xxxxxxxxx> AuthorDate: Fri, 23 Jun 2023 18:55:28 -04:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Mon, 10 Jul 2023 09:52:24 +02:00 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: Brian Gerst <brgerst@xxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> Link: https://lkml.kernel.org/r/20230623225529.34590-2-brgerst@xxxxxxxxx --- arch/x86/entry/entry_32.S | 33 ++++++++++----------------------- 1 file changed, 10 insertions(+), 23 deletions(-) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 91397f5..e56123f 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -720,26 +720,6 @@ 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. * * eax: prev task we switched from @@ -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
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