[tip:x86/asm] x86/entry/32: Open-code return tracking from fork and kthreads

[tip-bot for Andy Lutomirski]

Commit-ID:  39e8701f33d65c7f51d749a5d12a1379065e0926
Gitweb:     http://git.kernel.org/tip/39e8701f33d65c7f51d749a5d12a1379065e0926
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Mon, 5 Oct 2015 17:48:13 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 9 Oct 2015 09:41:10 +0200

x86/entry/32: Open-code return tracking from fork and kthreads

syscall_exit is going away, and return tracing is just a
function call now, so open-code the two non-syscall 32-bit
users.

While we're at it, update the big register layout comment.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/a6b3c472fda7cda0e368c3ccd553dea7447dfdd2.1444091585.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/entry/entry_32.S | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index a08ded4..36b6beb 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -3,7 +3,7 @@
  *
  * entry_32.S contains the system-call and low-level fault and trap handling routines.
  *
- * Stack layout in 'syscall_exit':
+ * Stack layout while running C code:
  *	ptrace needs to have all registers on the stack.
  *	If the order here is changed, it needs to be
  *	updated in fork.c:copy_process(), signal.c:do_signal(),
@@ -211,7 +211,11 @@ ENTRY(ret_from_fork)
 	popl	%eax
 	pushl	$0x0202				# Reset kernel eflags
 	popfl
-	jmp	syscall_exit
+
+	/* When we fork, we trace the syscall return in the child, too. */
+	movl    %esp, %eax
+	call    syscall_return_slowpath
+	jmp     restore_all
 END(ret_from_fork)
 
 ENTRY(ret_from_kernel_thread)
@@ -224,7 +228,15 @@ ENTRY(ret_from_kernel_thread)
 	movl	PT_EBP(%esp), %eax
 	call	*PT_EBX(%esp)
 	movl	$0, PT_EAX(%esp)
-	jmp	syscall_exit
+
+	/*
+	 * Kernel threads return to userspace as if returning from a syscall.
+	 * We should check whether anything actually uses this path and, if so,
+	 * consider switching it over to ret_from_fork.
+	 */
+	movl    %esp, %eax
+	call    syscall_return_slowpath
+	jmp     restore_all
 ENDPROC(ret_from_kernel_thread)
 
 /*
--
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