linux-kernel - [RFC/PATCH v2 v2 4/6] x86/entry/32: Remove unnecessary asm check for returns to kernel mode

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Date:	Thu,  9 Jul 2015 19:17:32 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Borislav Petkov <bp@...en8.de>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: [RFC/PATCH v2 v2 4/6] x86/entry/32: Remove unnecessary asm check for returns to kernel mode

Unless I missed something, 44fbbb3dc687c ("x86: get rid of calling
do_notify_resume() when returning to kernel mode") was unnecessarily
paranoid.  It split the exit path into resume_userspace and
resume_kernel, after which it was no longer possible to get to
work_notifysig when returning to kernel mode.  The check for kernel
mode in work_notifysig is superfluous.  Remove it.

Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/entry_32.S | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index a36d5df6a749..66ff9c4055d7 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -491,10 +491,6 @@ work_notifysig:					# deal with pending signals and
 #endif
 	TRACE_IRQS_ON
 	ENABLE_INTERRUPTS(CLBR_NONE)
-	movb	PT_CS(%esp), %bl
-	andb	$SEGMENT_RPL_MASK, %bl
-	cmpb	$USER_RPL, %bl
-	jb	resume_kernel
 	xorl	%edx, %edx
 	call	do_notify_resume
 	jmp	resume_userspace
-- 
2.4.3

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