linux-kernel - [PATCH v14 12/24] x86/reboot: Add ljmp instructions to stacktool whitelist

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Message-Id: <90a8f2e2111c7b67f547511b9dea16914a79c964.1445443144.git.jpoimboe@redhat.com>
Date:	Wed, 21 Oct 2015 11:11:51 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
	Chris J Arges <chris.j.arges@...onical.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH v14 12/24] x86/reboot: Add ljmp instructions to stacktool whitelist

stacktool reports a false positive warning for the ljmp instruction in
machine_real_restart().  Normally, ljmp isn't allowed in a function, but
this is a special case where it's jumping into real mode.

Add the jumps to a whitelist which tells stacktool to ignore them.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/reboot.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 02693dd..1ea1c5e 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -9,6 +9,7 @@
 #include <linux/sched.h>
 #include <linux/tboot.h>
 #include <linux/delay.h>
+#include <linux/stacktool.h>
 #include <acpi/reboot.h>
 #include <asm/io.h>
 #include <asm/apic.h>
@@ -97,11 +98,13 @@ void __noreturn machine_real_restart(unsigned int type)
 
 	/* Jump to the identity-mapped low memory code */
 #ifdef CONFIG_X86_32
-	asm volatile("jmpl *%0" : :
+	asm volatile(STACKTOOL_IGNORE_INSN
+		     "jmpl *%0;" : :
 		     "rm" (real_mode_header->machine_real_restart_asm),
 		     "a" (type));
 #else
-	asm volatile("ljmpl *%0" : :
+	asm volatile(STACKTOOL_IGNORE_INSN
+		     "ljmpl *%0" : :
 		     "m" (real_mode_header->machine_real_restart_asm),
 		     "D" (type));
 #endif
-- 
2.4.3

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