From: Andi Kleen <andi@firstfloor.org>
To: tglx@linutronix.de
Cc: torvalds@linux-foundation.org, gregkh@linux-foundation.org,
linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com,
Andi Kleen <ak@linux.intel.com>,
jpoimboe@redhat.com
Subject: [PATCH v2 12/12] retpoline: Attempt to quiten objtool warning for unreachable code
Date: Wed, 3 Jan 2018 18:00:19 -0800 [thread overview]
Message-ID: <20180104020019.1173-13-andi@firstfloor.org> (raw)
In-Reply-To: <20180104020019.1173-1-andi@firstfloor.org>
From: Andi Kleen <ak@linux.intel.com>
The speculative jump trampoline has to contain unreachable code.
objtool keeps complaining
arch/x86/lib/retpoline.o: warning: objtool: __x86.indirect_thunk()+0x8: unreachable instruction
I tried to fix it here by adding ASM_UNREACHABLE annotation (after
supporting them for pure assembler), but it still complains.
Seems like a objtool bug?
So it doesn't actually fix the warning oyet.
Of course it's just a warning so the kernel will still work fine.
Perhaps Josh can figure it out
Cc: jpoimboe@redhat.com
Not-Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
arch/x86/lib/retpoline.S | 3 +++
include/linux/compiler.h | 10 +++++++++-
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index cb40781adbfe..f4ed556a90ee 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -11,6 +11,7 @@
*/
#include <linux/linkage.h>
+#include <linux/compiler.h>
#include <asm/dwarf2.h>
#include <asm/export.h>
@@ -21,7 +22,9 @@ ENTRY(__x86.indirect_thunk)
call retpoline_call_target
2:
lfence /* stop speculation */
+ ASM_UNREACHABLE
jmp 2b
+ ASM_UNREACHABLE
retpoline_call_target:
#ifdef CONFIG_64BIT
lea 8(%rsp), %rsp
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 52e611ab9a6c..cfba91acc79a 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -269,7 +269,15 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
#endif /* __KERNEL__ */
-#endif /* __ASSEMBLY__ */
+#else /* __ASSEMBLY__ */
+
+#define ASM_UNREACHABLE \
+ 999: \
+ .pushsection .discard.unreachable; \
+ .long 999b - .; \
+ .popsection
+
+#endif /* !__ASSEMBLY__ */
/* Compile time object size, -1 for unknown */
#ifndef __compiletime_object_size
--
2.14.3
next prev parent reply other threads:[~2018-01-04 2:00 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-04 2:00 Avoid speculative indirect calls in kernel Andi Kleen
2018-01-04 2:00 ` [PATCH v2 01/12] x86/retpoline: Define retpoline indirect thunk and macros Andi Kleen
2018-01-04 2:15 ` Brian Gerst
2018-01-04 2:32 ` Alan Cox
2018-01-04 2:00 ` [PATCH v2 02/12] x86/retpoline/crypto: Convert crypto assembler indirect jumps Andi Kleen
2018-01-04 2:00 ` [PATCH v2 03/12] x86/retpoline/entry: Convert entry " Andi Kleen
2018-01-04 8:42 ` David Woodhouse
2018-01-04 2:00 ` [PATCH v2 04/12] x86/retpoline/ftrace: Convert ftrace " Andi Kleen
2018-01-04 2:00 ` [PATCH v2 05/12] x86/retpoline/hyperv: Convert " Andi Kleen
2018-01-04 2:00 ` [PATCH v2 06/12] x86/retpoline/crypto: Convert xen " Andi Kleen
2018-01-04 6:48 ` Juergen Gross
2018-01-04 6:50 ` Andi Kleen
2018-01-04 2:00 ` [PATCH v2 07/12] x86/retpoline/checksum32: Convert " Andi Kleen
2018-01-04 2:00 ` [PATCH v2 08/12] x86/retpoline/irq32: " Andi Kleen
2018-01-04 2:00 ` [PATCH v2 09/12] x86/retpoline: Finally enable retpoline for C code Andi Kleen
2018-01-04 2:00 ` [PATCH v2 10/12] retpoline/taint: Taint kernel for missing retpoline in compiler Andi Kleen
2018-01-04 2:00 ` [PATCH v2 11/12] retpoline/objtool: Disable some objtool warnings Andi Kleen
2018-01-04 14:38 ` Josh Poimboeuf
2018-01-04 14:46 ` David Woodhouse
2018-01-04 15:59 ` Andi Kleen
2018-01-04 16:06 ` Josh Poimboeuf
2018-01-04 16:13 ` Andi Kleen
2018-01-04 16:32 ` Josh Poimboeuf
2018-01-04 17:35 ` Josh Poimboeuf
2018-01-04 2:00 ` Andi Kleen [this message]
2018-01-04 11:49 ` Avoid speculative indirect calls in kernel Pavel Machek
2018-01-04 12:09 ` Alan Cox
2018-01-04 13:32 ` Pavel Machek
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