linux-kernel - [PATCH V2 8/9] x86/speculation: Add unwind hint to trampoline return

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Message-Id: <20200407073142.20659-9-alexandre.chartre@oracle.com>
Date:   Tue,  7 Apr 2020 09:31:41 +0200
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, jpoimboe@...hat.com,
        peterz@...radead.org, jthierry@...hat.com, tglx@...utronix.de,
        alexandre.chartre@...cle.com
Subject: [PATCH V2 8/9] x86/speculation: Add unwind hint to trampoline return

With retpoline, the address to branch to is pushed on the stack and
the return instruction (ret) is used to jump to that address. Use the
UNWIND_HINT_RET_OFFSET directive to inform objtool that the stack
should be adjusted.

Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>

replace RETPOLINE_RET with UNWIND_HINT_RET_OFFSET
---
 arch/x86/include/asm/nospec-branch.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index a345c6fa0541..5ce2a40a26da 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -10,6 +10,7 @@
 #include <asm/alternative-asm.h>
 #include <asm/cpufeatures.h>
 #include <asm/msr-index.h>
+#include <asm/unwind_hints.h>
 
 /*
  * This should be used immediately before a retpoline alternative. It tells
@@ -100,6 +101,7 @@
 	jmp	.Lspec_trap_\@
 .Ldo_rop_\@:
 	mov	\reg, (%_ASM_SP)
+	UNWIND_HINT_RET_OFFSET
 	ret
 .endm
 
-- 
2.18.2