From fb57db26d0b9472d4c93ae45fd7f6c17c0d632ad Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 20 Sep 2022 17:59:59 +0800
Subject: [PATCH] x86/retpoline: Use -mfunction-return

stable inclusion
from stable-v5.10.133
commit 270de63cf4a380fe9942d3e0da599c0e966fad78
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5PTAS
CVE: CVE-2022-29900,CVE-2022-23816,CVE-2022-29901

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=270de63cf4a380fe9942d3e0da599c0e966fad78

--------------------------------

commit 0b53c374b9eff2255a386f1f1cfb9a928e52a5ae upstream.

Utilize -mfunction-return=thunk-extern when available to have the
compiler replace RET instructions with direct JMPs to the symbol
__x86_return_thunk. This does not affect assembler (.S) sources, only C
sources.

-mfunction-return=thunk-extern has been available since gcc 7.3 and
clang 15.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
[cascardo: RETPOLINE_CFLAGS is at Makefile]
[cascardo: remove ANNOTATE_NOENDBR from __x86_return_thunk]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lin Yujun <linyujun809@huawei.com>
Reviewed-by: Zhang Jianhua <chris.zjh@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
---
 Makefile                             |  2 ++
 arch/x86/include/asm/nospec-branch.h |  2 ++
 arch/x86/lib/retpoline.S             | 12 ++++++++++++
 3 files changed, 16 insertions(+)

diff --git a/Makefile b/Makefile
index ebb503a59db2..963734589fe6 100644
--- a/Makefile
+++ b/Makefile
@@ -672,11 +672,13 @@ endif
 
 ifdef CONFIG_CC_IS_GCC
 RETPOLINE_CFLAGS	:= $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
+RETPOLINE_CFLAGS	+= $(call cc-option,-mfunction-return=thunk-extern)
 RETPOLINE_VDSO_CFLAGS	:= $(call cc-option,-mindirect-branch=thunk-inline -mindirect-branch-register)
 endif
 ifdef CONFIG_CC_IS_CLANG
 RETPOLINE_CFLAGS	:= -mretpoline-external-thunk
 RETPOLINE_VDSO_CFLAGS	:= -mretpoline
+RETPOLINE_CFLAGS	+= $(call cc-option,-mfunction-return=thunk-extern)
 endif
 export RETPOLINE_CFLAGS
 export RETPOLINE_VDSO_CFLAGS
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index e791fe7e9de5..6eedd835613c 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -120,6 +120,8 @@
 	_ASM_PTR " 999b\n\t"					\
 	".popsection\n\t"
 
+extern void __x86_return_thunk(void);
+
 #ifdef CONFIG_RETPOLINE
 
 typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE];
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index c013241d9188..01667ea9da02 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -66,3 +66,15 @@ SYM_CODE_END(__x86_indirect_thunk_array)
 #define GEN(reg) EXPORT_THUNK(reg)
 #include <asm/GEN-for-each-reg.h>
 #undef GEN
+
+/*
+ * This function name is magical and is used by -mfunction-return=thunk-extern
+ * for the compiler to generate JMPs to it.
+ */
+SYM_CODE_START(__x86_return_thunk)
+	UNWIND_HINT_EMPTY
+	ret
+	int3
+SYM_CODE_END(__x86_return_thunk)
+
+__EXPORT_THUNK(__x86_return_thunk)
-- 
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