x86/asm: Fixup odd GEN-for-each-reg.h usage

stable inclusion
from stable-v5.10.133
commit 41ef958070000770758531247db417523aa6977f
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=41ef958070000770758531247db417523aa6977f

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

commit b6d3d994 upstream.

Currently GEN-for-each-reg.h usage leaves GEN defined, relying on any
subsequent usage to start with #undef, which is rude.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NBorislav Petkov <bp@suse.de>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Tested-by: NAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20211026120310.041792350@infradead.orgSigned-off-by: NThadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: NBen Hutchings <ben@decadent.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NLin Yujun <linyujun809@huawei.com>
Reviewed-by: NZhang Jianhua <chris.zjh@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/x86/include/asm/asm-prototypes.h

@@ -19,9 +19,9 @@ extern void cmpxchg8b_emu(void);
 
 #ifdef CONFIG_RETPOLINE
 
-#undef GEN
 #define GEN(reg) \
 	extern asmlinkage void __x86_indirect_thunk_ ## reg (void);
 #include <asm/GEN-for-each-reg.h>
+#undef GEN
 
 #endif /* CONFIG_RETPOLINE */

arch/x86/lib/retpoline.S

@@ -55,10 +55,10 @@ SYM_FUNC_END(__x86_indirect_thunk_\reg)
 #define __EXPORT_THUNK(sym)	_ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym)
 #define EXPORT_THUNK(reg)	__EXPORT_THUNK(__x86_indirect_thunk_ ## reg)
 
-#undef GEN
 #define GEN(reg) THUNK reg
 #include <asm/GEN-for-each-reg.h>
-
 #undef GEN
+
 #define GEN(reg) EXPORT_THUNK(reg)
 #include <asm/GEN-for-each-reg.h>
+#undef GEN