x86: Prepare inline-asm for straight-line-speculation

Replace all ret/retq instructions with ASM_RET in preparation of
making it more than a single instruction.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211204134907.964635458@infradead.org

arch/x86/include/asm/linkage.h

@@ -18,6 +18,10 @@
 #define __ALIGN_STR	__stringify(__ALIGN)
 #endif
 
+#else /* __ASSEMBLY__ */
+
+#define ASM_RET	"ret\n\t"
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_LINKAGE_H */

arch/x86/include/asm/paravirt.h

@@ -671,7 +671,7 @@ bool __raw_callee_save___native_vcpu_is_preempted(long cpu);
 	    "call " #func ";"						\
 	    PV_RESTORE_ALL_CALLER_REGS					\
 	    FRAME_END							\
-	    "ret;"							\
+	    ASM_RET							\
 	    ".size " PV_THUNK_NAME(func) ", .-" PV_THUNK_NAME(func) ";"	\
 	    ".popsection")
 

arch/x86/include/asm/qspinlock_paravirt.h

@@ -48,7 +48,7 @@ asm    (".pushsection .text;"
 	"jne   .slowpath;"
 	"pop   %rdx;"
 	FRAME_END
-	"ret;"
+	ASM_RET
 	".slowpath: "
 	"push   %rsi;"
 	"movzbl %al,%esi;"
@@ -56,7 +56,7 @@ asm    (".pushsection .text;"
 	"pop    %rsi;"
 	"pop    %rdx;"
 	FRAME_END
-	"ret;"
+	ASM_RET
 	".size " PV_UNLOCK ", .-" PV_UNLOCK ";"
 	".popsection");
 

arch/x86/kernel/alternative.c

@@ -714,7 +714,7 @@ asm (
 "	.type		int3_magic, @function\n"
 "int3_magic:\n"
 "	movl	$1, (%" _ASM_ARG1 ")\n"
-"	ret\n"
+	ASM_RET
 "	.size		int3_magic, .-int3_magic\n"
 "	.popsection\n"
 );

arch/x86/kernel/kprobes/core.c

@@ -1051,7 +1051,7 @@ asm(
 	"	addl $4, %esp\n"
 	"	popfl\n"
 #endif
-	"	ret\n"
+	ASM_RET
 	".size __kretprobe_trampoline, .-__kretprobe_trampoline\n"
 );
 NOKPROBE_SYMBOL(__kretprobe_trampoline);

arch/x86/kernel/paravirt.c

@@ -41,7 +41,7 @@ extern void _paravirt_nop(void);
 asm (".pushsection .entry.text, \"ax\"\n"
      ".global _paravirt_nop\n"
      "_paravirt_nop:\n\t"
-     "ret\n\t"
+     ASM_RET
      ".size _paravirt_nop, . - _paravirt_nop\n\t"
      ".type _paravirt_nop, @function\n\t"
      ".popsection");
@@ -51,7 +51,7 @@ asm (".pushsection .entry.text, \"ax\"\n"
      ".global paravirt_ret0\n"
      "paravirt_ret0:\n\t"
      "xor %" _ASM_AX ", %" _ASM_AX ";\n\t"
-     "ret\n\t"
+     ASM_RET
      ".size paravirt_ret0, . - paravirt_ret0\n\t"
      ".type paravirt_ret0, @function\n\t"
      ".popsection");

arch/x86/kvm/emulate.c

@@ -315,7 +315,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
 	__FOP_FUNC(#name)
 
 #define __FOP_RET(name) \
-	"ret \n\t" \
+	ASM_RET \
 	".size " name ", .-" name "\n\t"
 
 #define FOP_RET(name) \
@@ -435,7 +435,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
 	__FOP_RET(#op)
 
 asm(".pushsection .fixup, \"ax\"\n"
-    "kvm_fastop_exception: xor %esi, %esi; ret\n"
+    "kvm_fastop_exception: xor %esi, %esi; " ASM_RET
     ".popsection");
 
 FOP_START(setcc)

arch/x86/lib/error-inject.c

 // SPDX-License-Identifier: GPL-2.0
 
+#include <linux/linkage.h>
 #include <linux/error-injection.h>
 #include <linux/kprobes.h>
 
@@ -10,7 +11,7 @@ asm(
 	".type just_return_func, @function\n"
 	".globl just_return_func\n"
 	"just_return_func:\n"
-	"	ret\n"
+		ASM_RET
 	".size just_return_func, .-just_return_func\n"
 );
 

samples/ftrace/ftrace-direct-modify.c

@@ -31,7 +31,7 @@ asm (
 "	call my_direct_func1\n"
 "	leave\n"
 "	.size		my_tramp1, .-my_tramp1\n"
-"	ret\n"
+	ASM_RET
 "	.type		my_tramp2, @function\n"
 "	.globl		my_tramp2\n"
 "   my_tramp2:"
@@ -39,7 +39,7 @@ asm (
 "	movq %rsp, %rbp\n"
 "	call my_direct_func2\n"
 "	leave\n"
-"	ret\n"
+	ASM_RET
 "	.size		my_tramp2, .-my_tramp2\n"
 "	.popsection\n"
 );

samples/ftrace/ftrace-direct-too.c

@@ -31,7 +31,7 @@ asm (
 "	popq %rsi\n"
 "	popq %rdi\n"
 "	leave\n"
-"	ret\n"
+	ASM_RET
 "	.size		my_tramp, .-my_tramp\n"
 "	.popsection\n"
 );

samples/ftrace/ftrace-direct.c

@@ -25,7 +25,7 @@ asm (
 "	call my_direct_func\n"
 "	popq %rdi\n"
 "	leave\n"
-"	ret\n"
+	ASM_RET
 "	.size		my_tramp, .-my_tramp\n"
 "	.popsection\n"
 );