s390: extend expoline to BC instructions

The BPF JIT uses a 'b <disp>(%r<x>)' instruction in the definition
of the sk_load_word and sk_load_half functions.

Add support for branch-on-condition instructions contained in the
thunk code of an expoline.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/nospec-insn.h

@@ -35,10 +35,18 @@ _LC_BR_R1 = __LC_BR_R1
 	__THUNK_PROLOG_NAME __s390x_indirect_jump_r\r2\()use_r\r1
 	.endm
 
+	.macro __THUNK_PROLOG_BC d0,r1,r2
+	__THUNK_PROLOG_NAME __s390x_indirect_branch_\d0\()_\r2\()use_\r1
+	.endm
+
 	.macro __THUNK_BR r1,r2
 	jg	__s390x_indirect_jump_r\r2\()use_r\r1
 	.endm
 
+	.macro __THUNK_BC d0,r1,r2
+	jg	__s390x_indirect_branch_\d0\()_\r2\()use_\r1
+	.endm
+
 	.macro __THUNK_BRASL r1,r2,r3
 	brasl	\r1,__s390x_indirect_jump_r\r3\()use_r\r2
 	.endm
@@ -81,6 +89,23 @@ _LC_BR_R1 = __LC_BR_R1
 	.endif
 	.endm
 
+	.macro	__DECODE_DRR expand,disp,reg,ruse
+	.set __decode_fail,1
+	.irp r1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
+	.ifc \reg,%r\r1
+	.irp r2,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
+	.ifc \ruse,%r\r2
+	\expand \disp,\r1,\r2
+	.set __decode_fail,0
+	.endif
+	.endr
+	.endif
+	.endr
+	.if __decode_fail == 1
+	.error "__DECODE_DRR failed"
+	.endif
+	.endm
+
 	.macro __THUNK_EX_BR reg,ruse
 	# Be very careful when adding instructions to this macro!
 	# The ALTERNATIVE replacement code has a .+10 which targets
@@ -101,17 +126,42 @@ _LC_BR_R1 = __LC_BR_R1
 555:	br	\reg
 	.endm
 
+	.macro __THUNK_EX_BC disp,reg,ruse
+#ifdef CONFIG_HAVE_MARCH_Z10_FEATURES
+	exrl	0,556f
+	j	.
+#else
+	larl	\ruse,556f
+	ex	0,0(\ruse)
+	j	.
+#endif
+556:	b	\disp(\reg)
+	.endm
+
 	.macro GEN_BR_THUNK reg,ruse=%r1
 	__DECODE_RR __THUNK_PROLOG_BR,\reg,\ruse
 	__THUNK_EX_BR \reg,\ruse
 	__THUNK_EPILOG
 	.endm
 
+	.macro GEN_B_THUNK disp,reg,ruse=%r1
+	__DECODE_DRR __THUNK_PROLOG_BC,\disp,\reg,\ruse
+	__THUNK_EX_BC \disp,\reg,\ruse
+	__THUNK_EPILOG
+	.endm
+
 	.macro BR_EX reg,ruse=%r1
 557:	__DECODE_RR __THUNK_BR,\reg,\ruse
 	.pushsection .s390_indirect_branches,"a",@progbits
 	.long	557b-.
 	.popsection
+	.endm
+
+	 .macro B_EX disp,reg,ruse=%r1
+558:	__DECODE_DRR __THUNK_BC,\disp,\reg,\ruse
+	.pushsection .s390_indirect_branches,"a",@progbits
+	.long	558b-.
+	.popsection
 	.endm
 
 	.macro BASR_EX rsave,rtarget,ruse=%r1
@@ -123,10 +173,17 @@ _LC_BR_R1 = __LC_BR_R1
 
 #else
 	.macro GEN_BR_THUNK reg,ruse=%r1
+	.endm
+
+	.macro GEN_B_THUNK disp,reg,ruse=%r1
 	.endm
 
 	 .macro BR_EX reg,ruse=%r1
 	br	\reg
+	.endm
+
+	 .macro B_EX disp,reg,ruse=%r1
+	b	\disp(\reg)
 	.endm
 
 	.macro BASR_EX rsave,rtarget,ruse=%r1

arch/s390/kernel/nospec-branch.c

@@ -93,7 +93,6 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
 	s32 *epo;
 
 	/* Second part of the instruction replace is always a nop */
-	memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4);
 	for (epo = start; epo < end; epo++) {
 		instr = (u8 *) epo + *epo;
 		if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
@@ -114,18 +113,34 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
 			br = thunk + (*(int *)(thunk + 2)) * 2;
 		else
 			continue;
-		if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
+		/* Check for unconditional branch 0x07f? or 0x47f???? */
+		if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
 			continue;
+
+		memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
 		switch (type) {
 		case BRCL_EXPOLINE:
-			/* brcl to thunk, replace with br + nop */
 			insnbuf[0] = br[0];
 			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
+			if (br[0] == 0x47) {
+				/* brcl to b, replace with bc + nopr */
+				insnbuf[2] = br[2];
+				insnbuf[3] = br[3];
+			} else {
+				/* brcl to br, replace with bcr + nop */
+			}
 			break;
 		case BRASL_EXPOLINE:
-			/* brasl to thunk, replace with basr + nop */
-			insnbuf[0] = 0x0d;
 			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
+			if (br[0] == 0x47) {
+				/* brasl to b, replace with bas + nopr */
+				insnbuf[0] = 0x4d;
+				insnbuf[2] = br[2];
+				insnbuf[3] = br[3];
+			} else {
+				/* brasl to br, replace with basr + nop */
+				insnbuf[0] = 0x0d;
+			}
 			break;
 		}