bpf: interpreter support BPF_ALU | BPF_ARSH

This patch implements interpreting BPF_ALU | BPF_ARSH. Do arithmetic right
shift on low 32-bit sub-register, and zero the high 32 bits.
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/core.c

@@ -942,6 +942,7 @@ EXPORT_SYMBOL_GPL(__bpf_call_base);
 	INSN_3(ALU, XOR,  X),			\
 	INSN_3(ALU, MUL,  X),			\
 	INSN_3(ALU, MOV,  X),			\
+	INSN_3(ALU, ARSH, X),			\
 	INSN_3(ALU, DIV,  X),			\
 	INSN_3(ALU, MOD,  X),			\
 	INSN_2(ALU, NEG),			\
@@ -957,6 +958,7 @@ EXPORT_SYMBOL_GPL(__bpf_call_base);
 	INSN_3(ALU, XOR,  K),			\
 	INSN_3(ALU, MUL,  K),			\
 	INSN_3(ALU, MOV,  K),			\
+	INSN_3(ALU, ARSH, K),			\
 	INSN_3(ALU, DIV,  K),			\
 	INSN_3(ALU, MOD,  K),			\
 	/* 64 bit ALU operations. */		\
@@ -1137,6 +1139,12 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 		DST = (u64) (u32) insn[0].imm | ((u64) (u32) insn[1].imm) << 32;
 		insn++;
 		CONT;
+	ALU_ARSH_X:
+		DST = (u64) (u32) ((*(s32 *) &DST) >> SRC);
+		CONT;
+	ALU_ARSH_K:
+		DST = (u64) (u32) ((*(s32 *) &DST) >> IMM);
+		CONT;
 	ALU64_ARSH_X:
 		(*(s64 *) &DST) >>= SRC;
 		CONT;