bpf, riscv: clear target register high 32-bits for and/or/xor on ALU32

When using 32-bit subregisters (ALU32), the RISC-V JIT would not clear
the high 32-bits of the target register and therefore generate
incorrect code.

E.g., in the following code:

  $ cat test.c
  unsigned int f(unsigned long long a,
  	       unsigned int b)
  {
  	return (unsigned int)a & b;
  }

  $ clang-9 -target bpf -O2 -emit-llvm -S test.c -o - | \
  	llc-9 -mattr=+alu32 -mcpu=v3
  	.text
  	.file	"test.c"
  	.globl	f
  	.p2align	3
  	.type	f,@function
  f:
  	r0 = r1
  	w0 &= w2
  	exit
  .Lfunc_end0:
  	.size	f, .Lfunc_end0-f

The JIT would not clear the high 32-bits of r0 after the
and-operation, which in this case might give an incorrect return
value.

After this patch, that is not the case, and the upper 32-bits are
cleared.
Reported-by: Jiong Wang <jiong.wang@netronome.com>
Fixes: 2353ecc6 ("bpf, riscv: add BPF JIT for RV64G")
Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

arch/riscv/net/bpf_jit_comp.c

@@ -759,14 +759,20 @@ static int emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 	case BPF_ALU | BPF_AND | BPF_X:
 	case BPF_ALU64 | BPF_AND | BPF_X:
 		emit(rv_and(rd, rd, rs), ctx);
+		if (!is64)
+			emit_zext_32(rd, ctx);
 		break;
 	case BPF_ALU | BPF_OR | BPF_X:
 	case BPF_ALU64 | BPF_OR | BPF_X:
 		emit(rv_or(rd, rd, rs), ctx);
+		if (!is64)
+			emit_zext_32(rd, ctx);
 		break;
 	case BPF_ALU | BPF_XOR | BPF_X:
 	case BPF_ALU64 | BPF_XOR | BPF_X:
 		emit(rv_xor(rd, rd, rs), ctx);
+		if (!is64)
+			emit_zext_32(rd, ctx);
 		break;
 	case BPF_ALU | BPF_MUL | BPF_X:
 	case BPF_ALU64 | BPF_MUL | BPF_X: