bpf, arm64: Add support for signed arena loads

Add support for signed loads from arena which are internally converted
to loads with mode set BPF_PROBE_MEM32SX by the verifier. The
implementation is similar to BPF_PROBE_MEMSX and BPF_MEMSX but for
BPF_PROBE_MEM32SX, arena_vm_base is added to the src register to form
the address.

Signed-off-by: Puranjay Mohan <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: puranjaymohan

arch/arm64/net/bpf_jit_comp.c

@@ -1133,12 +1133,14 @@ static int add_exception_handler(const struct bpf_insn *insn,
 		return 0;
 
 	if (BPF_MODE(insn->code) != BPF_PROBE_MEM &&
-		BPF_MODE(insn->code) != BPF_PROBE_MEMSX &&
-			BPF_MODE(insn->code) != BPF_PROBE_MEM32 &&
-				BPF_MODE(insn->code) != BPF_PROBE_ATOMIC)
+	    BPF_MODE(insn->code) != BPF_PROBE_MEMSX &&
+	    BPF_MODE(insn->code) != BPF_PROBE_MEM32 &&
+	    BPF_MODE(insn->code) != BPF_PROBE_MEM32SX &&
+	    BPF_MODE(insn->code) != BPF_PROBE_ATOMIC)
 		return 0;
 
 	is_arena = (BPF_MODE(insn->code) == BPF_PROBE_MEM32) ||
+		   (BPF_MODE(insn->code) == BPF_PROBE_MEM32SX) ||
 		   (BPF_MODE(insn->code) == BPF_PROBE_ATOMIC);
 
 	if (!ctx->prog->aux->extable ||
@@ -1659,7 +1661,11 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 	case BPF_LDX | BPF_PROBE_MEM32 | BPF_H:
 	case BPF_LDX | BPF_PROBE_MEM32 | BPF_W:
 	case BPF_LDX | BPF_PROBE_MEM32 | BPF_DW:
-		if (BPF_MODE(insn->code) == BPF_PROBE_MEM32) {
+	case BPF_LDX | BPF_PROBE_MEM32SX | BPF_B:
+	case BPF_LDX | BPF_PROBE_MEM32SX | BPF_H:
+	case BPF_LDX | BPF_PROBE_MEM32SX | BPF_W:
+		if (BPF_MODE(insn->code) == BPF_PROBE_MEM32 ||
+		    BPF_MODE(insn->code) == BPF_PROBE_MEM32SX) {
 			emit(A64_ADD(1, tmp2, src, arena_vm_base), ctx);
 			src = tmp2;
 		}
@@ -1671,7 +1677,8 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 			off_adj = off;
 		}
 		sign_extend = (BPF_MODE(insn->code) == BPF_MEMSX ||
-				BPF_MODE(insn->code) == BPF_PROBE_MEMSX);
+				BPF_MODE(insn->code) == BPF_PROBE_MEMSX ||
+				 BPF_MODE(insn->code) == BPF_PROBE_MEM32SX);
 		switch (BPF_SIZE(code)) {
 		case BPF_W:
 			if (is_lsi_offset(off_adj, 2)) {
@@ -1879,9 +1886,11 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 		if (ret)
 			return ret;
 
-		ret = add_exception_handler(insn, ctx, dst);
-		if (ret)
-			return ret;
+		if (BPF_MODE(insn->code) == BPF_PROBE_ATOMIC) {
+			ret = add_exception_handler(insn, ctx, dst);
+			if (ret)
+				return ret;
+		}
 		break;
 
 	default:
@@ -3064,11 +3073,6 @@ bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena)
 		if (!bpf_atomic_is_load_store(insn) &&
 		    !cpus_have_cap(ARM64_HAS_LSE_ATOMICS))
 			return false;
-		break;
-	case BPF_LDX | BPF_MEMSX | BPF_B:
-	case BPF_LDX | BPF_MEMSX | BPF_H:
-	case BPF_LDX | BPF_MEMSX | BPF_W:
-		return false;
 	}
 	return true;
 }