bpf: Allow instructions with arena source and non-arena dest registers

[ Upstream commit ac61bff ]

The compiler sometimes stores the result of a PTR_TO_ARENA and SCALAR
operation into the scalar register rather than the pointer register.
Relax the verifier to allow operations between a source arena register
and a destination non-arena register, marking the destination's value
as a PTR_TO_ARENA.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Acked-by: Song Liu <song@kernel.org>
Fixes: 6082b6c ("bpf: Recognize addr_space_cast instruction in the verifier.")
Link: https://lore.kernel.org/r/20260412174546.18684-2-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: etsal

kernel/bpf/verifier.c

@@ -15705,11 +15705,20 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
 	int err;
 
 	dst_reg = &regs[insn->dst_reg];
-	src_reg = NULL;
+	if (BPF_SRC(insn->code) == BPF_X)
+		src_reg = &regs[insn->src_reg];
+	else
+		src_reg = NULL;
 
-	if (dst_reg->type == PTR_TO_ARENA) {
+	/* Case where at least one operand is an arena. */
+	if (dst_reg->type == PTR_TO_ARENA || (src_reg && src_reg->type == PTR_TO_ARENA)) {
 		struct bpf_insn_aux_data *aux = cur_aux(env);
 
+		if (dst_reg->type != PTR_TO_ARENA)
+			*dst_reg = *src_reg;
+
+		dst_reg->subreg_def = env->insn_idx + 1;
+
 		if (BPF_CLASS(insn->code) == BPF_ALU64)
 			/*
 			 * 32-bit operations zero upper bits automatically.
@@ -15725,7 +15734,6 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env,
 		ptr_reg = dst_reg;
 
 	if (BPF_SRC(insn->code) == BPF_X) {
-		src_reg = &regs[insn->src_reg];
 		if (src_reg->type != SCALAR_VALUE) {
 			if (dst_reg->type != SCALAR_VALUE) {
 				/* Combining two pointers by any ALU op yields