libbpf: Turn relo_core->sym_off unsigned

The symbols' relocation offsets in BPF are stored in an int field,
but cannot actually be negative. When in the next patch libbpf relocates
globals to the end of the arena, it is also possible to have valid
offsets > 2GiB that are used to calculate the final relo offsets.
Avoid accidentally interpreting large offsets as negative by turning
the sym_off field unsigned.

Signed-off-by: Emil Tsalapatis <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Acked-by: Eduard Zingerman <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: etsal

tools/lib/bpf/libbpf.c

@@ -380,7 +380,7 @@ struct reloc_desc {
 		const struct bpf_core_relo *core_relo; /* used when type == RELO_CORE */
 		struct {
 			int map_idx;
-			int sym_off;
+			unsigned int sym_off;
 			/*
 			 * The following two fields can be unionized, as the
 			 * ext_idx field is used for extern symbols, and the
@@ -763,7 +763,7 @@ struct bpf_object {
 
 	struct {
 		struct bpf_program *prog;
-		int sym_off;
+		unsigned int sym_off;
 		int fd;
 	} *jumptable_maps;
 	size_t jumptable_map_cnt;
@@ -6192,7 +6192,7 @@ static void poison_kfunc_call(struct bpf_program *prog, int relo_idx,
 	insn->imm = POISON_CALL_KFUNC_BASE + ext_idx;
 }
 
-static int find_jt_map(struct bpf_object *obj, struct bpf_program *prog, int sym_off)
+static int find_jt_map(struct bpf_object *obj, struct bpf_program *prog, unsigned int sym_off)
 {
 	size_t i;
 
@@ -6210,7 +6210,7 @@ static int find_jt_map(struct bpf_object *obj, struct bpf_program *prog, int sym
 	return -ENOENT;
 }
 
-static int add_jt_map(struct bpf_object *obj, struct bpf_program *prog, int sym_off, int map_fd)
+static int add_jt_map(struct bpf_object *obj, struct bpf_program *prog, unsigned int sym_off, int map_fd)
 {
 	size_t cnt = obj->jumptable_map_cnt;
 	size_t size = sizeof(obj->jumptable_maps[0]);
@@ -6244,7 +6244,7 @@ static int find_subprog_idx(struct bpf_program *prog, int insn_idx)
 static int create_jt_map(struct bpf_object *obj, struct bpf_program *prog, struct reloc_desc *relo)
 {
 	const __u32 jt_entry_size = 8;
-	int sym_off = relo->sym_off;
+	unsigned int sym_off = relo->sym_off;
 	int jt_size = relo->sym_size;
 	__u32 max_entries = jt_size / jt_entry_size;
 	__u32 value_size = sizeof(struct bpf_insn_array_value);
@@ -6260,7 +6260,7 @@ static int create_jt_map(struct bpf_object *obj, struct bpf_program *prog, struc
 		return map_fd;
 
 	if (sym_off % jt_entry_size) {
-		pr_warn("map '.jumptables': jumptable start %d should be multiple of %u\n",
+		pr_warn("map '.jumptables': jumptable start %u should be multiple of %u\n",
 			sym_off, jt_entry_size);
 		return -EINVAL;
 	}
@@ -6316,7 +6316,7 @@ static int create_jt_map(struct bpf_object *obj, struct bpf_program *prog, struc
 		 * should contain values that fit in u32.
 		 */
 		if (insn_off > UINT32_MAX) {
-			pr_warn("map '.jumptables': invalid jump table value 0x%llx at offset %d\n",
+			pr_warn("map '.jumptables': invalid jump table value 0x%llx at offset %u\n",
 				(long long)jt[i], sym_off + i * jt_entry_size);
 			err = -EINVAL;
 			goto err_close;