selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 119 insertions, 0 deletions

diff --git a/tools/objtool/klp-symid.c b/tools/objtool/klp-symid.c
new file mode 100644
index 000000000..b19f76dff
--- /dev/null
+++ b/tools/objtool/klp-symid.c
@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Emit the .klp.symid table which allows "objtool klp diff" to reliably
+ * disambiguate duplicate-named local symbols in vmlinux.
+ *
+ * Livepatch identifies a duplicate-named symbol by its position (sympos)
+ * among the same-named kallsyms entries, counted in ascending address order
+ * in the final linked vmlinux.  That order can't be derived from vmlinux.o
+ * alone: the final link reorders sub-sections (.text.unlikely*, .data..*,
+ * etc).
+ *
+ * Bridge the gap with a table which survives the final link: a single
+ * non-alloc section containing an array of { id, addr } entries, where
+ * 'id' is a unique counter identifier and 'addr' has a relocation to the
+ * symbol.  The linker copies 'id' verbatim and resolves 'addr' to the symbol's
+ * final address.
+ *
+ * The table is only emitted for vmlinux.o, and only when klp-build asks for it
+ * with KLP_SYMIDS=1, which adds --klp-symids to the vmlinux.o objtool run.
+ *
+ * It can't survive --gc-sections, which sweeps the whole section; klp-build
+ * rejects CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.
+ */
+#include <linux/string.h>
+
+#include <objtool/objtool.h>
+#include <objtool/warn.h>
+#include <objtool/endianness.h>
+#include <objtool/klp.h>
+
+static const char * const discarded_secs[] = {
+	".discard",
+	".exitcall.exit",
+	".modinfo",
+	".no_trim_symbol",
+	"__tracepoint_check",
+};
+
+static bool discarded_sec(struct section *sec)
+{
+	if (!(sec->sh.sh_flags & SHF_ALLOC))
+		return true;
+
+	for (int i = 0; i < ARRAY_SIZE(discarded_secs); i++)
+		if (strstarts(sec->name, discarded_secs[i]))
+			return true;
+
+	return false;
+}
+
+static bool symid_needed(struct elf *elf, struct symbol *sym)
+{
+	struct symbol *s;
+
+	if (!is_local_sym(sym) || is_undef_sym(sym))
+		return false;
+
+	if (!is_func_sym(sym) && !is_object_sym(sym))
+		return false;
+
+	if (is_prefix_func(sym))
+		return false;
+
+	if (discarded_sec(sym->sec))
+		return false;
+
+	for_each_sym_by_name(elf, sym->name, s) {
+		if (s == sym || is_sec_sym(s) || is_file_sym(s) || is_undef_sym(s))
+			continue;
+		return true;
+	}
+
+	return false;
+}
+
+int klp_create_symid_sections(struct objtool_file *file)
+{
+	struct elf *elf = file->elf;
+	struct klp_symid *symids;
+	struct section *sec;
+	struct symbol *sym;
+	u64 nr = 0, i = 0;
+
+	if (!str_ends_with(objname, "vmlinux.o"))
+		return 0;
+
+	for_each_sym(elf, sym)
+		if (symid_needed(elf, sym))
+			nr++;
+
+	if (!nr)
+		return 0;
+
+	sec = elf_create_section(elf, KLP_SYMID_SEC, 0, sizeof(struct klp_symid),
+				 SHT_PROGBITS, 8, 0);
+	if (!sec)
+		return -1;
+
+	symids = elf_add_data(elf, sec, NULL, nr * sizeof(struct klp_symid));
+	if (!symids)
+		return -1;
+
+	for_each_sym(elf, sym) {
+		if (!symid_needed(elf, sym))
+			continue;
+
+		symids[i].id = bswap_if_needed(elf, i);
+
+		if (!elf_create_reloc(elf, sec,
+				      i * sizeof(struct klp_symid) +
+				      offsetof(struct klp_symid, addr),
+				      sym, 0, R_ABS64))
+			return -1;
+
+		i++;
+	}
+
+	return 0;
+}