From 6668ed271eaefaa63e686bdfbedaeb7b8e492722 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 10:43:19 +0200 Subject: selftests/bpf: Reject graph kptr use after RCU unlock 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 Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- tools/objtool/klp-symid.c | 119 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 119 insertions(+) create mode 100644 tools/objtool/klp-symid.c (limited to 'tools/objtool/klp-symid.c') 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 + +#include +#include +#include +#include + +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; +} -- cgit v1.3.1