Later commits will disallow runtime-mutable text in .noinstr sections in order to safely defer instruction patching IPIs.
All static keys used in .noinstr sections have now been checked as being either flagged as __ro_after_init, or as forceful static keys. Any occurrence of this new warning would be the result of a code change that will need looking at.
Suggested-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Valentin Schneider vschneid@redhat.com --- offset_of(static_key.type) and JUMP_TYPE_FORCEFUL would need to be shoved into a somewhat standalone header file that could be included by objtool itself. --- tools/objtool/Documentation/objtool.txt | 13 ++++++++ tools/objtool/check.c | 41 +++++++++++++++++++++++++ tools/objtool/include/objtool/check.h | 1 + tools/objtool/include/objtool/special.h | 2 ++ tools/objtool/special.c | 3 ++ 5 files changed, 60 insertions(+)
diff --git a/tools/objtool/Documentation/objtool.txt b/tools/objtool/Documentation/objtool.txt index 7c3ee959b63c7..06fa285873387 100644 --- a/tools/objtool/Documentation/objtool.txt +++ b/tools/objtool/Documentation/objtool.txt @@ -447,6 +447,19 @@ the objtool maintainers. names and does not use module_init() / module_exit() macros to create them.
+13. file.o: warning: func()+0x2a: non __ro_after_init static key "key" in .noinstr section + + This means that the noinstr function func() uses a static key that can be + modified at runtime. This is not allowed as noinstr functions rely on + containing stable instructions after init. + + Check whether the static key in question can really be modified at runtime, + and if it is only enabled during init then mark it as __ro_after_init. If it + genuinely needs to be modified at runtime: + + 1) Directly rely on the underlying atomic count of they key in the noinstr + functions. + 2) Mark the static key as forceful.
If the error doesn't seem to make sense, it could be a bug in objtool. Feel free to ask the objtool maintainer for help. diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 00e25492f5065..c1fb02c326839 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2056,6 +2056,9 @@ static int add_special_section_alts(struct objtool_file *file) alt->next = orig_insn->alts; orig_insn->alts = alt;
+ if (special_alt->key_sym) + orig_insn->key_sym = special_alt->key_sym; + list_del(&special_alt->list); free(special_alt); } @@ -3605,6 +3608,41 @@ static int validate_return(struct symbol *func, struct instruction *insn, struct return 0; }
+static bool static_key_is_forceful(struct symbol *key) +{ + if (!strcmp(key->sec->name, ".data")) { + unsigned long data_offset = key->sec->data->d_off; + unsigned long key_offset = key->sym.st_value; + char* data = key->sec->data->d_buf; + + /* + * offset_of(static_key.type) + * v + * v JUMP_TYPE_FORCEFUL + * v v + */ + return data[(key_offset + 8) - data_offset] & 0x4; + } + + return false; +} + +static int validate_static_key(struct instruction *insn, struct insn_state *state) +{ + if (state->noinstr && state->instr <= 0) { + if (static_key_is_forceful(insn->key_sym)) + return 0; + + if ((strcmp(insn->key_sym->sec->name, ".data..ro_after_init"))) { + WARN_INSN(insn, "non __ro_after_init static key "%s" in .noinstr section", + insn->key_sym->name); + return 1; + } + } + + return 0; +} + static struct instruction *next_insn_to_validate(struct objtool_file *file, struct instruction *insn) { @@ -3766,6 +3804,9 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, if (handle_insn_ops(insn, next_insn, &state)) return 1;
+ if (insn->key_sym) + validate_static_key(insn, &state); + switch (insn->type) {
case INSN_RETURN: diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h index daa46f1f0965a..35dd21f8f41e1 100644 --- a/tools/objtool/include/objtool/check.h +++ b/tools/objtool/include/objtool/check.h @@ -77,6 +77,7 @@ struct instruction { struct symbol *sym; struct stack_op *stack_ops; struct cfi_state *cfi; + struct symbol *key_sym; };
static inline struct symbol *insn_func(struct instruction *insn) diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h index 86d4af9c5aa9d..0e61f34fe3a28 100644 --- a/tools/objtool/include/objtool/special.h +++ b/tools/objtool/include/objtool/special.h @@ -27,6 +27,8 @@ struct special_alt { struct section *new_sec; unsigned long new_off;
+ struct symbol *key_sym; + unsigned int orig_len, new_len; /* group only */ };
diff --git a/tools/objtool/special.c b/tools/objtool/special.c index 097a69db82a0e..fefab2b471bf8 100644 --- a/tools/objtool/special.c +++ b/tools/objtool/special.c @@ -127,6 +127,9 @@ static int get_alt_entry(struct elf *elf, const struct special_entry *entry, return -1; } alt->key_addend = reloc_addend(key_reloc); + + reloc_to_sec_off(key_reloc, &sec, &offset); + alt->key_sym = find_symbol_by_offset(sec, offset & ~3); }
return 0;