From: Josh Poimboeuf jpoimboe@kernel.org
Warn about static branches/calls in noinstr regions, unless the corresponding key is RO-after-init or has been manually whitelisted with DEFINE_STATIC_KEY_*_NOINSTR(().
Signed-off-by: Josh Poimboeuf jpoimboe@kernel.org [Added NULL check for insn_call_dest() return value] Signed-off-by: Valentin Schneider vschneid@redhat.com --- include/linux/jump_label.h | 17 +++-- include/linux/objtool.h | 7 ++ include/linux/static_call.h | 3 + tools/objtool/Documentation/objtool.txt | 34 +++++++++ tools/objtool/check.c | 92 ++++++++++++++++++++++--- tools/objtool/include/objtool/check.h | 1 + tools/objtool/include/objtool/elf.h | 1 + tools/objtool/include/objtool/special.h | 1 + tools/objtool/special.c | 18 ++++- 9 files changed, 156 insertions(+), 18 deletions(-)
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h index 88bb6e32fdcbc..dc8a82a62c109 100644 --- a/include/linux/jump_label.h +++ b/include/linux/jump_label.h @@ -75,6 +75,7 @@
#include <linux/types.h> #include <linux/compiler.h> +#include <linux/objtool.h>
extern bool static_key_initialized;
@@ -373,8 +374,9 @@ struct static_key_false { #define DEFINE_STATIC_KEY_TRUE(name) \ struct static_key_true name = STATIC_KEY_TRUE_INIT
-#define DEFINE_STATIC_KEY_TRUE_RO(name) \ - struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT +#define DEFINE_STATIC_KEY_TRUE_RO(name) \ + struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT; \ + ANNOTATE_NOINSTR_ALLOWED(name)
#define DECLARE_STATIC_KEY_TRUE(name) \ extern struct static_key_true name @@ -382,8 +384,9 @@ struct static_key_false { #define DEFINE_STATIC_KEY_FALSE(name) \ struct static_key_false name = STATIC_KEY_FALSE_INIT
-#define DEFINE_STATIC_KEY_FALSE_RO(name) \ - struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT +#define DEFINE_STATIC_KEY_FALSE_RO(name) \ + struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT; \ + ANNOTATE_NOINSTR_ALLOWED(name)
/* * The _NOINSTR variants are used to tell objtool the static key is allowed to @@ -397,10 +400,12 @@ struct static_key_false { * definition with the rationale. */ #define DEFINE_STATIC_KEY_TRUE_NOINSTR(name) \ - DEFINE_STATIC_KEY_TRUE(name) + DEFINE_STATIC_KEY_TRUE(name); \ + ANNOTATE_NOINSTR_ALLOWED(name)
#define DEFINE_STATIC_KEY_FALSE_NOINSTR(name) \ - DEFINE_STATIC_KEY_FALSE(name) + DEFINE_STATIC_KEY_FALSE(name); \ + ANNOTATE_NOINSTR_ALLOWED(name)
#define DECLARE_STATIC_KEY_FALSE(name) \ extern struct static_key_false name diff --git a/include/linux/objtool.h b/include/linux/objtool.h index b3b8d3dab52d5..1a7389f273063 100644 --- a/include/linux/objtool.h +++ b/include/linux/objtool.h @@ -34,6 +34,12 @@ static void __used __section(".discard.func_stack_frame_non_standard") \ *__func_stack_frame_non_standard_##func = func
+#define __ANNOTATE_NOINSTR_ALLOWED(key) \ + static void __used __section(".discard.noinstr_allowed") \ + *__annotate_noinstr_allowed_##key = &key + +#define ANNOTATE_NOINSTR_ALLOWED(key) __ANNOTATE_NOINSTR_ALLOWED(key) + /* * STACK_FRAME_NON_STANDARD_FP() is a frame-pointer-specific function ignore * for the case where a function is intentionally missing frame pointer setup, @@ -157,6 +163,7 @@ #define STACK_FRAME_NON_STANDARD_FP(func) #define ANNOTATE_NOENDBR #define ASM_REACHABLE +#define ANNOTATE_NOINSTR_ALLOWED(key) #else #define ANNOTATE_INTRA_FUNCTION_CALL .macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0 diff --git a/include/linux/static_call.h b/include/linux/static_call.h index ea6ca57e2a829..0d4b16d348501 100644 --- a/include/linux/static_call.h +++ b/include/linux/static_call.h @@ -133,6 +133,7 @@
#include <linux/types.h> #include <linux/cpu.h> +#include <linux/objtool.h> #include <linux/static_call_types.h>
#ifdef CONFIG_HAVE_STATIC_CALL @@ -198,6 +199,7 @@ extern long __static_call_return0(void); .func = _func, \ .type = 1, \ }; \ + ANNOTATE_NOINSTR_ALLOWED(STATIC_CALL_TRAMP(name)); \ ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
#define DEFINE_STATIC_CALL_NULL(name, _func) \ @@ -214,6 +216,7 @@ extern long __static_call_return0(void); .func = NULL, \ .type = 1, \ }; \ + ANNOTATE_NOINSTR_ALLOWED(STATIC_CALL_TRAMP(name)); \ ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
#define DEFINE_STATIC_CALL_RET0(name, _func) \ diff --git a/tools/objtool/Documentation/objtool.txt b/tools/objtool/Documentation/objtool.txt index 7c3ee959b63c7..922d3b41541d0 100644 --- a/tools/objtool/Documentation/objtool.txt +++ b/tools/objtool/Documentation/objtool.txt @@ -447,6 +447,40 @@ the objtool maintainers. names and does not use module_init() / module_exit() macros to create them.
+13. file.o: warning: func()+0x2a: key: non-RO static key usage in noinstr code + file.o: warning: func()+0x2a: key: non-RO static call usage in noinstr code + + This means that noinstr function func() uses a static key or + static call named 'key' which can be modified at runtime. This is + discouraged because it prevents code patching IPIs from being + deferred. + + You have the following options: + + 1) Check whether the static key/call in question is only modified + during init. If so, define it as read-only-after-init with + DEFINE_STATIC_KEY_*_RO() or DEFINE_STATIC_CALL_RO(). + + 2) Avoid the runtime patching. For static keys this can be done by + using static_key_enabled() or by getting rid of the static key + altogether if performance is not a concern. + + For static calls, something like the following could be done: + + target = static_call_query(foo); + if (target == func1) + func1(); + else if (target == func2) + func2(); + ... + + 3) Silence the warning by defining the static key/call with + DEFINE_STATIC_*_NOINSTR(). This decision should not + be taken lightly as it may result in code patching IPIs getting + sent to isolated NOHZ_FULL CPUs running in pure userspace. A + comment should be added above the definition explaining the + rationale for the decision. +
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 6aa9259fc9940..24219538c1587 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1068,6 +1068,45 @@ static int create_direct_call_sections(struct objtool_file *file) return 0; }
+static int read_noinstr_allowed(struct objtool_file *file) +{ + struct section *rsec; + struct symbol *sym; + struct reloc *reloc; + + rsec = find_section_by_name(file->elf, ".rela.discard.noinstr_allowed"); + if (!rsec) + return 0; + + for_each_reloc(rsec, reloc) { + switch (reloc->sym->type) { + case STT_OBJECT: + case STT_FUNC: + sym = reloc->sym; + break; + + case STT_SECTION: + sym = find_symbol_by_offset(reloc->sym->sec, + reloc_addend(reloc)); + if (!sym) { + WARN_FUNC("can't find static key/call symbol", + reloc->sym->sec, reloc_addend(reloc)); + return -1; + } + break; + + default: + WARN("unexpected relocation symbol type in %s: %d", + rsec->name, reloc->sym->type); + return -1; + } + + sym->noinstr_allowed = 1; + } + + return 0; +} + /* * Warnings shouldn't be reported for ignored functions. */ @@ -1955,6 +1994,8 @@ static int handle_jump_alt(struct objtool_file *file, return -1; }
+ orig_insn->key = special_alt->key; + if (opts.hack_jump_label && special_alt->key_addend & 2) { struct reloc *reloc = insn_reloc(file, orig_insn);
@@ -2731,6 +2772,10 @@ static int decode_sections(struct objtool_file *file) if (ret) return ret;
+ ret = read_noinstr_allowed(file); + if (ret) + return ret; + return 0; }
@@ -3494,9 +3539,9 @@ static bool pv_call_dest(struct objtool_file *file, struct instruction *insn) return file->pv_ops[idx].clean; }
-static inline bool noinstr_call_dest(struct objtool_file *file, - struct instruction *insn, - struct symbol *func) +static inline bool noinstr_call_allowed(struct objtool_file *file, + struct instruction *insn, + struct symbol *func) { /* * We can't deal with indirect function calls at present; @@ -3516,10 +3561,10 @@ static inline bool noinstr_call_dest(struct objtool_file *file, return true;
/* - * If the symbol is a static_call trampoline, we can't tell. + * Only DEFINE_STATIC_CALL_*_RO allowed. */ if (func->static_call_tramp) - return true; + return func->noinstr_allowed;
/* * The __ubsan_handle_*() calls are like WARN(), they only happen when @@ -3532,14 +3577,29 @@ static inline bool noinstr_call_dest(struct objtool_file *file, return false; }
+static char *static_call_name(struct symbol *func) +{ + return func->name + strlen("__SCT__"); +} + static int validate_call(struct objtool_file *file, struct instruction *insn, struct insn_state *state) { - if (state->noinstr && state->instr <= 0 && - !noinstr_call_dest(file, insn, insn_call_dest(insn))) { - WARN_INSN(insn, "call to %s() leaves .noinstr.text section", call_dest_name(file, insn)); - return 1; + if (state->noinstr && state->instr <= 0) { + struct symbol *dest = insn_call_dest(insn); + + if (dest && dest->static_call_tramp) { + if (!dest->noinstr_allowed) { + WARN_INSN(insn, "%s: non-RO static call usage in noinstr", + static_call_name(dest)); + } + + } else if (dest && !noinstr_call_allowed(file, insn, dest)) { + WARN_INSN(insn, "call to %s() leaves .noinstr.text section", + call_dest_name(file, insn)); + return 1; + } }
if (state->uaccess && !func_uaccess_safe(insn_call_dest(insn))) { @@ -3604,6 +3664,17 @@ static int validate_return(struct symbol *func, struct instruction *insn, struct return 0; }
+static int validate_static_key(struct instruction *insn, struct insn_state *state) +{ + if (state->noinstr && state->instr <= 0 && !insn->key->noinstr_allowed) { + WARN_INSN(insn, "%s: non-RO static key usage in noinstr", + insn->key->name); + return 1; + } + + return 0; +} + static struct instruction *next_insn_to_validate(struct objtool_file *file, struct instruction *insn) { @@ -3765,6 +3836,9 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, if (handle_insn_ops(insn, next_insn, &state)) return 1;
+ if (insn->key) + 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..c0da7246eac7b 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; };
static inline struct symbol *insn_func(struct instruction *insn) diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index d7e815c2fd156..0cb79931262bb 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -69,6 +69,7 @@ struct symbol { u8 embedded_insn : 1; u8 local_label : 1; u8 frame_pointer : 1; + u8 noinstr_allowed : 1; struct list_head pv_target; struct reloc *relocs; }; diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h index 86d4af9c5aa9d..ce4759358ec48 100644 --- a/tools/objtool/include/objtool/special.h +++ b/tools/objtool/include/objtool/special.h @@ -20,6 +20,7 @@ struct special_alt { bool skip_alt; bool jump_or_nop; u8 key_addend; + struct symbol *key;
struct section *orig_sec; unsigned long orig_off; diff --git a/tools/objtool/special.c b/tools/objtool/special.c index 097a69db82a0e..982d5cb55e1bb 100644 --- a/tools/objtool/special.c +++ b/tools/objtool/special.c @@ -119,14 +119,26 @@ static int get_alt_entry(struct elf *elf, const struct special_entry *entry,
if (entry->key) { struct reloc *key_reloc; + struct symbol *key; + s64 key_addend;
key_reloc = find_reloc_by_dest(elf, sec, offset + entry->key); if (!key_reloc) { - WARN_FUNC("can't find key reloc", - sec, offset + entry->key); + WARN_FUNC("can't find key reloc", sec, offset + entry->key); return -1; } - alt->key_addend = reloc_addend(key_reloc); + + key = key_reloc->sym; + key_addend = reloc_addend(key_reloc); + + if (key->type == STT_SECTION) + key = find_symbol_by_offset(key->sec, key_addend & ~3); + + /* embedded keys not supported */ + if (key) { + alt->key = key; + alt->key_addend = key_addend; + } }
return 0;