Messages in this thread Patch in this message | | | Date | Tue, 19 Oct 2021 09:49:13 -0700 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 4/9] x86/alternative: Implement .retpoline_sites support |
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On Tue, Oct 19, 2021 at 09:47:02AM -0700, Josh Poimboeuf wrote: > On Tue, Oct 19, 2021 at 01:37:09PM +0200, Peter Zijlstra wrote: > > On Wed, Oct 13, 2021 at 01:52:59PM -0700, Josh Poimboeuf wrote: > > > > > BTW, CALL_NOSPEC results in a retpoline site in .altinstr_replacement: > > > > > > Relocation section [40] '.rela.retpoline_sites' for section [39] '.retpoline_sites' at offset 0x8d28 contains 1 entry: > > > Offset Type Value Addend Name > > > 000000000000000000 X86_64_PC32 000000000000000000 +10 .altinstr_replacement > > > > > > Which I assume we don't want. > > > > (I missed this initially, and just independently rediscovered it) > > > > In principle this problem affects static_call_list, the __sanitizer_cov_ > > and __fentry__ and now retpoline_sites. > > > > Granted, it seems really unlikely to find __fentry__ or __sanitizer_cov_ > > references in alternatives, but it should be trivial to manually create > > one. > > > > I'm thinking we want to exclude all those when found in > > .altinstr_replacement, right? It just doesn't make sense to rewrite > > replacement text. > > Right. > > (Someday, if it made sense to do so, objtool could put the annotation at > the original replaced instruction. Then the kernel self-patching code > could run after alternatives patching and could then decide whether the > annotation is relevant or not. But right now I can't think of any > scenario where that would be remotely sane.) > > > How is something like the below? (I'm not completely happy with it, but > > I couldn't think of something better either). > > How about something like this?
Slightly improved version:
diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 7c865a10372a..e0892632ef4a 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -993,18 +993,28 @@ static void remove_insn_ops(struct instruction *insn) } } -static void add_call_dest(struct objtool_file *file, struct instruction *insn, - struct symbol *dest, bool sibling) +static void annotate_call_site(struct objtool_file *file, + struct instruction *insn, bool sibling) { struct reloc *reloc = insn_reloc(file, insn); - insn->call_dest = dest; - if (!dest) + /* + * Alternative replacement code is just template code which is + * sometimes copied to the original instruction. For now, don't + * annotate it. (In the future we might consider annotating the + * original instruction if/when it ever makes sense to do so.) + */ + if (!strcmp(insn->sec->name, ".altinstr_replacement")) return; + if (insn->call_dest->retpoline) { + list_add_tail(&insn->call_node, &file->retpoline_call_list); + return; + } + if (insn->call_dest->static_call_tramp) { - list_add_tail(&insn->call_node, - &file->static_call_list); + list_add_tail(&insn->call_node, &file->static_call_list); + return; } /* @@ -1025,6 +1035,7 @@ static void add_call_dest(struct objtool_file *file, struct instruction *insn, : arch_nop_insn(insn->len)); insn->type = sibling ? INSN_RETURN : INSN_NOP; + return; } if (mcount && !strcmp(insn->call_dest->name, "__fentry__")) { @@ -1042,9 +1053,19 @@ static void add_call_dest(struct objtool_file *file, struct instruction *insn, insn->type = INSN_NOP; - list_add_tail(&insn->mcount_loc_node, - &file->mcount_loc_list); + list_add_tail(&insn->mcount_loc_node, &file->mcount_loc_list); + return; } +} + +static void add_call_dest(struct objtool_file *file, struct instruction *insn, + struct symbol *dest, bool sibling) +{ + insn->call_dest = dest; + if (!dest) + return; + + annotate_call_site(file, insn, sibling); /* * Whatever stack impact regular CALLs have, should be undone @@ -1054,6 +1075,7 @@ static void add_call_dest(struct objtool_file *file, struct instruction *insn, * are converted to JUMP, see read_intra_function_calls(). */ remove_insn_ops(insn); + } /* @@ -1077,7 +1099,7 @@ static int add_jump_destinations(struct objtool_file *file) } else if (reloc->sym->type == STT_SECTION) { dest_sec = reloc->sym->sec; dest_off = arch_dest_reloc_offset(reloc->addend); - } else if (arch_is_retpoline(reloc->sym)) { + } else if (reloc->sym->retpoline) { /* * Retpoline jumps are really dynamic jumps in * disguise, so convert them accordingly. @@ -1087,9 +1109,7 @@ static int add_jump_destinations(struct objtool_file *file) else insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL; - list_add_tail(&insn->call_node, - &file->retpoline_call_list); - + add_call_dest(file, insn, reloc->sym, true); insn->retpoline_safe = true; continue; } else if (insn->func) { @@ -1218,20 +1238,14 @@ static int add_call_destinations(struct objtool_file *file) add_call_dest(file, insn, dest, false); - } else if (arch_is_retpoline(reloc->sym)) { + } else if (reloc->sym->retpoline) { /* * Retpoline calls are really dynamic calls in * disguise, so convert them accordingly. */ insn->type = INSN_CALL_DYNAMIC; + add_call_dest(file, insn, reloc->sym, false); insn->retpoline_safe = true; - - list_add_tail(&insn->call_node, - &file->retpoline_call_list); - - remove_insn_ops(insn); - continue; - } else add_call_dest(file, insn, reloc->sym, false); } @@ -1916,8 +1930,25 @@ static int read_static_call_tramps(struct objtool_file *file) list_for_each_entry(func, &sec->symbol_list, list) { if (func->bind == STB_GLOBAL && !strncmp(func->name, STATIC_CALL_TRAMP_PREFIX_STR, - strlen(STATIC_CALL_TRAMP_PREFIX_STR))) + strlen(STATIC_CALL_TRAMP_PREFIX_STR))) { func->static_call_tramp = true; + } + } + } + + return 0; +} + +static int read_retpoline_thunks(struct objtool_file *file) +{ + struct section *sec; + struct symbol *func; + + for_each_sec(file, sec) { + list_for_each_entry(func, &sec->symbol_list, list) { + if (func->bind == STB_GLOBAL && arch_is_retpoline(func)) { + func->retpoline = true; + } } } @@ -1980,13 +2011,16 @@ static int decode_sections(struct objtool_file *file) if (ret) return ret; - /* - * Must be before add_{jump_call}_destination. - */ + /* Must be before add_{jump_call}_destination. */ ret = read_static_call_tramps(file); if (ret) return ret; + /* Must be before add_{jump_call}_destination. */ + ret = read_retpoline_thunks(file); + if (ret) + return ret; + /* * Must be before add_special_section_alts() as that depends on * jump_dest being set. diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index 9bdc7c757bf8..b773366dfb52 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -56,6 +56,7 @@ struct symbol { struct symbol *pfunc, *cfunc, *alias; bool uaccess_safe; bool static_call_tramp; + bool retpoline; struct list_head pv_target; };
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