Messages in this thread Patch in this message | | | Date | Thu, 16 Apr 2020 17:07:56 +0200 | From | Peter Zijlstra <> | Subject | [RFC][PATCH 4/7] objtool: Add support for intra-function calls |
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From: Alexandre Chartre <alexandre.chartre@oracle.com>
Change objtool to support intra-function calls. On x86, an intra-function call is represented in objtool as a push onto the stack (of the return address), and a jump to the destination address. That way the stack information is correctly updated and the call flow is still accurate.
Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200414103618.12657-4-alexandre.chartre@oracle.com --- include/linux/frame.h | 11 + tools/objtool/Documentation/stack-validation.txt | 8 + tools/objtool/arch/x86/decode.c | 17 ++- tools/objtool/check.c | 129 ++++++++++++++++++----- tools/objtool/check.h | 1 5 files changed, 140 insertions(+), 26 deletions(-)
--- a/include/linux/frame.h +++ b/include/linux/frame.h @@ -15,9 +15,20 @@ static void __used __section(.discard.func_stack_frame_non_standard) \ *__func_stack_frame_non_standard_##func = func +/* + * This macro indicates that the following intra-function call is valid. + * Any non-annotated intra-function call will cause objtool to issue warning. + */ +#define ANNOTATE_INTRA_FUNCTION_CALL \ + 999: \ + .pushsection .discard.intra_function_calls; \ + .long 999b; \ + .popsection; + #else /* !CONFIG_STACK_VALIDATION */ #define STACK_FRAME_NON_STANDARD(func) +#define ANNOTATE_INTRA_FUNCTION_CALL #endif /* CONFIG_STACK_VALIDATION */ --- a/tools/objtool/Documentation/stack-validation.txt +++ b/tools/objtool/Documentation/stack-validation.txt @@ -290,6 +290,14 @@ they mean, and suggestions for how to fi https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646 +9. file.o: warning: unsupported intra-function call + + This warning means that a direct call is done to a destination which + is not at the beginning of a function. If this is a legit call, you + can remove this warning by putting the ANNOTATE_INTRA_FUNCTION_CALL + directive right before the call. + + 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. --- a/tools/objtool/arch/x86/decode.c +++ b/tools/objtool/arch/x86/decode.c @@ -453,6 +453,12 @@ int arch_decode_instruction(struct elf * case 0xe8: *type = INSN_CALL; + /* + * For the impact on the stack, a call behaves like + * a push of an immediate value (the return address). + */ + op->src.type = OP_SRC_CONST; + op->dest.type = OP_DEST_PUSH; break; case 0xfc: @@ -493,10 +499,17 @@ int arch_decode_instruction(struct elf * *immediate = insn.immediate.nbytes ? insn.immediate.value : 0; - if (*type == INSN_STACK || *type == INSN_EXCEPTION_RETURN) + switch (*type) { + case INSN_STACK: + case INSN_EXCEPTION_RETURN: + case INSN_CALL: list_add_tail(&op->list, ops_list); - else + break; + + default: free(op); + break; + } return 0; } --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -691,44 +691,51 @@ static int add_jump_destinations(struct return 0; } +static int setup_call_dest(struct objtool_file *file, struct instruction *insn) +{ + unsigned long dest_off; + + dest_off = insn->offset + insn->len + insn->immediate; + insn->call_dest = find_func_by_offset(insn->sec, dest_off); + if (!insn->call_dest) + insn->call_dest = find_symbol_by_offset(insn->sec, dest_off); + + if (!insn->call_dest) { + /* intra-function call */ + if (insn->intra_function_call) + return 0; + + WARN_FUNC("intra-function call", insn->sec, insn->offset); + return -1; + } + + /* regular call */ + if (insn->func && insn->call_dest->type != STT_FUNC) { + WARN_FUNC("unsupported call to non-function", + insn->sec, insn->offset); + return -1; + } + + return 0; +} + /* * Find the destination instructions for all calls. */ static int add_call_destinations(struct objtool_file *file) { struct instruction *insn; - unsigned long dest_off; struct rela *rela; for_each_insn(file, insn) { - if (insn->type != INSN_CALL) + if (insn->type != INSN_CALL || insn->ignore) continue; rela = find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len); if (!rela) { - dest_off = insn->offset + insn->len + insn->immediate; - insn->call_dest = find_func_by_offset(insn->sec, dest_off); - if (!insn->call_dest) - insn->call_dest = find_symbol_by_offset(insn->sec, dest_off); - - if (insn->ignore) - continue; - - if (!insn->call_dest) { - WARN_FUNC("unsupported intra-function call", - insn->sec, insn->offset); - if (retpoline) - WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE."); - return -1; - } - - if (insn->func && insn->call_dest->type != STT_FUNC) { - WARN_FUNC("unsupported call to non-function", - insn->sec, insn->offset); + if (setup_call_dest(file, insn)) return -1; - } - } else if (rela->sym->type == STT_SECTION) { insn->call_dest = find_func_by_offset(rela->sym->sec, rela->addend+4); @@ -1414,6 +1421,52 @@ static int read_instr_hints(struct objto return 0; } +static int read_intra_function_calls(struct objtool_file *file) +{ + struct instruction *insn; + struct section *sec; + struct rela *rela; + + sec = find_section_by_name(file->elf, ".rela.discard.intra_function_calls"); + if (!sec) + return 0; + + list_for_each_entry(rela, &sec->rela_list, list) { + unsigned long dest_off; + + if (rela->sym->type != STT_SECTION) { + WARN("unexpected relocation symbol type in %s", + sec->name); + return -1; + } + + insn = find_insn(file, rela->sym->sec, rela->addend); + if (!insn) { + WARN("bad .discard.intra_function_call entry"); + return -1; + } + + if (insn->type != INSN_CALL) { + WARN_FUNC("intra_function_call not a direct call", + insn->sec, insn->offset); + return -1; + } + + insn->intra_function_call = true; + + dest_off = insn->offset + insn->len + insn->immediate; + insn->jump_dest = find_insn(file, insn->sec, dest_off); + if (!insn->jump_dest) { + WARN_FUNC("can't find call dest at %s+0x%lx", + insn->sec, insn->offset, + insn->sec->name, dest_off); + return -1; + } + } + + return 0; +} + static void mark_rodata(struct objtool_file *file) { struct section *sec; @@ -1469,6 +1522,10 @@ static int decode_sections(struct objtoo if (ret) return ret; + ret = read_intra_function_calls(file); + if (ret) + return ret; + ret = add_call_destinations(file); if (ret) return ret; @@ -2260,7 +2317,8 @@ static int validate_branch(struct objtoo return ret; if (!no_fp && func && !is_fentry_call(insn) && - !has_valid_stack_frame(&state)) { + !has_valid_stack_frame(&state) && + !insn->intra_function_call) { WARN_FUNC("call without frame pointer save/setup", sec, insn->offset); return 1; @@ -2269,6 +2327,29 @@ static int validate_branch(struct objtoo if (dead_end_function(file, insn->call_dest)) return 0; + if (insn->intra_function_call) { + /* + * The call instruction can update the stack + * state. Then make the intra-function call + * behaves like and unconditional jump. + */ + ret = handle_insn_ops(insn, &state); + if (ret) + return ret; + + ret = validate_branch(file, func, insn, + insn->jump_dest, state); + if (ret) { + if (backtrace) { + BT_FUNC("(intra-function call)", + insn); + } + return ret; + } + + return 0; + } + break; case INSN_JUMP_CONDITIONAL: --- a/tools/objtool/check.h +++ b/tools/objtool/check.h @@ -33,6 +33,7 @@ struct instruction { int alt_group; bool dead_end, ignore, ignore_alts; bool hint; + bool intra_function_call; bool retpoline_safe; s8 instr; u8 visited;
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