Messages in this thread Patch in this message | | | Date | Thu, 23 Apr 2020 13:40:56 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 4/7] objtool: Add support for intra-function calls |
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On Sun, Apr 19, 2020 at 11:41:50AM -0500, Josh Poimboeuf wrote:
> Could this be cleaner if the insn->type were just changed to > INSN_JUMP_UNCONDITIONAL? Then it could share the normal jump logic.
A little something like so, then?
--- Subject: objtool: Add support for intra-function calls From: Alexandre Chartre <alexandre.chartre@oracle.com> Date: Tue, 14 Apr 2020 12:36:12 +0200
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 | 8 ++ tools/objtool/check.c | 83 +++++++++++++++++++++-- 4 files changed, 103 insertions(+), 7 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 a 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 @@ -316,6 +316,14 @@ they mean, and suggestions for how to fi sources). +10. 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 @@ -516,6 +516,14 @@ 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). + */ + ADD_OP(op) { + op->src.type = OP_SRC_CONST; + op->dest.type = OP_DEST_PUSH; + } break; case 0xfc: --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -690,6 +690,16 @@ static int add_jump_destinations(struct return 0; } +static void remove_insn_ops(struct instruction *insn) +{ + struct stack_op *op, *tmp; + + list_for_each_entry_safe(op, tmp, &insn->stack_ops, list) { + list_del(&op->list); + free(op); + } +} + static bool setup_call_dest(struct objtool_file *file, struct instruction *insn) { unsigned long dest_off; @@ -700,19 +710,23 @@ static bool setup_call_dest(struct objto insn->call_dest = find_symbol_by_offset(insn->sec, dest_off); 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."); + WARN_FUNC("intra-function call", insn->sec, insn->offset); return false; } + /* regular call */ if (insn->func && insn->call_dest->type != STT_FUNC) { WARN_FUNC("unsupported call to non-function", insn->sec, insn->offset); return false; } + /* + * Whatever stack impact regular CALLs have, should be + * undone by the RETURN of the called function. + */ + remove_insn_ops(insn); + return true; } @@ -1423,6 +1437,57 @@ 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; + } + + /* + * Treat intra-function CALLs as JMPs, but with a stack_op. + * Also see how setup_call_dest() strips stack_ops from normal + * CALLs. + */ + insn->type = INSN_JUMP_UNCONDITIONAL; + + 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; @@ -1478,6 +1543,10 @@ 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; @@ -2252,6 +2321,9 @@ static int validate_branch(struct objtoo return 0; } + if (handle_insn_ops(insn, &state)) + return 1; + switch (insn->type) { case INSN_RETURN: @@ -2311,9 +2383,6 @@ static int validate_branch(struct objtoo break; case INSN_EXCEPTION_RETURN: - if (handle_insn_ops(insn, &state)) - return 1; - /* * This handles x86's sync_core() case, where we use an * IRET to self. All 'normal' IRET instructions are in
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