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    Subject[PATCH V3 RESEND 2/3] objtool: Add support for intra-function calls
    Date
    From: Alexandre Chartre <alexandre.chartre@oracle.com>

    commit 8aa8eb2a8f5b3305a95f39957dd2b715fa668e21 upstream.

    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>
    Reviewed-by: Miroslav Benes <mbenes@suse.cz>
    Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Link: https://lkml.kernel.org/r/20200414103618.12657-4-alexandre.chartre@oracle.com
    Signed-off-by: Rui Qi <qirui.001@bytedance.com>
    ---
    include/linux/frame.h | 11 ++++
    .../Documentation/stack-validation.txt | 8 +++
    tools/objtool/arch/x86/decode.c | 6 ++
    tools/objtool/check.c | 62 +++++++++++++++++--
    4 files changed, 83 insertions(+), 4 deletions(-)

    diff --git a/include/linux/frame.h b/include/linux/frame.h
    index 02d3ca2d9598..303cda600e56 100644
    --- 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 */

    diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt
    index de094670050b..ee26bb382b70 100644
    --- 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 fix them.
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646


    +11. file.o: warning: unannotated 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.

    diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
    index a62e032863a8..c3ff62c085c8 100644
    --- a/tools/objtool/arch/x86/decode.c
    +++ b/tools/objtool/arch/x86/decode.c
    @@ -437,6 +437,12 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,

    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:
    diff --git a/tools/objtool/check.c b/tools/objtool/check.c
    index 71a24fd46dbd..0fa414869f45 100644
    --- a/tools/objtool/check.c
    +++ b/tools/objtool/check.c
    @@ -645,6 +645,7 @@ static int add_jump_destinations(struct objtool_file *file)
    return 0;
    }

    +
    /*
    * Find the destination instructions for all calls.
    */
    @@ -666,10 +667,7 @@ static int add_call_destinations(struct objtool_file *file)
    dest_off);

    if (!insn->call_dest && !insn->ignore) {
    - 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("unannotated intra-function call", insn->sec, insn->offset);
    return -1;
    }

    @@ -1291,6 +1289,58 @@ static int read_retpoline_hints(struct objtool_file *file)
    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.
    + * See add_call_destinations(), which 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;
    @@ -1346,6 +1396,10 @@ static int decode_sections(struct objtool_file *file)
    if (ret)
    return ret;

    + ret = read_intra_function_calls(file);
    + if (ret)
    + return ret;
    +
    ret = add_call_destinations(file);
    if (ret)
    return ret;
    --
    2.20.1

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