On Wed, 11 Oct 2023 20:50:56 -0700
Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> The DWARF location expression can be fairly complex and it'd be hard
> to match it with the condition correctly. So let's be conservative
> and only allow simple expressions. For now it just checks the first
> operation in the list. The following operations looks ok:
>
> * DW_OP_stack_value
> * DW_OP_deref_size
> * DW_OP_deref
> * DW_OP_piece
>
> To refuse complex (and unsupported) location expressions, add
> check_allowed_ops() to compare the rest of the list. It seems earlier
> result contained those unsupported expressions. For example, I found
> some local struct variable is placed like below.
>
> <2><43d1517>: Abbrev Number: 62 (DW_TAG_variable)
> <43d1518> DW_AT_location : 15 byte block: 91 50 93 8 91 78 93 4 93 84 8 91 68 93 4
> (DW_OP_fbreg: -48; DW_OP_piece: 8;
> DW_OP_fbreg: -8; DW_OP_piece: 4;
> DW_OP_piece: 1028;
> DW_OP_fbreg: -24; DW_OP_piece: 4)
>
> Another example is something like this.
>
> 0057c8be ffffffffffffffff ffffffff812109f0 (base address)
> 0057c8ce ffffffff812112b5 ffffffff812112c8 (DW_OP_breg3 (rbx): 0;
> DW_OP_constu: 18446744073709551612;
> DW_OP_and;
> DW_OP_stack_value)
>
> It should refuse them. After the change, the stat shows:
>
> Annotate data type stats:
> total 294, ok 158 (53.7%), bad 136 (46.3%)
> -----------------------------------------------------------
> 30 : no_sym
> 32 : no_mem_ops
> 53 : no_var
> 14 : no_typeinfo
> 7 : bad_offset
>
The code itself looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
If this fixes the previous patch in the same series (this seems a fix for the
main usecase), please make it to a single patch.
Thank you,
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> ---
> tools/perf/util/dwarf-aux.c | 44 +++++++++++++++++++++++++++++++++----
> 1 file changed, 40 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 7f3822d08ab7..093d7e82b333 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -1305,6 +1305,34 @@ static bool match_var_offset(Dwarf_Die *die_mem, struct find_var_data *data,
> return true;
> }
>
> +static bool check_allowed_ops(Dwarf_Op *ops, size_t nops)
> +{
> + /* The first op is checked separately */
> + ops++;
> + nops--;
> +
> + /*
> + * It needs to make sure if the location expression matches to the given
> + * register and offset exactly. Thus it rejects any complex expressions
> + * and only allows a few of selected operators that doesn't change the
> + * location.
> + */
> + while (nops) {
> + switch (ops->atom) {
> + case DW_OP_stack_value:
> + case DW_OP_deref_size:
> + case DW_OP_deref:
> + case DW_OP_piece:
> + break;
> + default:
> + return false;
> + }
> + ops++;
> + nops--;
> + }
> + return true;
> +}
> +
> /* Only checks direct child DIEs in the given scope. */
> static int __die_find_var_reg_cb(Dwarf_Die *die_mem, void *arg)
> {
> @@ -1332,25 +1360,31 @@ static int __die_find_var_reg_cb(Dwarf_Die *die_mem, void *arg)
> /* Local variables accessed using frame base register */
> if (data->is_fbreg && ops->atom == DW_OP_fbreg &&
> data->offset >= (int)ops->number &&
> + check_allowed_ops(ops, nops) &&
> match_var_offset(die_mem, data, data->offset, ops->number))
> return DIE_FIND_CB_END;
>
> /* Only match with a simple case */
> if (data->reg < DWARF_OP_DIRECT_REGS) {
> - if (ops->atom == (DW_OP_reg0 + data->reg) && nops == 1)
> + /* pointer variables saved in a register 0 to 31 */
> + if (ops->atom == (DW_OP_reg0 + data->reg) &&
> + check_allowed_ops(ops, nops))
> return DIE_FIND_CB_END;
>
> /* Local variables accessed by a register + offset */
> if (ops->atom == (DW_OP_breg0 + data->reg) &&
> + check_allowed_ops(ops, nops) &&
> match_var_offset(die_mem, data, data->offset, ops->number))
> return DIE_FIND_CB_END;
> } else {
> + /* pointer variables saved in a register 32 or above */
> if (ops->atom == DW_OP_regx && ops->number == data->reg &&
> - nops == 1)
> + check_allowed_ops(ops, nops))
> return DIE_FIND_CB_END;
>
> /* Local variables accessed by a register + offset */
> if (ops->atom == DW_OP_bregx && data->reg == ops->number &&
> + check_allowed_ops(ops, nops) &&
> match_var_offset(die_mem, data, data->offset, ops->number2))
> return DIE_FIND_CB_END;
> }
> @@ -1412,7 +1446,8 @@ static int __die_find_var_addr_cb(Dwarf_Die *die_mem, void *arg)
> if (data->addr < ops->number)
> continue;
>
> - if (match_var_offset(die_mem, data, data->addr, ops->number))
> + if (check_allowed_ops(ops, nops) &&
> + match_var_offset(die_mem, data, data->addr, ops->number))
> return DIE_FIND_CB_END;
> }
> return DIE_FIND_CB_SIBLING;
> @@ -1501,7 +1536,8 @@ int die_get_cfa(Dwarf *dwarf, u64 pc, int *preg, int *poffset)
> return -1;
>
> if (!dwarf_cfi_addrframe(cfi, pc, &frame) &&
> - !dwarf_frame_cfa(frame, &ops, &nops) && nops == 1) {
> + !dwarf_frame_cfa(frame, &ops, &nops) &&
> + check_allowed_ops(ops, nops)) {
> *preg = reg_from_dwarf_op(ops);
> *poffset = offset_from_dwarf_op(ops);
> return 0;
> --
> 2.42.0.655.g421f12c284-goog
>
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
|