Re: [PATCH v3 2/2] objtool: fix .cold functions parent symbols search

Josh Poimboeuf
2018-11-19T18:02:42Z

On Mon, Nov 12, 2018 at 01:55:19PM +0100, Artem Savkov wrote:
> Because find_symbol_by_name() traverses the same lists as read_symbols()
> changing sym->name in place without copying it affects the result of
> find_symbol_by_name() and, in case when ".cold" function precedes it's
> parent in sec->symbol_list, can result in function being considered a
> parent of itself. This leads to function length being set to 0 and other
> consequent side-effects including a segfault in add_switch_table().
> The effects of this bug are only visible when building with
> -ffunction-sections in KCFLAGS.
>
> Fix by copying the search string instead of modifying it in place.
>
> Fixes: 13810435b9a7 "objtool: Support GCC 8's cold subfunctions"

Same here, needs parentheses.

> Signed-off-by: Artem Savkov <asavkov@redhat.com>
> ---
> tools/objtool/elf.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
> index 3decd43477df..15d9acfb2c97 100644
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -31,6 +31,8 @@
> #include "elf.h"
> #include "warn.h"
>
> +#define MAX_NAME_LEN 128
> +
> struct section *find_section_by_name(struct elf *elf, const char *name)
> {
> struct section *sec;
> @@ -298,6 +300,8 @@ static int read_symbols(struct elf *elf)
> /* Create parent/child links for any cold subfunctions */
> list_for_each_entry(sec, &elf->sections, list) {
> list_for_each_entry(sym, &sec->symbol_list, list) {
> + char pname[MAX_NAME_LEN + 1];
> + size_t pnamelen;
> if (sym->type != STT_FUNC)
> continue;
> sym->pfunc = sym->cfunc = sym;
> @@ -305,9 +309,16 @@ static int read_symbols(struct elf *elf)
> if (!coldstr)
> continue;
>
> - coldstr[0] = '\0';
> - pfunc = find_symbol_by_name(elf, sym->name);
> - coldstr[0] = '.';
> + pnamelen = coldstr - sym->name;
> + if (pnamelen > MAX_NAME_LEN) {
> + WARN("%s(): parent function name exceeds maximum length of %d characters",
> + sym->name, MAX_NAME_LEN);
> + goto cold_err;

Same here, makes more sense to just return -1 and let elf_close() clean
it up I think.

--
Josh