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Subject[PATCH v4 2/2] objtool: fix .cold functions parent symbols search
Date
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")
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 e7a7ac40e045..b8f3cca8e58b 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);
+ return -1;
+ }
+
+ strncpy(pname, sym->name, pnamelen);
+ pname[pnamelen] = '\0';
+ pfunc = find_symbol_by_name(elf, pname);

if (!pfunc) {
WARN("%s(): can't find parent function",
--
2.19.1
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