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objtool: Fix segfault in .cold detection with -ffunction-sections 

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().  In the case where a ".cold"
function precedes its parent in sec->symbol_list, it can result in a
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.

Signed-off-by: Artem Savkov <asavkov@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 13810435b9 ("objtool: Support GCC 8's cold subfunctions")
Link: http://lkml.kernel.org/r/910abd6b5a4945130fd44f787c24e07b9e07c8da.1542736240.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Artem Savkov 2018-11-20 11:52:16 -06:00 committed by Ingo Molnar
parent 0b9301fb63
commit 22566c1603
1 changed files with 14 additions and 3 deletions
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17
tools/objtool/elf.c
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@ -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",