Commit 22566c16 authored Nov 20, 2018 by Artem Savkov Committed by Ingo Molnar Nov 20, 2018

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: 13810435 ("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>

parent 0b9301fb

tools/objtool/elf.c

+14 −3

Original line number	Diff line number	Diff line
		@@ -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",

Admin message