objtool: Fixes in .cold detection logic

PATCH New Josh Poimboeuf 2 participants 5 messages Nov 20, 2018 objtool

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Josh Poimboeuf

author

2018-11-20 17:53 UTC #0 lore raw

cover objtool: Fixes in .cold detection logic

A couple of objtool fixes from Artem Savkov. Fix a double-free in an error path, and a seg fault seen with -ffunction-sections.

Artem Savkov (2):
objtool: Fix double-free in .cold detection error path
objtool: Fix seg fault in .cold detection with -ffunction-sections

 tools/objtool/elf.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

Signature · 1 line

2.17.2

Josh Poimboeuf

author

2018-11-20 17:53 UTC #1 lore raw

PATCH 1/2 objtool: Fix double-free in .cold detection error path

From: Artem Savkov <[email protected]>

If read_symbols() fails during second list traversal (the one dealing with ".cold" subfunctions) it frees the symbol, but never deletes it from the list/hash_table resulting in symbol being freed again in elf_close(). Fix it by just returning an error, leaving cleanup to elf_close().

Fixes 13810435b9a7 ("objtool: Support GCC 8's cold subfunctions")

Signed-off-by Artem Savkov <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

---
 tools/objtool/elf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

tools/objtool/elf.c +1 -1

index 6dbb9fae0f9d..e7a7ac40e045 100644
@@ -312,7 +312,7 @@ static int read_symbols(struct elf *elf)
 			if (!pfunc) {
 				WARN("%s(): can't find parent function",
 				     sym->name);
-				goto err;
+				return -1;
 			}
 
 			sym->pfunc = pfunc;

Signature · 1 line

2.17.2

tip-bot for Artem Savkov

merge bot

2018-11-20 18:05 UTC #2 lore raw

[tip:core/urgent] objtool: Fix double-free in .cold detection error path

objtool: Fix double-free in .cold detection error path

Commit-ID:  0b9301fb632f7111a3293a30cc5b20f1b82ed08d
Gitweb:     https://git.kernel.org/tip/0b9301fb632f7111a3293a30cc5b20f1b82ed08d
Author:     Artem Savkov <[email protected]>
AuthorDate: Tue, 20 Nov 2018 11:52:15 -0600
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 20 Nov 2018 18:59:00 +0100

objtool: Fix double-free in .cold detection error path

Signed-off-by Artem Savkov <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Cc Linus Torvalds <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Thomas Gleixner <[email protected]>

Fixes 13810435b9a7 ("objtool: Support GCC 8's cold subfunctions")

Link http://lkml.kernel.org/r/beac5a9b7da9e8be90223459dcbe07766ae437dd.1542736240.git.jpoimboe@redhat.com open here

Signed-off-by Ingo Molnar <[email protected]>

---
 tools/objtool/elf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

tools/objtool/elf.c +1 -1

index 6dbb9fae0f9d..e7a7ac40e045 100644
@@ -312,7 +312,7 @@ static int read_symbols(struct elf *elf)
 			if (!pfunc) {
 				WARN("%s(): can't find parent function",
 				     sym->name);
-				goto err;
+				return -1;
 			}
 
 			sym->pfunc = pfunc;

Josh Poimboeuf

author

2018-11-20 17:53 UTC #3 lore raw

PATCH 2/2 objtool: Fix seg fault in .cold detection with -ffunction-sections

In reply to Josh Poimboeuf

From: Artem Savkov <[email protected]>

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.

Fixes 13810435b9a7 ("objtool: Support GCC 8's cold subfunctions")

Signed-off-by Artem Savkov <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

---
 tools/objtool/elf.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

tools/objtool/elf.c +14 -3

index e7a7ac40e045..b8f3cca8e58b 100644
@@ -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",

Signature · 1 line

2.17.2

tip-bot for Artem Savkov

merge bot

2018-11-20 18:06 UTC #4 lore raw

[tip:core/urgent] objtool: Fix segfault in .cold detection with -ffunction-sections

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

Commit-ID:  22566c1603030f0a036ad564634b064ad1a55db2
Gitweb:     https://git.kernel.org/tip/22566c1603030f0a036ad564634b064ad1a55db2
Author:     Artem Savkov <[email protected]>
AuthorDate: Tue, 20 Nov 2018 11:52:16 -0600
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 20 Nov 2018 18:59:00 +0100

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

Fix by copying the search string instead of modifying it in place.

Signed-off-by Artem Savkov <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Cc Linus Torvalds <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Thomas Gleixner <[email protected]>

Fixes 13810435b9a7 ("objtool: Support GCC 8's cold subfunctions")

Link http://lkml.kernel.org/r/910abd6b5a4945130fd44f787c24e07b9e07c8da.1542736240.git.jpoimboe@redhat.com open here

Signed-off-by Ingo Molnar <[email protected]>

---
 tools/objtool/elf.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

tools/objtool/elf.c +14 -3

index e7a7ac40e045..b8f3cca8e58b 100644
@@ -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",