The orc_sort_cmp() function, used with qsort(), previously violated the symmetry and transitivity rules required by the C standard. Specifically, when both entries are ORC_REG_UNDEFINED, it could result in both a < b and b < a, which breaks the required symmetry and transitivity. This can lead to undefined behavior and incorrect sorting results, potentially causing memory corruption in glibc implementations [1].
Symmetry: If x < y, then y > x. Transitivity: If x < y and y < z, then x < z.
Fix the comparison logic to return 0 when both entries are ORC_REG_UNDEFINED, ensuring compliance with qsort() requirements.
Link: https://www.qualys.com/2024/01/30/qsort.txt [1] Link: https://lkml.kernel.org/r/20241226140332.2670689-1-visitorckw@gmail.com Fixes: 57fa18994285 ("scripts/sorttable: Implement build-time ORC unwind table sorting") Fixes: fb799447ae29 ("x86,objtool: Split UNWIND_HINT_EMPTY in two") Signed-off-by: Kuan-Wei Chiu visitorckw@gmail.com Cc: Ching-Chun (Jim) Huang jserv@ccns.ncku.edu.tw Cc: chuang@cs.nycu.edu.tw Cc: Ingo Molnar mingo@kernel.org Cc: Josh Poimboeuf jpoimboe@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Shile Zhang shile.zhang@linux.alibaba.com Cc: Steven Rostedt rostedt@goodmis.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit 0210d251162f4033350a94a43f95b1c39ec84a90) Signed-off-by: Kuan-Wei Chiu visitorckw@gmail.com --- scripts/sorttable.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/scripts/sorttable.h b/scripts/sorttable.h index a2baa2fefb13..9013b6984d68 100644 --- a/scripts/sorttable.h +++ b/scripts/sorttable.h @@ -103,7 +103,7 @@ static inline unsigned long orc_ip(const int *ip)
static int orc_sort_cmp(const void *_a, const void *_b) { - struct orc_entry *orc_a; + struct orc_entry *orc_a, *orc_b; const int *a = g_orc_ip_table + *(int *)_a; const int *b = g_orc_ip_table + *(int *)_b; unsigned long a_val = orc_ip(a); @@ -121,6 +121,10 @@ static int orc_sort_cmp(const void *_a, const void *_b) * whitelisted .o files which didn't get objtool generation. */ orc_a = g_orc_table + (a - g_orc_ip_table); + orc_b = g_orc_table + (b - g_orc_ip_table); + if (orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end && + orc_b->sp_reg == ORC_REG_UNDEFINED && !orc_b->end) + return 0; return orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end ? -1 : 1; }