CVE-2024-26645

In the Linux kernel, the following vulnerability has been resolved:
tracing: Ensure visibility when inserting an element into tracing_map
Running the following two commands in parallel on a multi-processor AArch64
machine can sporadically produce an unexpected warning about duplicate
histogram entries: $ while true; do echo hist:key=id.syscall:val=hitcount >
\ /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger cat
/sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist sleep 0.001
done $ stress-ng --sysbadaddr $(nproc) The warning looks as follows: [
2911.172474] ------------[ cut here ]------------ [ 2911.173111] Duplicates
detected: 1 [ 2911.173574] WARNING: CPU: 2 PID: 12247 at
kernel/trace/tracing_map.c:983 tracing_map_sort_entries+0x3e0/0x408 [
2911.174702] Modules linked in: iscsi_ibft(E) iscsi_boot_sysfs(E) rfkill(E)
af_packet(E) nls_iso8859_1(E) nls_cp437(E) vfat(E) fat(E) ena(E)
tiny_power_button(E) qemu_fw_cfg(E) button(E) fuse(E) efi_pstore(E)
ip_tables(E) x_tables(E) xfs(E) libcrc32c(E) aes_ce_blk(E) aes_ce_cipher(E)
crct10dif_ce(E) polyval_ce(E) polyval_generic(E) ghash_ce(E) gf128mul(E)
sm4_ce_gcm(E) sm4_ce_ccm(E) sm4_ce(E) sm4_ce_cipher(E) sm4(E) sm3_ce(E)
sm3(E) sha3_ce(E) sha512_ce(E) sha512_arm64(E) sha2_ce(E) sha256_arm64(E)
nvme(E) sha1_ce(E) nvme_core(E) nvme_auth(E) t10_pi(E) sg(E) scsi_mod(E)
scsi_common(E) efivarfs(E) [ 2911.174738] Unloaded tainted modules:
cppc_cpufreq(E):1 [ 2911.180985] CPU: 2 PID: 12247 Comm: cat Kdump: loaded
Tainted: G E 6.7.0-default #2 1b58bbb22c97e4399dc09f92d309344f69c44a01 [
2911.182398] Hardware name: Amazon EC2 c7g.8xlarge/, BIOS 1.0 11/1/2018 [
2911.183208] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS
BTYPE=–) [ 2911.184038] pc : tracing_map_sort_entries+0x3e0/0x408 [
2911.184667] lr : tracing_map_sort_entries+0x3e0/0x408 [ 2911.185310] sp :
ffff8000a1513900 [ 2911.185750] x29: ffff8000a1513900 x28: ffff0003f272fe80
x27: 0000000000000001 [ 2911.186600] x26: ffff0003f272fe80 x25:
0000000000000030 x24: 0000000000000008 [ 2911.187458] x23: ffff0003c5788000
x22: ffff0003c16710c8 x21: ffff80008017f180 [ 2911.188310] x20:
ffff80008017f000 x19: ffff80008017f180 x18: ffffffffffffffff [ 2911.189160]
x17: 0000000000000000 x16: 0000000000000000 x15: ffff8000a15134b8 [
2911.190015] x14: 0000000000000000 x13: 205d373432323154 x12:
5b5d313131333731 [ 2911.190844] x11: 00000000fffeffff x10: 00000000fffeffff
x9 : ffffd1b78274a13c [ 2911.191716] x8 : 000000000017ffe8 x7 :
c0000000fffeffff x6 : 000000000057ffa8 [ 2911.192554] x5 : ffff0012f6c24ec0
x4 : 0000000000000000 x3 : ffff2e5b72b5d000 [ 2911.193404] x2 :
0000000000000000 x1 : 0000000000000000 x0 : ffff0003ff254480 [ 2911.194259]
Call trace: [ 2911.194626] tracing_map_sort_entries+0x3e0/0x408 [
2911.195220] hist_show+0x124/0x800 [ 2911.195692] seq_read_iter+0x1d4/0x4e8
[ 2911.196193] seq_read+0xe8/0x138 [ 2911.196638] vfs_read+0xc8/0x300 [
2911.197078] ksys_read+0x70/0x108 [ 2911.197534] __arm64_sys_read+0x24/0x38
[ 2911.198046] invoke_syscall+0x78/0x108 [ 2911.198553]
el0_svc_common.constprop.0+0xd0/0xf8 [ 2911.199157] do_el0_svc+0x28/0x40 [
2911.199613] el0_svc+0x40/0x178 [ 2911.200048]
el0t_64_sync_handler+0x13c/0x158 [ 2911.200621] el0t_64_sync+0x1a8/0x1b0 [
2911.201115] —[ end trace 0000000000000000 ]— The problem appears to be
caused by CPU reordering of writes issued from __tracing_map_insert(). The
check for the presence of an element with a given key in this function is:
val = READ_ONCE(entry->val); if (val && keys_match(key, val->key,
map->key_size)) … The write of a new entry is: elt = get_free_elt(map);
memcpy(elt->key, key, map->key_size); entry->val = elt; The
“memcpy(elt->key, key, map->key_size);” and “entry->val = elt;” stores may
become visible in the reversed order on another CPU. This second CPU might
then incorrectly determine that a new key doesn’t match an already present
val->key and subse —truncated—

Notes