KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update (2)

syzbot syzbot 4 participants 6 messages Aug 29, 2023

Subsystems (2)

BPF BPF core

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author syzbot

2023-08-29 09:39 UTC #0 lore raw

Hello,

syzbot found the following issue on:

HEAD commit:    727dbda16b83 Merge tag 'hardening-v6.6-rc1' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136f39dfa80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dea9c2ce3f646a25
dashboard link: https://syzkaller.appspot.com/bug?extid=97522333291430dd277f
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9923a023ab11/disk-727dbda1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/650dbc695d77/vmlinux-727dbda1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/361da71276bf/bzImage-727dbda1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by [email protected]

==================================================================

BUG: KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update

write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:

 bpf_long_memcpy include/linux/bpf.h:428 [inline]
 bpf_obj_memcpy include/linux/bpf.h:441 [inline]
 copy_map_value_long include/linux/bpf.h:464 [inline]
 bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
 bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
 generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
 bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
 __sys_bpf+0x28a/0x780
 __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
 __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:

 bpf_long_memcpy include/linux/bpf.h:428 [inline]
 bpf_obj_memcpy include/linux/bpf.h:441 [inline]
 copy_map_value_long include/linux/bpf.h:464 [inline]
 bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
 bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
 generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
 bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
 __sys_bpf+0x28a/0x780
 __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
 __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x0000000000000000 -> 0xfffffff000002788

Reported by Kernel Concurrency Sanitizer on:

CPU: 0 PID: 8268 Comm: syz-executor.4 Not tainted 6.5.0-syzkaller-00453-g727dbda16b83 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
==================================================================

---
This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at [email protected].

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the bug is already fixed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite bug's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the bug is a duplicate of another bug, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Yonghong Song

reviewer

2023-08-29 18:30 UTC #1 lore raw

Quoted 56 lines · syzbot

Hello,

syzbot found the following issue on:

HEAD commit:    727dbda16b83 Merge tag 'hardening-v6.6-rc1' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136f39dfa80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dea9c2ce3f646a25
dashboard link: https://syzkaller.appspot.com/bug?extid=97522333291430dd277f
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by [email protected]

==================================================================

BUG: KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update

write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:

  bpf_long_memcpy include/linux/bpf.h:428 [inline]
  bpf_obj_memcpy include/linux/bpf.h:441 [inline]
  copy_map_value_long include/linux/bpf.h:464 [inline]
  bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
  bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
  generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
  bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
  __sys_bpf+0x28a/0x780
  __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
  __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
  __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:

  bpf_long_memcpy include/linux/bpf.h:428 [inline]
  bpf_obj_memcpy include/linux/bpf.h:441 [inline]
  copy_map_value_long include/linux/bpf.h:464 [inline]
  bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
  bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
  generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
  bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
  __sys_bpf+0x28a/0x780
  __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
  __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
  __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

Quoted 6 lines

value changed: 0x0000000000000000 -> 0xfffffff000002788

Reported by Kernel Concurrency Sanitizer on:

CPU: 0 PID: 8268 Comm: syz-executor.4 Not tainted 6.5.0-syzkaller-00453-g727dbda16b83 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
==================================================================

This case is with two tasks doing bpf_map batch update together for the same map and key.

Quoted 2 lines

write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:
write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:

So concurrency is introduced by user applications.
In my opinion, this probably not an issue from kernel perspective.

Quoted 23 lines

---
This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at [email protected].
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the bug is already fixed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite bug's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the bug is a duplicate of another bug, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup

Marco Elver

2023-08-29 18:54 UTC #2 lore raw

Quoted 67 lines · Yonghong Song

Quoted 56 lines · syzbot

Hello,

syzbot found the following issue on:

HEAD commit:    727dbda16b83 Merge tag 'hardening-v6.6-rc1' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136f39dfa80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dea9c2ce3f646a25
dashboard link: https://syzkaller.appspot.com/bug?extid=97522333291430dd277f
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by [email protected]

==================================================================

BUG: KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update

write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:

  bpf_long_memcpy include/linux/bpf.h:428 [inline]
  bpf_obj_memcpy include/linux/bpf.h:441 [inline]
  copy_map_value_long include/linux/bpf.h:464 [inline]
  bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
  bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
  generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
  bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
  __sys_bpf+0x28a/0x780
  __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
  __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
  __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:

  bpf_long_memcpy include/linux/bpf.h:428 [inline]
  bpf_obj_memcpy include/linux/bpf.h:441 [inline]
  copy_map_value_long include/linux/bpf.h:464 [inline]
  bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
  bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
  generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
  bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
  __sys_bpf+0x28a/0x780
  __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
  __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
  __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

Quoted 6 lines

value changed: 0x0000000000000000 -> 0xfffffff000002788

Reported by Kernel Concurrency Sanitizer on:

CPU: 0 PID: 8268 Comm: syz-executor.4 Not tainted 6.5.0-syzkaller-00453-g727dbda16b83 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
==================================================================

Quoted 7 lines

This case is with two tasks doing bpf_map batch update together for the same map and key.
Quoted 2 lines
write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:
write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:
So concurrency is introduced by user applications.
In my opinion, this probably not an issue from kernel perspective.

Perhaps not, but I recall there being a discussion about making KCSAN aware of memory accesses done by BPF programs (memcpy being a tiny subset of those). Not sure if the above data race qualifies as something we might want to still detect, i.e. a kernel dev testing their kernel might be interested in such a report.

Regardless, in this case we should teach syzkaller to ignore KCSAN data races that originate from bpf user operations whatever the origin.

Daniel Borkmann

maintainer

2023-08-29 20:04 UTC #3 lore raw

Quoted 79 lines · Marco Elver

Quoted 64 lines · Yonghong Song
Quoted 56 lines · syzbot
Hello,
syzbot found the following issue on:
HEAD commit:    727dbda16b83 Merge tag 'hardening-v6.6-rc1' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136f39dfa80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dea9c2ce3f646a25
dashboard link: https://syzkaller.appspot.com/bug?extid=97522333291430dd277f
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9923a023ab11/disk-727dbda1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/650dbc695d77/vmlinux-727dbda1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/361da71276bf/bzImage-727dbda1.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by [email protected]
==================================================================
BUG: KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update
write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:
   bpf_long_memcpy include/linux/bpf.h:428 [inline]
   bpf_obj_memcpy include/linux/bpf.h:441 [inline]
   copy_map_value_long include/linux/bpf.h:464 [inline]
   bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
   bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
   generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
   bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
   __sys_bpf+0x28a/0x780
   __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
   __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
   __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x63/0xcd
write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:
   bpf_long_memcpy include/linux/bpf.h:428 [inline]
   bpf_obj_memcpy include/linux/bpf.h:441 [inline]
   copy_map_value_long include/linux/bpf.h:464 [inline]
   bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
   bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
   generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
   bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
   __sys_bpf+0x28a/0x780
   __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
   __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
   __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x63/0xcd
Quoted 6 lines
value changed: 0x0000000000000000 -> 0xfffffff000002788
Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8268 Comm: syz-executor.4 Not tainted 6.5.0-syzkaller-00453-g727dbda16b83 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
==================================================================
Quoted 7 lines
This case is with two tasks doing bpf_map batch update together for the same map and key.
Quoted 2 lines
write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:
write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:
So concurrency is introduced by user applications.
In my opinion, this probably not an issue from kernel perspective.
Perhaps not, but I recall there being a discussion about making KCSAN aware of memory accesses done by BPF programs (memcpy being a tiny subset of those). Not sure if the above data race qualifies as something we might want to still detect, i.e. a kernel dev testing their kernel might be interested in such a report.

Quoted 3 lines

Regardless, in this case we should teach syzkaller to ignore KCSAN data races that originate from bpf user operations whatever the origin.

I presume KCSAN could be silenced here via READ_ONCE/WRITE_ONCE conversion?

include/linux/bpf.h +5 -2

index f58895830ada..32c4a37045f2 100644
@@ -424,8 +424,11 @@ static inline void bpf_long_memcpy(void *dst, const void *src, u32 size)
 	long *ldst = dst;
 
 	size /= sizeof(long);
-	while (size--)
-		*ldst++ = *lsrc++;
+	while (size--) {
+		WRITE_ONCE(*ldst, READ_ONCE(*lsrc));
+		ldst++;
+		lsrc++;
+	}
 }
 
 /* copy everything but bpf_spin_lock, bpf_timer, and kptrs. There could be one of each. */

Marco Elver

2023-08-29 20:37 UTC #4 lore raw

Quoted 92 lines · Daniel Borkmann

Quoted 79 lines · Marco Elver
Quoted 64 lines · Yonghong Song
Quoted 56 lines · syzbot
Hello,
syzbot found the following issue on:
HEAD commit:    727dbda16b83 Merge tag 'hardening-v6.6-rc1' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136f39dfa80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dea9c2ce3f646a25
dashboard link: https://syzkaller.appspot.com/bug?extid=97522333291430dd277f
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9923a023ab11/disk-727dbda1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/650dbc695d77/vmlinux-727dbda1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/361da71276bf/bzImage-727dbda1.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by [email protected]
==================================================================
BUG: KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update
write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:
   bpf_long_memcpy include/linux/bpf.h:428 [inline]
   bpf_obj_memcpy include/linux/bpf.h:441 [inline]
   copy_map_value_long include/linux/bpf.h:464 [inline]
   bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
   bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
   generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
   bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
   __sys_bpf+0x28a/0x780
   __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
   __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
   __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x63/0xcd
write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:
   bpf_long_memcpy include/linux/bpf.h:428 [inline]
   bpf_obj_memcpy include/linux/bpf.h:441 [inline]
   copy_map_value_long include/linux/bpf.h:464 [inline]
   bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380
   bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175
   generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749
   bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648
   __sys_bpf+0x28a/0x780
   __do_sys_bpf kernel/bpf/syscall.c:5241 [inline]
   __se_sys_bpf kernel/bpf/syscall.c:5239 [inline]
   __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x63/0xcd
Quoted 6 lines
value changed: 0x0000000000000000 -> 0xfffffff000002788
Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8268 Comm: syz-executor.4 Not tainted 6.5.0-syzkaller-00453-g727dbda16b83 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
==================================================================
Quoted 7 lines
This case is with two tasks doing bpf_map batch update together for the same map and key.
Quoted 2 lines
write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1:
write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:
So concurrency is introduced by user applications.
In my opinion, this probably not an issue from kernel perspective.
Perhaps not, but I recall there being a discussion about making KCSAN aware of memory accesses done by BPF programs (memcpy being a tiny subset of those). Not sure if the above data race qualifies as something we might want to still detect, i.e. a kernel dev testing their kernel might be interested in such a report.
Quoted 3 lines
Regardless, in this case we should teach syzkaller to ignore KCSAN data races that originate from bpf user operations whatever the origin.
I presume KCSAN could be silenced here via READ_ONCE/WRITE_ONCE conversion?
include/linux/bpf.h +0 -0
index f58895830ada..32c4a37045f2 100644

include/linux/bpf.h static inline void bpf_long_memcpy(void *dst, const void *src, u32 size) · line 431

Quoted 10 lines

include/linux/bpf.h +5 -2

@@ -424,8 +424,11 @@ static inline void bpf_long_memcpy(void *dst, const void *src, u32 size)
        long *ldst = dst;
 
        size /= sizeof(long);
-       while (size--)
-               *ldst++ = *lsrc++;
+       while (size--) {
+               WRITE_ONCE(*ldst, READ_ONCE(*lsrc));
+               ldst++;
+               lsrc++;
+       }

In this case, maybe data_race(*ldst++ = *lsrc++) would be more appropriate and efficient. Unlikely that READ_ONCE()/WRITE_ONCE() here helps make this any safer, i.e. the memcpy is still not atomic and if it's a bug on the user's side, it'll corrupt data either way.

Daniel Borkmann

maintainer

2023-08-29 20:55 UTC #5 lore raw

On 8/29/23 10:36 PM, Marco Elver wrote:
[...]

Quoted 4 lines

In this case, maybe data_race(*ldst++ = *lsrc++) would be more appropriate and efficient. Unlikely that READ_ONCE()/WRITE_ONCE() here helps make this any safer, i.e. the memcpy is still not atomic and if it's a bug on the user's side, it'll corrupt data either way.

I wasn't aware of data_race(), thanks for the suggestion! Just flushed out a small patch.

Thanks,
Daniel