From a8abb0c3dc1e28454851a00f8b7333d9695d566c Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Wed, 9 Feb 2022 12:33:23 +0530 Subject: bpf: Fix crash due to incorrect copy_map_value When both bpf_spin_lock and bpf_timer are present in a BPF map value, copy_map_value needs to skirt both objects when copying a value into and out of the map. However, the current code does not set both s_off and t_off in copy_map_value, which leads to a crash when e.g. bpf_spin_lock is placed in map value with bpf_timer, as bpf_map_update_elem call will be able to overwrite the other timer object. When the issue is not fixed, an overwriting can produce the following splat: [root@(none) bpf]# ./test_progs -t timer_crash [ 15.930339] bpf_testmod: loading out-of-tree module taints kernel. [ 16.037849] ================================================================== [ 16.038458] BUG: KASAN: user-memory-access in __pv_queued_spin_lock_slowpath+0x32b/0x520 [ 16.038944] Write of size 8 at addr 0000000000043ec0 by task test_progs/325 [ 16.039399] [ 16.039514] CPU: 0 PID: 325 Comm: test_progs Tainted: G OE 5.16.0+ #278 [ 16.039983] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ArchLinux 1.15.0-1 04/01/2014 [ 16.040485] Call Trace: [ 16.040645] [ 16.040805] dump_stack_lvl+0x59/0x73 [ 16.041069] ? __pv_queued_spin_lock_slowpath+0x32b/0x520 [ 16.041427] kasan_report.cold+0x116/0x11b [ 16.041673] ? __pv_queued_spin_lock_slowpath+0x32b/0x520 [ 16.042040] __pv_queued_spin_lock_slowpath+0x32b/0x520 [ 16.042328] ? memcpy+0x39/0x60 [ 16.042552] ? pv_hash+0xd0/0xd0 [ 16.042785] ? lockdep_hardirqs_off+0x95/0xd0 [ 16.043079] __bpf_spin_lock_irqsave+0xdf/0xf0 [ 16.043366] ? bpf_get_current_comm+0x50/0x50 [ 16.043608] ? jhash+0x11a/0x270 [ 16.043848] bpf_timer_cancel+0x34/0xe0 [ 16.044119] bpf_prog_c4ea1c0f7449940d_sys_enter+0x7c/0x81 [ 16.044500] bpf_trampoline_6442477838_0+0x36/0x1000 [ 16.044836] __x64_sys_nanosleep+0x5/0x140 [ 16.045119] do_syscall_64+0x59/0x80 [ 16.045377] ? lock_is_held_type+0xe4/0x140 [ 16.045670] ? irqentry_exit_to_user_mode+0xa/0x40 [ 16.046001] ? mark_held_locks+0x24/0x90 [ 16.046287] ? asm_exc_page_fault+0x1e/0x30 [ 16.046569] ? asm_exc_page_fault+0x8/0x30 [ 16.046851] ? lockdep_hardirqs_on+0x7e/0x100 [ 16.047137] entry_SYSCALL_64_after_hwframe+0x44/0xae [ 16.047405] RIP: 0033:0x7f9e4831718d [ 16.047602] Code: b4 0c 00 0f 05 eb a9 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d b3 6c 0c 00 f7 d8 64 89 01 48 [ 16.048764] RSP: 002b:00007fff488086b8 EFLAGS: 00000206 ORIG_RAX: 0000000000000023 [ 16.049275] RAX: ffffffffffffffda RBX: 00007f9e48683740 RCX: 00007f9e4831718d [ 16.049747] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007fff488086d0 [ 16.050225] RBP: 00007fff488086f0 R08: 00007fff488085d7 R09: 00007f9e4cb594a0 [ 16.050648] R10: 0000000000000000 R11: 0000000000000206 R12: 00007f9e484cde30 [ 16.051124] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 [ 16.051608] [ 16.051762] ================================================================== Fixes: 68134668c17f ("bpf: Add map side support for bpf timers.") Signed-off-by: Kumar Kartikeya Dwivedi Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20220209070324.1093182-2-memxor@gmail.com --- include/linux/bpf.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index fa517ae604ad..31a83449808b 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -224,7 +224,8 @@ static inline void copy_map_value(struct bpf_map *map, void *dst, void *src) if (unlikely(map_value_has_spin_lock(map))) { s_off = map->spin_lock_off; s_sz = sizeof(struct bpf_spin_lock); - } else if (unlikely(map_value_has_timer(map))) { + } + if (unlikely(map_value_has_timer(map))) { t_off = map->timer_off; t_sz = sizeof(struct bpf_timer); } -- cgit v1.2.3 From 5eaed6eedbe9612f642ad2b880f961d1c6c8ec2b Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Fri, 11 Feb 2022 11:49:53 -0800 Subject: bpf: Fix a bpf_timer initialization issue MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch in [1] intends to fix a bpf_timer related issue, but the fix caused existing 'timer' selftest to fail with hang or some random errors. After some debug, I found an issue with check_and_init_map_value() in the hashtab.c. More specifically, in hashtab.c, we have code l_new = bpf_map_kmalloc_node(&htab->map, ...) check_and_init_map_value(&htab->map, l_new...) Note that bpf_map_kmalloc_node() does not do initialization so l_new contains random value. The function check_and_init_map_value() intends to zero the bpf_spin_lock and bpf_timer if they exist in the map. But I found bpf_spin_lock is zero'ed but bpf_timer is not zero'ed. With [1], later copy_map_value() skips copying of bpf_spin_lock and bpf_timer. The non-zero bpf_timer caused random failures for 'timer' selftest. Without [1], for both bpf_spin_lock and bpf_timer case, bpf_timer will be zero'ed, so 'timer' self test is okay. For check_and_init_map_value(), why bpf_spin_lock is zero'ed properly while bpf_timer not. In bpf uapi header, we have struct bpf_spin_lock { __u32 val; }; struct bpf_timer { __u64 :64; __u64 :64; } __attribute__((aligned(8))); The initialization code: *(struct bpf_spin_lock *)(dst + map->spin_lock_off) = (struct bpf_spin_lock){}; *(struct bpf_timer *)(dst + map->timer_off) = (struct bpf_timer){}; It appears the compiler has no obligation to initialize anonymous fields. For example, let us use clang with bpf target as below: $ cat t.c struct bpf_timer { unsigned long long :64; }; struct bpf_timer2 { unsigned long long a; }; void test(struct bpf_timer *t) { *t = (struct bpf_timer){}; } void test2(struct bpf_timer2 *t) { *t = (struct bpf_timer2){}; } $ clang -target bpf -O2 -c -g t.c $ llvm-objdump -d t.o ... 0000000000000000 : 0: 95 00 00 00 00 00 00 00 exit 0000000000000008 : 1: b7 02 00 00 00 00 00 00 r2 = 0 2: 7b 21 00 00 00 00 00 00 *(u64 *)(r1 + 0) = r2 3: 95 00 00 00 00 00 00 00 exit gcc11.2 does not have the above issue. But from INTERNATIONAL STANDARD ©ISO/IEC ISO/IEC 9899:201x Programming languages — C http://www.open-std.org/Jtc1/sc22/wg14/www/docs/n1547.pdf page 157: Except where explicitly stated otherwise, for the purposes of this subclause unnamed members of objects of structure and union type do not participate in initialization. Unnamed members of structure objects have indeterminate value even after initialization. To fix the problem, let use memset for bpf_timer case in check_and_init_map_value(). For consistency, memset is also used for bpf_spin_lock case. [1] https://lore.kernel.org/bpf/20220209070324.1093182-2-memxor@gmail.com/ Fixes: 68134668c17f3 ("bpf: Add map side support for bpf timers.") Signed-off-by: Yonghong Song Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20220211194953.3142152-1-yhs@fb.com --- include/linux/bpf.h | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 31a83449808b..d0ad379d1e62 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -209,11 +209,9 @@ static inline bool map_value_has_timer(const struct bpf_map *map) static inline void check_and_init_map_value(struct bpf_map *map, void *dst) { if (unlikely(map_value_has_spin_lock(map))) - *(struct bpf_spin_lock *)(dst + map->spin_lock_off) = - (struct bpf_spin_lock){}; + memset(dst + map->spin_lock_off, 0, sizeof(struct bpf_spin_lock)); if (unlikely(map_value_has_timer(map))) - *(struct bpf_timer *)(dst + map->timer_off) = - (struct bpf_timer){}; + memset(dst + map->timer_off, 0, sizeof(struct bpf_timer)); } /* copy everything but bpf_spin_lock and bpf_timer. There could be one of each. */ -- cgit v1.2.3