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Date: Mon, 8 Nov 2021 19:55:30 +0300
From: Denis Kirjanov <dkirjanov@...e.de>
To: Dmitrii Banshchikov <me@...que.spb.ru>, bpf@...r.kernel.org
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
kafai@...com, songliubraving@...com, yhs@...com,
john.fastabend@...il.com, kpsingh@...nel.org,
netdev@...r.kernel.org, rdna@...com, john.stultz@...aro.org,
sboyd@...nel.org, peterz@...radead.org, mark.rutland@....com,
rosted@...dmis.org,
syzbot+43fd005b5a1b4d10781e@...kaller.appspotmail.com
Subject: Re: [PATCH bpf 1/2] bpf: Forbid bpf_ktime_get_coarse_ns and
bpf_timer_* in tracing progs
11/8/21 7:46 PM, Dmitrii Banshchikov пишет:
> bpf_ktime_get_coarse_ns() helper uses ktime_get_coarse_ns() time
> accessor that isn't safe for any context.
> This results in locking issues:
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.15.0-syzkaller #0 Not tainted
> ------------------------------------------------------
> syz-executor.4/14877 is trying to acquire lock:
> ffffffff8cb30008 (tk_core.seq.seqcount){----}-{0:0}, at: ktime_get_coarse_ts64+0x25/0x110 kernel/time/timekeeping.c:2255
>
> but task is already holding lock:
> ffffffff90dbf200 (&obj_hash[i].lock){-.-.}-{2:2}, at: debug_object_deactivate+0x61/0x400 lib/debugobjects.c:735
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&obj_hash[i].lock){-.-.}-{2:2}:
> lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5625
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0xd1/0x120 kernel/locking/spinlock.c:162
> __debug_object_init+0xd9/0x1860 lib/debugobjects.c:569
> debug_hrtimer_init kernel/time/hrtimer.c:414 [inline]
> debug_init kernel/time/hrtimer.c:468 [inline]
> hrtimer_init+0x20/0x40 kernel/time/hrtimer.c:1592
> ntp_init_cmos_sync kernel/time/ntp.c:676 [inline]
> ntp_init+0xa1/0xad kernel/time/ntp.c:1095
> timekeeping_init+0x512/0x6bf kernel/time/timekeeping.c:1639
> start_kernel+0x267/0x56e init/main.c:1030
> secondary_startup_64_no_verify+0xb1/0xbb
>
> -> #0 (tk_core.seq.seqcount){----}-{0:0}:
> check_prev_add kernel/locking/lockdep.c:3051 [inline]
> check_prevs_add kernel/locking/lockdep.c:3174 [inline]
> validate_chain+0x1dfb/0x8240 kernel/locking/lockdep.c:3789
> __lock_acquire+0x1382/0x2b00 kernel/locking/lockdep.c:5015
> lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5625
> seqcount_lockdep_reader_access+0xfe/0x230 include/linux/seqlock.h:103
> ktime_get_coarse_ts64+0x25/0x110 kernel/time/timekeeping.c:2255
> ktime_get_coarse include/linux/timekeeping.h:120 [inline]
> ktime_get_coarse_ns include/linux/timekeeping.h:126 [inline]
> ____bpf_ktime_get_coarse_ns kernel/bpf/helpers.c:173 [inline]
> bpf_ktime_get_coarse_ns+0x7e/0x130 kernel/bpf/helpers.c:171
> bpf_prog_a99735ebafdda2f1+0x10/0xb50
> bpf_dispatcher_nop_func include/linux/bpf.h:721 [inline]
> __bpf_prog_run include/linux/filter.h:626 [inline]
> bpf_prog_run include/linux/filter.h:633 [inline]
> BPF_PROG_RUN_ARRAY include/linux/bpf.h:1294 [inline]
> trace_call_bpf+0x2cf/0x5d0 kernel/trace/bpf_trace.c:127
> perf_trace_run_bpf_submit+0x7b/0x1d0 kernel/events/core.c:9708
> perf_trace_lock+0x37c/0x440 include/trace/events/lock.h:39
> trace_lock_release+0x128/0x150 include/trace/events/lock.h:58
> lock_release+0x82/0x810 kernel/locking/lockdep.c:5636
> __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:149 [inline]
> _raw_spin_unlock_irqrestore+0x75/0x130 kernel/locking/spinlock.c:194
> debug_hrtimer_deactivate kernel/time/hrtimer.c:425 [inline]
> debug_deactivate kernel/time/hrtimer.c:481 [inline]
> __run_hrtimer kernel/time/hrtimer.c:1653 [inline]
> __hrtimer_run_queues+0x2f9/0xa60 kernel/time/hrtimer.c:1749
> hrtimer_interrupt+0x3b3/0x1040 kernel/time/hrtimer.c:1811
> local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1086 [inline]
> __sysvec_apic_timer_interrupt+0xf9/0x270 arch/x86/kernel/apic/apic.c:1103
> sysvec_apic_timer_interrupt+0x8c/0xb0 arch/x86/kernel/apic/apic.c:1097
> asm_sysvec_apic_timer_interrupt+0x12/0x20
> __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
> _raw_spin_unlock_irqrestore+0xd4/0x130 kernel/locking/spinlock.c:194
> try_to_wake_up+0x702/0xd20 kernel/sched/core.c:4118
> wake_up_process kernel/sched/core.c:4200 [inline]
> wake_up_q+0x9a/0xf0 kernel/sched/core.c:953
> futex_wake+0x50f/0x5b0 kernel/futex/waitwake.c:184
> do_futex+0x367/0x560 kernel/futex/syscalls.c:127
> __do_sys_futex kernel/futex/syscalls.c:199 [inline]
> __se_sys_futex+0x401/0x4b0 kernel/futex/syscalls.c:180
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Locking issues are also possible with bpf_timer_* set of helpers:
>
> hrtimer_start()
> lock_base();
> trace_hrtimer...()
> perf_event()
> bpf_run()
> bpf_timer_start()
> hrtimer_start()
> lock_base() <- DEADLOCK
>
> Forbid use of bpf_ktime_get_coarse_ns() and bpf_timer_* helpers in
> BPF_PROG_TYPE_KPROBE, BPF_PROG_TYPE_TRACEPOINT, BPF_PROG_TYPE_PERF_EVENT
> and BPF_PROG_TYPE_RAW_TRACEPOINT prog types as it may result locking
> issues.
>
> Signed-off-by: Dmitrii Banshchikov <me@...que.spb.ru>
> Reported-by: syzbot+43fd005b5a1b4d10781e@...kaller.appspotmail.com
Add Fixes tag
> ---
> kernel/bpf/helpers.c | 30 ++++++++++++++++++++++++++++++
> 1 file changed, 30 insertions(+)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 1ffd469c217f..3de24928166e 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -18,6 +18,19 @@
>
> #include "../../lib/kstrtox.h"
>
> +static bool is_tracing_prog_type(enum bpf_prog_type type)
> +{
> + switch (type) {
> + case BPF_PROG_TYPE_KPROBE:
> + case BPF_PROG_TYPE_TRACEPOINT:
> + case BPF_PROG_TYPE_PERF_EVENT:
> + case BPF_PROG_TYPE_RAW_TRACEPOINT:
> + return true;
> + default:
> + return false;
> + }
> +}
> +
> /* If kernel subsystem is allowing eBPF programs to call this function,
> * inside its own verifier_ops->get_func_proto() callback it should return
> * bpf_map_lookup_elem_proto, so that verifier can properly check the arguments
> @@ -173,10 +186,18 @@ BPF_CALL_0(bpf_ktime_get_coarse_ns)
> return ktime_get_coarse_ns();
> }
>
> +static bool bpf_ktime_get_coarse_ns_allowed(const struct bpf_prog *prog)
> +{
> + // Forbid prog types that might be non-safe for non-fast variants of time accessors
The comments embaced with /* */
> +
> + return !is_tracing_prog_type(prog->type);
> +}
> +
> const struct bpf_func_proto bpf_ktime_get_coarse_ns_proto = {
> .func = bpf_ktime_get_coarse_ns,
> .gpl_only = false,
> .ret_type = RET_INTEGER,
> + .allowed = bpf_ktime_get_coarse_ns_allowed,
> };
>
> BPF_CALL_0(bpf_get_current_pid_tgid)
> @@ -1140,6 +1161,11 @@ BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map
> return ret;
> }
>
> +static bool bpf_timer_allowed(const struct bpf_prog *prog)
> +{
> + return !is_tracing_prog_type(prog->type);
> +}
> +
> static const struct bpf_func_proto bpf_timer_init_proto = {
> .func = bpf_timer_init,
> .gpl_only = true,
> @@ -1147,6 +1173,7 @@ static const struct bpf_func_proto bpf_timer_init_proto = {
> .arg1_type = ARG_PTR_TO_TIMER,
> .arg2_type = ARG_CONST_MAP_PTR,
> .arg3_type = ARG_ANYTHING,
> + .allowed = bpf_timer_allowed,
> };
>
> BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callback_fn,
> @@ -1200,6 +1227,7 @@ static const struct bpf_func_proto bpf_timer_set_callback_proto = {
> .ret_type = RET_INTEGER,
> .arg1_type = ARG_PTR_TO_TIMER,
> .arg2_type = ARG_PTR_TO_FUNC,
> + .allowed = bpf_timer_allowed,
> };
>
> BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, flags)
> @@ -1230,6 +1258,7 @@ static const struct bpf_func_proto bpf_timer_start_proto = {
> .arg1_type = ARG_PTR_TO_TIMER,
> .arg2_type = ARG_ANYTHING,
> .arg3_type = ARG_ANYTHING,
> + .allowed = bpf_timer_allowed,
> };
>
> static void drop_prog_refcnt(struct bpf_hrtimer *t)
> @@ -1279,6 +1308,7 @@ static const struct bpf_func_proto bpf_timer_cancel_proto = {
> .gpl_only = true,
> .ret_type = RET_INTEGER,
> .arg1_type = ARG_PTR_TO_TIMER,
> + .allowed = bpf_timer_allowed,
> };
>
> /* This function is called by map_delete/update_elem for individual element and
>
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