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Date: Sat, 29 Aug 2020 15:13:23 -0700
From: Yonghong Song <yhs@...com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>,
<davem@...emloft.net>
CC: <daniel@...earbox.net>, <josef@...icpanda.com>,
<bpoirier@...e.com>, <akpm@...ux-foundation.org>,
<hannes@...xchg.org>, <netdev@...r.kernel.org>,
<bpf@...r.kernel.org>, <kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next 5/5] selftests/bpf: Add sleepable tests
On 8/27/20 3:01 PM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@...nel.org>
>
> Modify few tests to sanity test sleepable bpf functionality.
>
> Running 'bench trig-fentry-sleep' vs 'bench trig-fentry' and 'perf report':
> sleepable with SRCU:
> 3.86% bench [k] __srcu_read_unlock
> 3.22% bench [k] __srcu_read_lock
> 0.92% bench [k] bpf_prog_740d4210cdcd99a3_bench_trigger_fentry_sleep
> 0.50% bench [k] bpf_trampoline_10297
> 0.26% bench [k] __bpf_prog_exit_sleepable
> 0.21% bench [k] __bpf_prog_enter_sleepable
>
> sleepable with RCU_TRACE:
> 0.79% bench [k] bpf_prog_740d4210cdcd99a3_bench_trigger_fentry_sleep
> 0.72% bench [k] bpf_trampoline_10381
> 0.31% bench [k] __bpf_prog_exit_sleepable
> 0.29% bench [k] __bpf_prog_enter_sleepable
>
> non-sleepable with RCU:
> 0.88% bench [k] bpf_prog_740d4210cdcd99a3_bench_trigger_fentry
> 0.84% bench [k] bpf_trampoline_10297
> 0.13% bench [k] __bpf_prog_enter
> 0.12% bench [k] __bpf_prog_exit
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> Acked-by: KP Singh <kpsingh@...gle.com>
> ---
> tools/testing/selftests/bpf/bench.c | 2 +
> .../selftests/bpf/benchs/bench_trigger.c | 17 +++++
> .../selftests/bpf/prog_tests/test_lsm.c | 9 +++
> tools/testing/selftests/bpf/progs/lsm.c | 66 ++++++++++++++++++-
> .../selftests/bpf/progs/trigger_bench.c | 7 ++
> 5 files changed, 99 insertions(+), 2 deletions(-)
>
[...]
> diff --git a/tools/testing/selftests/bpf/progs/lsm.c b/tools/testing/selftests/bpf/progs/lsm.c
> index b4598d4bc4f7..49fa6ca99755 100644
> --- a/tools/testing/selftests/bpf/progs/lsm.c
> +++ b/tools/testing/selftests/bpf/progs/lsm.c
> @@ -9,16 +9,41 @@
> #include <bpf/bpf_tracing.h>
> #include <errno.h>
>
> +struct {
> + __uint(type, BPF_MAP_TYPE_ARRAY);
> + __uint(max_entries, 1);
> + __type(key, __u32);
> + __type(value, __u64);
> +} array SEC(".maps");
> +
> +struct {
> + __uint(type, BPF_MAP_TYPE_HASH);
> + __uint(max_entries, 1);
> + __type(key, __u32);
> + __type(value, __u64);
> +} hash SEC(".maps");
> +
> +struct {
> + __uint(type, BPF_MAP_TYPE_LRU_HASH);
> + __uint(max_entries, 1);
> + __type(key, __u32);
> + __type(value, __u64);
> +} lru_hash SEC(".maps");
> +
> char _license[] SEC("license") = "GPL";
>
> int monitored_pid = 0;
> int mprotect_count = 0;
> int bprm_count = 0;
>
> -SEC("lsm/file_mprotect")
> +SEC("lsm.s/file_mprotect")
When running selftest, I hit the following kernel warning:
[ 250.871267] ============================================
[ 250.871902] WARNING: possible recursive locking detected
[ 250.872561] 5.9.0-rc1+ #830 Not tainted
[ 250.873166] --------------------------------------------
[ 250.873991] true/2053 is trying to acquire lock:
[ 250.874715] ffff8fc1f9cd2068 (&mm->mmap_lock#2){++++}-{3:3}, at:
__might_fault+0x3e/0x90
[ 250.875943]
[ 250.875943] but task is already holding lock:
[ 250.876688] ffff8fc1f9cd2068 (&mm->mmap_lock#2){++++}-{3:3}, at:
do_mprotect_pkey+0xb5/0x2f0
[ 250.877978]
[ 250.877978] other info that might help us debug this:
[ 250.878797] Possible unsafe locking scenario:
[ 250.878797]
[ 250.879708] CPU0
[ 250.880095] ----
[ 250.880482] lock(&mm->mmap_lock#2);
[ 250.881063] lock(&mm->mmap_lock#2);
[ 250.881645]
[ 250.881645] *** DEADLOCK ***
[ 250.881645]
[ 250.882559] May be due to missing lock nesting notation
[ 250.882559]
[ 250.883613] 2 locks held by true/2053:
[ 250.884194] #0: ffff8fc1f9cd2068 (&mm->mmap_lock#2){++++}-{3:3}, at:
do_mprotect_pkey+0xb5/0x2f0
[ 250.885558] #1: ffffffffbc47b8a0 (rcu_read_lock_trace){....}-{0:0},
at: __bpf_prog_enter_sleepable+0x0/0x40
[ 250.887062]
[ 250.887062] stack backtrace:
[ 250.887583] CPU: 1 PID: 2053 Comm: true Not tainted 5.9.0-rc1+ #830
[ 250.888546] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.9.3-1.el7.centos 04/01/2014
[ 250.889896] Call Trace:
[ 250.890222] dump_stack+0x78/0xa0
[ 250.890644] __lock_acquire.cold.74+0x209/0x2e3
[ 250.891350] lock_acquire+0xba/0x380
[ 250.891919] ? __might_fault+0x3e/0x90
[ 250.892510] ? __lock_acquire+0x639/0x20c0
[ 250.893150] __might_fault+0x68/0x90
[ 250.893717] ? __might_fault+0x3e/0x90
[ 250.894325] _copy_from_user+0x1e/0xa0
[ 250.894946] bpf_copy_from_user+0x22/0x50
[ 250.895581] bpf_prog_3717002769f30998_test_int_hook+0x76/0x60c
[ 250.896446] ? __bpf_prog_enter_sleepable+0x3c/0x40
[ 250.897207] ? __bpf_prog_exit+0xa0/0xa0
[ 250.897819] bpf_trampoline_18669+0x29/0x1000
[ 250.898476] bpf_lsm_file_mprotect+0x5/0x10
[ 250.899133] security_file_mprotect+0x32/0x50
[ 250.899816] do_mprotect_pkey+0x18a/0x2f0
[ 250.900472] __x64_sys_mprotect+0x1b/0x20
[ 250.901107] do_syscall_64+0x33/0x40
[ 250.901670] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 250.902450] RIP: 0033:0x7fd95c141ef7
[ 250.903014] Code: ff 66 90 b8 0b 00 00 00 0f 05 48 3d 01 f0 ff ff 73
01 c3 48 8d 0d 21 c2 2
0 00 f7 d8 89 01 48 83 c8 ff c3 b8 0a 00 00 00 0f 05 <48> 3d 01 f0 ff ff
73 01 c3 48 8d 0d 01
c2 20 00 f7 d8 89 01 48 83
[ 250.905732] RSP: 002b:00007ffd4c291fe8 EFLAGS: 00000246 ORIG_RAX:
000000000000000a
[ 250.906773] RAX: ffffffffffffffda RBX: 0000000000000005 RCX:
00007fd95c141ef7
[ 250.907866] RDX: 0000000000000000 RSI: 00000000001ff000 RDI:
00007fd95bf20000
[ 250.908906] RBP: 00007ffd4c292320 R08: 0000000000000000 R09:
0000000000000000
[ 250.909915] R10: 00007ffd4c291ff0 R11: 0000000000000246 R12:
00007fd95c341000
[ 250.910919] R13: 00007ffd4c292408 R14: 0000000000000002 R15:
0000000000000801
Could this be an real issue here?
do_mprotect_pkey() gets a lock of current->mm->mmap_lock
before calling security_file_mprotect(bpf_lsm_file_mprotect).
Later on, when do _copy_to_user(), page fault may happen
and current->mm->mmap_lock might be acquired again and may
have a deadlock here?
> int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
> unsigned long reqprot, unsigned long prot, int ret)
> {
> + char args[64];
> + __u32 key = 0;
> + __u64 *value;
> +
> if (ret != 0)
> return ret;
>
> @@ -28,6 +53,18 @@ int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
> is_stack = (vma->vm_start <= vma->vm_mm->start_stack &&
> vma->vm_end >= vma->vm_mm->start_stack);
>
> + bpf_copy_from_user(args, sizeof(args), (void *)vma->vm_mm->arg_start);
> +
> + value = bpf_map_lookup_elem(&array, &key);
> + if (value)
> + *value = 0;
> + value = bpf_map_lookup_elem(&hash, &key);
> + if (value)
> + *value = 0;
> + value = bpf_map_lookup_elem(&lru_hash, &key);
> + if (value)
> + *value = 0;
> +
> if (is_stack && monitored_pid == pid) {
> mprotect_count++;
> ret = -EPERM;
> @@ -36,7 +73,7 @@ int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
> return ret;
> }
>
[...]
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