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    Subject[PATCH 5.13 074/223] bpf: Fix tail_call_reachable rejection for interpreter when jit failed
    Date
    From: Daniel Borkmann <daniel@iogearbox.net>

    [ Upstream commit 5dd0a6b8582ffbfa88351949d50eccd5b6694ade ]

    During testing of f263a81451c1 ("bpf: Track subprog poke descriptors correctly
    and fix use-after-free") under various failure conditions, for example, when
    jit_subprogs() fails and tries to clean up the program to be run under the
    interpreter, we ran into the following freeze:

    [...]
    #127/8 tailcall_bpf2bpf_3:FAIL
    [...]
    [ 92.041251] BUG: KASAN: slab-out-of-bounds in ___bpf_prog_run+0x1b9d/0x2e20
    [ 92.042408] Read of size 8 at addr ffff88800da67f68 by task test_progs/682
    [ 92.043707]
    [ 92.044030] CPU: 1 PID: 682 Comm: test_progs Tainted: G O 5.13.0-53301-ge6c08cb33a30-dirty #87
    [ 92.045542] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
    [ 92.046785] Call Trace:
    [ 92.047171] ? __bpf_prog_run_args64+0xc0/0xc0
    [ 92.047773] ? __bpf_prog_run_args32+0x8b/0xb0
    [ 92.048389] ? __bpf_prog_run_args64+0xc0/0xc0
    [ 92.049019] ? ktime_get+0x117/0x130
    [...] // few hundred [similar] lines more
    [ 92.659025] ? ktime_get+0x117/0x130
    [ 92.659845] ? __bpf_prog_run_args64+0xc0/0xc0
    [ 92.660738] ? __bpf_prog_run_args32+0x8b/0xb0
    [ 92.661528] ? __bpf_prog_run_args64+0xc0/0xc0
    [ 92.662378] ? print_usage_bug+0x50/0x50
    [ 92.663221] ? print_usage_bug+0x50/0x50
    [ 92.664077] ? bpf_ksym_find+0x9c/0xe0
    [ 92.664887] ? ktime_get+0x117/0x130
    [ 92.665624] ? kernel_text_address+0xf5/0x100
    [ 92.666529] ? __kernel_text_address+0xe/0x30
    [ 92.667725] ? unwind_get_return_address+0x2f/0x50
    [ 92.668854] ? ___bpf_prog_run+0x15d4/0x2e20
    [ 92.670185] ? ktime_get+0x117/0x130
    [ 92.671130] ? __bpf_prog_run_args64+0xc0/0xc0
    [ 92.672020] ? __bpf_prog_run_args32+0x8b/0xb0
    [ 92.672860] ? __bpf_prog_run_args64+0xc0/0xc0
    [ 92.675159] ? ktime_get+0x117/0x130
    [ 92.677074] ? lock_is_held_type+0xd5/0x130
    [ 92.678662] ? ___bpf_prog_run+0x15d4/0x2e20
    [ 92.680046] ? ktime_get+0x117/0x130
    [ 92.681285] ? __bpf_prog_run32+0x6b/0x90
    [ 92.682601] ? __bpf_prog_run64+0x90/0x90
    [ 92.683636] ? lock_downgrade+0x370/0x370
    [ 92.684647] ? mark_held_locks+0x44/0x90
    [ 92.685652] ? ktime_get+0x117/0x130
    [ 92.686752] ? lockdep_hardirqs_on+0x79/0x100
    [ 92.688004] ? ktime_get+0x117/0x130
    [ 92.688573] ? __cant_migrate+0x2b/0x80
    [ 92.689192] ? bpf_test_run+0x2f4/0x510
    [ 92.689869] ? bpf_test_timer_continue+0x1c0/0x1c0
    [ 92.690856] ? rcu_read_lock_bh_held+0x90/0x90
    [ 92.691506] ? __kasan_slab_alloc+0x61/0x80
    [ 92.692128] ? eth_type_trans+0x128/0x240
    [ 92.692737] ? __build_skb+0x46/0x50
    [ 92.693252] ? bpf_prog_test_run_skb+0x65e/0xc50
    [ 92.693954] ? bpf_prog_test_run_raw_tp+0x2d0/0x2d0
    [ 92.694639] ? __fget_light+0xa1/0x100
    [ 92.695162] ? bpf_prog_inc+0x23/0x30
    [ 92.695685] ? __sys_bpf+0xb40/0x2c80
    [ 92.696324] ? bpf_link_get_from_fd+0x90/0x90
    [ 92.697150] ? mark_held_locks+0x24/0x90
    [ 92.698007] ? lockdep_hardirqs_on_prepare+0x124/0x220
    [ 92.699045] ? finish_task_switch+0xe6/0x370
    [ 92.700072] ? lockdep_hardirqs_on+0x79/0x100
    [ 92.701233] ? finish_task_switch+0x11d/0x370
    [ 92.702264] ? __switch_to+0x2c0/0x740
    [ 92.703148] ? mark_held_locks+0x24/0x90
    [ 92.704155] ? __x64_sys_bpf+0x45/0x50
    [ 92.705146] ? do_syscall_64+0x35/0x80
    [ 92.706953] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
    [...]

    Turns out that the program rejection from e411901c0b77 ("bpf: allow for tailcalls
    in BPF subprograms for x64 JIT") is buggy since env->prog->aux->tail_call_reachable
    is never true. Commit ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall
    handling in JIT") added a tracker into check_max_stack_depth() which propagates
    the tail_call_reachable condition throughout the subprograms. This info is then
    assigned to the subprogram's func[i]->aux->tail_call_reachable. However, in the
    case of the rejection check upon JIT failure, env->prog->aux->tail_call_reachable
    is used. func[0]->aux->tail_call_reachable which represents the main program's
    information did not propagate this to the outer env->prog->aux, though. Add this
    propagation into check_max_stack_depth() where it needs to belong so that the
    check can be done reliably.

    Fixes: ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT")
    Fixes: e411901c0b77 ("bpf: allow for tailcalls in BPF subprograms for x64 JIT")
    Co-developed-by: John Fastabend <john.fastabend@gmail.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: John Fastabend <john.fastabend@gmail.com>
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>
    Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
    Link: https://lore.kernel.org/bpf/618c34e3163ad1a36b1e82377576a6081e182f25.1626123173.git.daniel@iogearbox.net
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/bpf/verifier.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
    index d8a6fcd28e39..e6db39a00de2 100644
    --- a/kernel/bpf/verifier.c
    +++ b/kernel/bpf/verifier.c
    @@ -3675,6 +3675,8 @@ continue_func:
    if (tail_call_reachable)
    for (j = 0; j < frame; j++)
    subprog[ret_prog[j]].tail_call_reachable = true;
    + if (subprog[0].tail_call_reachable)
    + env->prog->aux->tail_call_reachable = true;

    /* end of for() loop means the last insn of the 'subprog'
    * was reached. Doesn't matter whether it was JA or EXIT
    --
    2.30.2


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