netdev - Re: [PATCH bpf] bpf: arm64: clear prog->jited

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Message-ID: <CAPhsuW4vhjb6TAtT4XqWVqdbBrAVMuaZrvVfZZK=jyaoBaxKMQ@mail.gmail.com>
Date:   Tue, 31 May 2022 15:17:46 -0700
From:   Song Liu <song@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>, bpf <bpf@...r.kernel.org>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH bpf] bpf: arm64: clear prog->jited_len along prog->jited

On Tue, May 31, 2022 at 2:51 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> syzbot reported an illegal copy_to_user() attempt
> from bpf_prog_get_info_by_fd() [1]
>
> There was no repro yet on this bug, but I think
> that commit 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns")
> is exposing a prior bug in bpf arm64.
>
> bpf_prog_get_info_by_fd() looks at prog->jited_len
> to determine if the JIT image can be copied out to user space.
>
> My theory is that syzbot managed to get a prog where prog->jited_len
> has been set to 43, while prog->bpf_func has ben cleared.
>
> It is not clear why copy_to_user(uinsns, NULL, ulen) is triggering
> this particular warning.
> I thought find_vma_area(NULL) would not find a vm_struct.
> As we do not hold vmap_area_lock spinlock, it might be possible
> that the found vm_struct was garbage.
>
> [1]
> usercopy: Kernel memory exposure attempt detected from vmalloc (offset 792633534417210172, size 43)!
> kernel BUG at mm/usercopy.c:101!
> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 0 PID: 25002 Comm: syz-executor.1 Not tainted 5.18.0-syzkaller-10139-g8291eaafed36 #0
> Hardware name: linux,dummy-virt (DT)
> pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : usercopy_abort+0x90/0x94 mm/usercopy.c:101
> lr : usercopy_abort+0x90/0x94 mm/usercopy.c:89
> sp : ffff80000b773a20
> x29: ffff80000b773a30 x28: faff80000b745000 x27: ffff80000b773b48
> x26: 0000000000000000 x25: 000000000000002b x24: 0000000000000000
> x23: 00000000000000e0 x22: ffff80000b75db67 x21: 0000000000000001
> x20: 000000000000002b x19: ffff80000b75db3c x18: 00000000fffffffd
> x17: 2820636f6c6c616d x16: 76206d6f72662064 x15: 6574636574656420
> x14: 74706d6574746120 x13: 2129333420657a69 x12: 73202c3237313031
> x11: 3237313434333533 x10: 3336323937207465 x9 : 657275736f707865
> x8 : ffff80000a30c550 x7 : ffff80000b773830 x6 : ffff80000b773830
> x5 : 0000000000000000 x4 : ffff00007fbbaa10 x3 : 0000000000000000
> x2 : 0000000000000000 x1 : f7ff000028fc0000 x0 : 0000000000000064
> Call trace:
>  usercopy_abort+0x90/0x94 mm/usercopy.c:89
>  check_heap_object mm/usercopy.c:186 [inline]
>  __check_object_size mm/usercopy.c:252 [inline]
>  __check_object_size+0x198/0x36c mm/usercopy.c:214
>  check_object_size include/linux/thread_info.h:199 [inline]
>  check_copy_size include/linux/thread_info.h:235 [inline]
>  copy_to_user include/linux/uaccess.h:159 [inline]
>  bpf_prog_get_info_by_fd.isra.0+0xf14/0xfdc kernel/bpf/syscall.c:3993
>  bpf_obj_get_info_by_fd+0x12c/0x510 kernel/bpf/syscall.c:4253
>  __sys_bpf+0x900/0x2150 kernel/bpf/syscall.c:4956
>  __do_sys_bpf kernel/bpf/syscall.c:5021 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5019 [inline]
>  __arm64_sys_bpf+0x28/0x40 kernel/bpf/syscall.c:5019
>  __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
>  invoke_syscall+0x48/0x114 arch/arm64/kernel/syscall.c:52
>  el0_svc_common.constprop.0+0x44/0xec arch/arm64/kernel/syscall.c:142
>  do_el0_svc+0xa0/0xc0 arch/arm64/kernel/syscall.c:206
>  el0_svc+0x44/0xb0 arch/arm64/kernel/entry-common.c:624
>  el0t_64_sync_handler+0x1ac/0x1b0 arch/arm64/kernel/entry-common.c:642
>  el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:581
> Code: aa0003e3 d00038c0 91248000 97fff65f (d4210000)
>
> Fixes: db496944fdaa ("bpf: arm64: add JIT support for multi-function programs")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  arch/arm64/net/bpf_jit_comp.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index 8ab4035dea2742b704dc7501b0b2128320899b1e..42f2e9a8616c3095609c182e6f50defdbe862b46 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -1478,6 +1478,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
>                         bpf_jit_binary_free(header);
>                         prog->bpf_func = NULL;
>                         prog->jited = 0;
> +                       prog->jited_len = 0;
>                         goto out_off;
>                 }
>                 bpf_jit_binary_lock_ro(header);
> --
> 2.36.1.255.ge46751e96f-goog
>