Re: BUG: unable to handle kernel paging request in bpf_probe_read_compat_str

Yonghong Song <yonghong.song@xxxxxxxxx> · Wed, 20 Dec 2023 09:50:09 -0800

On 12/20/23 1:19 AM, Hou Tao wrote:
Hi,

On 12/14/2023 11:40 AM, xingwei lee wrote:
Hello I found a bug in net/bpf in the lastest upstream linux and
comfired in the lastest net tree and lastest net bpf titled BUG:
unable to handle kernel paging request in bpf_probe_read_compat_str

If you fix this issue, please add the following tag to the commit:
Reported-by: xingwei Lee <xrivendell7@xxxxxxxxx>

kernel: net 9702817384aa4a3700643d0b26e71deac0172cfd / bpf
2f2fee2bf74a7e31d06fc6cb7ba2bd4dd7753c99
Kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=b50bd31249191be8

in the lastest bpf tree, the crash like:

TITLE: BUG: unable to handle kernel paging request in bpf_probe_read_compat_str
CORRUPTED: false ()
MAINTAINERS (TO): [akpm@xxxxxxxxxxxxxxxxxxxx linux-mm@xxxxxxxxx]
MAINTAINERS (CC): [linux-kernel@xxxxxxxxxxxxxxx]

BUG: unable to handle page fault for address: ff0
Thanks for the report and reproducer. The output is incomplete. It
should be: "BUG: unable to handle page fault for address:
ffffffffff600000". The address is a vsyscall address, so
handle_page_fault() considers that the fault address is in userspace
instead of kernel space, and there will be no fix-up for the exception
and oops happened. Will post a fix and a selftest for it.

There is a proposed fix here:

https://lore.kernel.org/bpf/87r0jwquhv.ffs@tglx/

Not sure the fix in the above link is merged to some upstream branch or not.

#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD cf7a067 P4D cf7a067 PUD cf7c067 PMD cf9f067 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8219 Comm: 9de Not tainted 6.7.0-rc41
Hardware name: QEMU Standard PC (i440FX + PIIX, 4
RIP: 0010:strncpy_from_kernel_nofault+0xc4/0x270 mm/maccess.c:91
Code: 83 85 6c 17 00 00 01 48 8b 2c 24 eb 18 e8 0
RSP: 0018:ffffc900114e7ac0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffc900114e7b30 RCX:2
RDX: ffff8880183abcc0 RSI: ffffffff81b8c9c4 RDI:c
RBP: ffffffffff600000 R08: 0000000000000001 R09:0
R10: 0000000000000001 R11: 0000000000000001 R12:8
R13: ffffffffff600000 R14: 0000000000000008 R15:0
FS:  0000000000000000(0000) GS:ffff88823bc00000(0
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600000 CR3: 000000000cf77000 CR4:0
PKRU: 55555554
Call Trace:
<TASK>
bpf_probe_read_kernel_str_common kernel/trace/bpf_trace.c:262 [inline]
____bpf_probe_read_compat_str kernel/trace/bpf_trace.c:310 [inline]
bpf_probe_read_compat_str+0x12f/0x170 kernel/trace/bpf_trace.c:303
bpf_prog_f17ebaf3f5f7baf8+0x42/0x44
bpf_dispatcher_nop_func include/linux/bpf.h:1196 [inline]
__bpf_prog_run include/linux/filter.h:651 [inline]
bpf_prog_run include/linux/filter.h:658 [inline]
__bpf_trace_run kernel/trace/bpf_trace.c:2307 [inline]
bpf_trace_run2+0x14e/0x410 kernel/trace/bpf_trace.c:2346
trace_kfree include/trace/events/kmem.h:94 [inline]
kfree+0xec/0x150 mm/slab_common.c:1043
vma_numab_state_free include/linux/mm.h:638 [inline]
__vm_area_free+0x3e/0x140 kernel/fork.c:525
remove_vma+0x128/0x170 mm/mmap.c:146
exit_mmap+0x453/0xa70 mm/mmap.c:3332
__mmput+0x12a/0x4d0 kernel/fork.c:1349
mmput+0x62/0x70 kernel/fork.c:1371
exit_mm kernel/exit.c:567 [inline]
do_exit+0x9aa/0x2ac0 kernel/exit.c:858
do_group_exit+0xd4/0x2a0 kernel/exit.c:1021
__do_sys_exit_group kernel/exit.c:1032 [inline]
__se_sys_exit_group kernel/exit.c:1030 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1030
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x41/0x110 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

=* repro.c =*
// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE

#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

#ifndef __NR_bpf
#define __NR_bpf 321
#endif

#define BITMASK(bf_off, bf_len) (((1ull << (bf_len)) - 1) << (bf_off))
#define STORE_BY_BITMASK(type, htobe, addr, val, bf_off, bf_len)     \
  *(type*)(addr) =                                                   \
      htobe((htobe(*(type*)(addr)) & ~BITMASK((bf_off), (bf_len))) | \
            (((type)(val) << (bf_off)) & BITMASK((bf_off), (bf_len))))

uint64_t r[1] = {0xffffffffffffffff};

int main(void) {
  syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
          /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
  syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul, /*prot=*/7ul,
          /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
  syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
          /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
  intptr_t res = 0;
  *(uint32_t*)0x200000c0 = 0x11;
  *(uint32_t*)0x200000c4 = 0xb;
  *(uint64_t*)0x200000c8 = 0x20000180;
  *(uint8_t*)0x20000180 = 0x18;
  STORE_BY_BITMASK(uint8_t, , 0x20000181, 0, 0, 4);
  STORE_BY_BITMASK(uint8_t, , 0x20000181, 0, 4, 4);
  *(uint16_t*)0x20000182 = 0;
  *(uint32_t*)0x20000184 = 0;
  *(uint8_t*)0x20000188 = 0;
  *(uint8_t*)0x20000189 = 0;
  *(uint16_t*)0x2000018a = 0;
  *(uint32_t*)0x2000018c = 0;
  *(uint8_t*)0x20000190 = 0x18;
  STORE_BY_BITMASK(uint8_t, , 0x20000191, 1, 0, 4);
  STORE_BY_BITMASK(uint8_t, , 0x20000191, 0, 4, 4);
  *(uint16_t*)0x20000192 = 0;
  *(uint32_t*)0x20000194 = 0x25702020;
  *(uint8_t*)0x20000198 = 0;
  *(uint8_t*)0x20000199 = 0;
  *(uint16_t*)0x2000019a = 0;
  *(uint32_t*)0x2000019c = 0x20202000;
  STORE_BY_BITMASK(uint8_t, , 0x200001a0, 3, 0, 3);
  STORE_BY_BITMASK(uint8_t, , 0x200001a0, 3, 3, 2);
  STORE_BY_BITMASK(uint8_t, , 0x200001a0, 3, 5, 3);
  STORE_BY_BITMASK(uint8_t, , 0x200001a1, 0xa, 0, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001a1, 1, 4, 4);
  *(uint16_t*)0x200001a2 = 0xfff8;
  *(uint32_t*)0x200001a4 = 0;
  STORE_BY_BITMASK(uint8_t, , 0x200001a8, 7, 0, 3);
  STORE_BY_BITMASK(uint8_t, , 0x200001a8, 1, 3, 1);
  STORE_BY_BITMASK(uint8_t, , 0x200001a8, 0xb, 4, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001a9, 1, 0, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001a9, 0xa, 4, 4);
  *(uint16_t*)0x200001aa = 0;
  *(uint32_t*)0x200001ac = 0;
  STORE_BY_BITMASK(uint8_t, , 0x200001b0, 7, 0, 3);
  STORE_BY_BITMASK(uint8_t, , 0x200001b0, 0, 3, 1);
  STORE_BY_BITMASK(uint8_t, , 0x200001b0, 0, 4, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001b1, 1, 0, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001b1, 0, 4, 4);
  *(uint16_t*)0x200001b2 = 0;
  *(uint32_t*)0x200001b4 = 0xfffffff8;
  STORE_BY_BITMASK(uint8_t, , 0x200001b8, 7, 0, 3);
  STORE_BY_BITMASK(uint8_t, , 0x200001b8, 0, 3, 1);
  STORE_BY_BITMASK(uint8_t, , 0x200001b8, 0xb, 4, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001b9, 2, 0, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001b9, 0, 4, 4);
  *(uint16_t*)0x200001ba = 0;
  *(uint32_t*)0x200001bc = 8;
  STORE_BY_BITMASK(uint8_t, , 0x200001c0, 7, 0, 3);
  STORE_BY_BITMASK(uint8_t, , 0x200001c0, 0, 3, 1);
  STORE_BY_BITMASK(uint8_t, , 0x200001c0, 0xb, 4, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001c1, 3, 0, 4);
  STORE_BY_BITMASK(uint8_t, , 0x200001c1, 0, 4, 4);
  *(uint16_t*)0x200001c2 = 0;
  *(uint32_t*)0x200001c4 = 0xff600000;
  *(uint8_t*)0x200001c8 = 0x85;
  *(uint8_t*)0x200001c9 = 0;
  *(uint16_t*)0x200001ca = 0;
  *(uint32_t*)0x200001cc = 0x2d;
  *(uint8_t*)0x200001d0 = 0x95;
  *(uint8_t*)0x200001d1 = 0;
  *(uint16_t*)0x200001d2 = 0;
  *(uint32_t*)0x200001d4 = 0;
  *(uint64_t*)0x200000d0 = 0x20000200;
  memcpy((void*)0x20000200, "GPL\000", 4);
  *(uint32_t*)0x200000d8 = 0;
  *(uint32_t*)0x200000dc = 0;
  *(uint64_t*)0x200000e0 = 0;
  *(uint32_t*)0x200000e8 = 0;
  *(uint32_t*)0x200000ec = 0;
  memset((void*)0x200000f0, 0, 16);
  *(uint32_t*)0x20000100 = 0;
  *(uint32_t*)0x20000104 = 0;
  *(uint32_t*)0x20000108 = 0;
  *(uint32_t*)0x2000010c = 0;
  *(uint64_t*)0x20000110 = 0;
  *(uint32_t*)0x20000118 = 0;
  *(uint32_t*)0x2000011c = 0;
  *(uint64_t*)0x20000120 = 0;
  *(uint32_t*)0x20000128 = 0;
  *(uint32_t*)0x2000012c = 0;
  *(uint32_t*)0x20000130 = 0;
  *(uint32_t*)0x20000134 = 0;
  *(uint64_t*)0x20000138 = 0;
  *(uint64_t*)0x20000140 = 0;
  *(uint32_t*)0x20000148 = 0;
  *(uint32_t*)0x2000014c = 0;
  res = syscall(__NR_bpf, /*cmd=*/5ul, /*arg=*/0x200000c0ul, /*size=*/0x90ul);
  if (res != -1) r[0] = res;
  *(uint64_t*)0x20000540 = 0x20000000;
  memcpy((void*)0x20000000, "kfree\000", 6);
  *(uint32_t*)0x20000548 = r[0];
  syscall(__NR_bpf, /*cmd=*/0x11ul, /*arg=*/0x20000540ul, /*size=*/0x10ul);
  return 0;
}

=* repro.txt =*
r0 = bpf$PROG_LOAD(0x5, &(0x7f00000000c0)={0x11, 0xb,
&(0x7f0000000180)=@framed={{}, [@printk={@p, {}, {}, {}, {}, {0x7,
0x0, 0xb, 0x3, 0x0, 0x0, 0xff600000}, {0x85, 0x0, 0x0, 0x2d}}]},
&(0x7f0000000200)='GPL\x00', 0x0, 0x0, 0x0, 0x0, 0x0, '\x00', 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
0x90)
bpf$BPF_RAW_TRACEPOINT_OPEN(0x11,
&(0x7f0000000540)={&(0x7f0000000000)='kfree\x00', r0}, 0x10)

See aslo https://gist.github.com/xrivendell7/7bb1f0a30ccc2899fe7ea34bef882067
I hope it helps.

Best regards.
xingwei Lee

.