Re: bpf: shift-out-of-bounds in tnum_rshift()
From: Hao Sun
Date: Wed Oct 25 2023 - 09:20:48 EST
On Wed, Oct 25, 2023 at 2:31 PM Hao Sun <sunhao.th@xxxxxxxxx> wrote:
>
> On Tue, Oct 24, 2023 at 2:40 PM Hao Sun <sunhao.th@xxxxxxxxx> wrote:
> >
> > Hi,
> >
> > The following program can trigger a shift-out-of-bounds in
> > tnum_rshift(), called by scalar32_min_max_rsh():
> >
> > 0: (bc) w0 = w1
> > 1: (bf) r2 = r0
> > 2: (18) r3 = 0xd
> > 4: (bc) w4 = w0
> > 5: (bf) r5 = r0
> > 6: (bf) r7 = r3
> > 7: (bf) r8 = r4
> > 8: (2f) r8 *= r5
> > 9: (cf) r5 s>>= r5
> > 10: (a6) if w8 < 0xfffffffb goto pc+10
> > 11: (1f) r7 -= r5
> > 12: (71) r6 = *(u8 *)(r1 +17)
> > 13: (5f) r3 &= r8
> > 14: (74) w2 >>= 30
> > 15: (1f) r7 -= r5
> > 16: (5d) if r8 != r6 goto pc+4
> > 17: (c7) r8 s>>= 5
> > 18: (cf) r0 s>>= r0
> > 19: (7f) r0 >>= r0
> > 20: (7c) w5 >>= w8 # shift-out-bounds here
> > 21: exit
> >
>
> Here are the c macros for the above program in case anyone needs this:
>
> // 0: (bc) w0 = w1
> BPF_MOV32_REG(BPF_REG_0, BPF_REG_1),
> // 1: (bf) r2 = r0
> BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
> // 2: (18) r3 = 0xd
> BPF_LD_IMM64(BPF_REG_3, 0xd),
> // 4: (bc) w4 = w0
> BPF_MOV32_REG(BPF_REG_4, BPF_REG_0),
> // 5: (bf) r5 = r0
> BPF_MOV64_REG(BPF_REG_5, BPF_REG_0),
> // 6: (bf) r7 = r3
> BPF_MOV64_REG(BPF_REG_7, BPF_REG_3),
> // 7: (bf) r8 = r4
> BPF_MOV64_REG(BPF_REG_8, BPF_REG_4),
> // 8: (2f) r8 *= r5
> BPF_ALU64_REG(BPF_MUL, BPF_REG_8, BPF_REG_5),
> // 9: (cf) r5 s>>= r5
> BPF_ALU64_REG(BPF_ARSH, BPF_REG_5, BPF_REG_5),
> // 10: (a6) if w8 < 0xfffffffb goto pc+10
> BPF_JMP32_IMM(BPF_JLT, BPF_REG_8, 0xfffffffb, 10),
> // 11: (1f) r7 -= r5
> BPF_ALU64_REG(BPF_SUB, BPF_REG_7, BPF_REG_5),
> // 12: (71) r6 = *(u8 *)(r1 +17)
> BPF_LDX_MEM(BPF_B, BPF_REG_6, BPF_REG_1, 17),
> // 13: (5f) r3 &= r8
> BPF_ALU64_REG(BPF_AND, BPF_REG_3, BPF_REG_8),
> // 14: (74) w2 >>= 30
> BPF_ALU32_IMM(BPF_RSH, BPF_REG_2, 30),
> // 15: (1f) r7 -= r5
> BPF_ALU64_REG(BPF_SUB, BPF_REG_7, BPF_REG_5),
> // 16: (5d) if r8 != r6 goto pc+4
> BPF_JMP_REG(BPF_JNE, BPF_REG_8, BPF_REG_6, 4),
> // 17: (c7) r8 s>>= 5
> BPF_ALU64_IMM(BPF_ARSH, BPF_REG_8, 5),
> // 18: (cf) r0 s>>= r0
> BPF_ALU64_REG(BPF_ARSH, BPF_REG_0, BPF_REG_0),
> // 19: (7f) r0 >>= r0
> BPF_ALU64_REG(BPF_RSH, BPF_REG_0, BPF_REG_0),
> // 20: (7c) w5 >>= w8
> BPF_ALU32_REG(BPF_RSH, BPF_REG_5, BPF_REG_8),
> BPF_EXIT_INSN()
>
> > After load:
> > ================================================================================
> > UBSAN: shift-out-of-bounds in kernel/bpf/tnum.c:44:9
> > shift exponent 255 is too large for 64-bit type 'long long unsigned int'
> > CPU: 2 PID: 8574 Comm: bpf-test Not tainted
> > 6.6.0-rc5-01400-g7c2f6c9fb91f-dirty #21
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> > Call Trace:
> > <TASK>
> > __dump_stack lib/dump_stack.c:88 [inline]
> > dump_stack_lvl+0x8e/0xb0 lib/dump_stack.c:106
> > ubsan_epilogue lib/ubsan.c:217 [inline]
> > __ubsan_handle_shift_out_of_bounds+0x15a/0x2f0 lib/ubsan.c:387
> > tnum_rshift.cold+0x17/0x32 kernel/bpf/tnum.c:44
> > scalar32_min_max_rsh kernel/bpf/verifier.c:12999 [inline]
> > adjust_scalar_min_max_vals kernel/bpf/verifier.c:13224 [inline]
> > adjust_reg_min_max_vals+0x1936/0x5d50 kernel/bpf/verifier.c:13338
> > do_check kernel/bpf/verifier.c:16890 [inline]
> > do_check_common+0x2f64/0xbb80 kernel/bpf/verifier.c:19563
> > do_check_main kernel/bpf/verifier.c:19626 [inline]
> > bpf_check+0x65cf/0xa9e0 kernel/bpf/verifier.c:20263
> > bpf_prog_load+0x110e/0x1b20 kernel/bpf/syscall.c:2717
> > __sys_bpf+0xfcf/0x4380 kernel/bpf/syscall.c:5365
> > __do_sys_bpf kernel/bpf/syscall.c:5469 [inline]
> > __se_sys_bpf kernel/bpf/syscall.c:5467 [inline]
> > __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:5467
> > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > RIP: 0033:0x5610511e23cd
> > Code: 24 80 00 00 00 48 0f 42 d0 48 89 94 24 68 0c 00 00 b8 41 01 00
> > 00 bf 05 00 00 00 ba 90 00 00 00 48 8d b44
> > RSP: 002b:00007f5357fc7820 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> > RAX: ffffffffffffffda RBX: 0000000000000095 RCX: 00005610511e23cd
> > RDX: 0000000000000090 RSI: 00007f5357fc8410 RDI: 0000000000000005
> > RBP: 0000000000000000 R08: 00007f5357fca458 R09: 00007f5350005520
> > R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000002b
> > R13: 0000000d00000000 R14: 000000000000002b R15: 000000000000002b
> > </TASK>
> >
Here is another similar one, which can probably be fixed in the same
patch. Build the kernel with UBSAN and run the following repro can
easily reproduce this.
C reproducer: https://pastebin.com/raw/zNfHaBnj
================================================================================
UBSAN: shift-out-of-bounds in kernel/bpf/verifier.c:13049:63
shift exponent 55 is too large for 32-bit type 'int'
CPU: 3 PID: 8614 Comm: poc Not tainted 6.6.0-rc5-01400-g7c2f6c9fb91f-dirty #22
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x8e/0xb0 lib/dump_stack.c:106
ubsan_epilogue lib/ubsan.c:217 [inline]
__ubsan_handle_shift_out_of_bounds+0x15a/0x2f0 lib/ubsan.c:387
scalar32_min_max_arsh kernel/bpf/verifier.c:13049 [inline]
adjust_scalar_min_max_vals kernel/bpf/verifier.c:13237 [inline]
adjust_reg_min_max_vals.cold+0x116/0x353 kernel/bpf/verifier.c:13338
do_check kernel/bpf/verifier.c:16890 [inline]
do_check_common+0x2f64/0xbb80 kernel/bpf/verifier.c:19563
do_check_main kernel/bpf/verifier.c:19626 [inline]
bpf_check+0x65cf/0xa9e0 kernel/bpf/verifier.c:20263
bpf_prog_load+0x110e/0x1b20 kernel/bpf/syscall.c:2717
__sys_bpf+0xfcf/0x4380 kernel/bpf/syscall.c:5365
__do_sys_bpf kernel/bpf/syscall.c:5469 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5467 [inline]
__x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:5467
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x43b0a9
Code: 48 83 c4 28 c3 e8 17 1a 00 00 0f 1f 80 00 00 00 00 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 48
RSP: 002b:00007fffec705b18 EFLAGS: 00000202 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007fffec705ff8 RCX: 000000000043b0a9
RDX: 0000000000000080 RSI: 00007fffec705b30 RDI: 0000000000000005
RBP: 00007fffec705c00 R08: 0000000400000002 R09: 0000003e00000000
R10: 00000000000000fc R11: 0000000000000202 R12: 0000000000000001
R13: 00007fffec705fe8 R14: 0000000000000001 R15: 0000000000000001
</TASK>