On 4/24/20 5:31 AM, Andrey Ignatov wrote:

Ma Xinjian max.xinjian@intel.com [Thu, 2020-04-23 02:12 -0700]:

...

Hi,  Andrey.

I noticed you add test_sysctl to tools/bpf, so drop this problem to you.

When I run selftests: bpf: test_sysctl, failed with "(test_sysctl.c:1490: errno: Permission denied) >>> Loading program (./test_sysctl_prog.o) error."

Testing env: "Debian GNU/Linux 9 (stretch)"

kernel: 5.7.0-rc2    5.7.0-rc1  5.6  both failed

Whole run log and kconfig please see the attatchment.

Error info

root@vm-snb-42 /usr/src/perf_selftests-x86_64-rhel-7.6-kselftests-ae83d0b416db002fe95601e7f97f64b59514d936/tools/testing/selftests/bpf#
./test_sysctl

Test case: sysctl wrong attach_type .. [PASS]
Test case: sysctl:read allow all .. [PASS]
Test case: sysctl:read deny all .. [PASS]

[snip]

libbpf: -- END LOG --
libbpf: failed to load program 'cgroup/sysctl'
libbpf: failed to load object './test_sysctl_prog.o'
(test_sysctl.c:1490: errno: Permission denied) >>> Loading program
(./test_sysctl_prog.o) error.

Test case: C prog: read tcp_mem .. [FAIL]
Summary: 37 PASSED, 3 FAILED

Hi Ma,

I can not reproduce it. I built 5.7.0-rc2 with your config (with minor changes to just make it work with my qemu-setup, specifically CONFIG_EXT4_FS=y), built tests and run it, no failures:

root@arch-fb-vm1:/home/rdna/bpf-next/tools/testing/selftests/bpf uname -srm Linux 5.7.0-rc2 x86_64 root@arch-fb-vm1:/home/rdna/bpf-next/tools/testing/selftests/bpf ./test_sysctl ... Test case: C prog: deny all writes .. [PASS] Test case: C prog: deny access by name .. [PASS] Test case: C prog: read tcp_mem .. [PASS] Summary: 40 PASSED, 0 FAILED

Thouhg I see that test_sysctl_prog.o program I have differs from what you have. I attach test_sysctl_prog_xlated.gz with my program.

Specifically the difference starts after the first call to bpf_strtoul.

The code from my prog looks like this (from the first call to bpf_strtoul to the second call to bpf_strtoul):

 71: (85) call bpf_strtoul#110448
 72: (bc) w7 = w0

; if (ret <= 0 || ret > MAX_ULONG_STR_LEN) 73: (bc) w1 = w7 74: (04) w1 += -1 75: (26) if w1 > 0xe goto pc-21 ; off += ret & MAX_ULONG_STR_LEN; 76: (54) w7 &= 15 77: (bf) r1 = r10 78: (07) r1 += -64 ; ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, 79: (0f) r1 += r7 ; tcp_mem + i); 80: (bf) r4 = r10 81: (07) r4 += -80 ; ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, 82: (b7) r2 = 15 83: (b7) r3 = 0 84: (85) call bpf_strtoul#110448

It can be seen that r1 points to stack-64 + r7 that is known to be <15.

This is basically `value + (ret & MAX_ULONG_STR_LEN)` from the C code.

The code from your version of program looks like this:

 70: (85) call bpf_strtoul#106

last_idx 70 first_idx 63 regs=4 stack=0 before 69: (b7) r3 = 0 regs=4 stack=0 before 68: (b7) r2 = 15 71: (bc) w7 = w0 ; if (ret <= 0 || ret > MAX_ULONG_STR_LEN) 72: (bc) w1 = w7 73: (04) w1 += -1 74: (26) if w1 > 0xe goto pc+14 R0=inv(id=0) R1_w=inv(id=0,umax_value=14,var_off=(0x0; 0xf)) R6=inv0 R7_w=inv(id=0,smax_value=2147483647,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R10=fp0 fp-8=mmmmmmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm fp-48=mmmmmmmm fp-56=mmmmmmmm fp-64=mmmmmmmm fp-72=00000000 fp-80=00000000 fp-88=mmmmmmmm ; ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, 75: (bc) w2 = w7 76: (67) r2 <<= 32 77: (77) r2 >>= 32 78: (bf) r1 = r10 ; 79: (07) r1 += -64 ; ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, 80: (0f) r1 += r2 last_idx 80 first_idx 71 regs=4 stack=0 before 79: (07) r1 += -64 regs=4 stack=0 before 78: (bf) r1 = r10 regs=4 stack=0 before 77: (77) r2 >>= 32 regs=4 stack=0 before 76: (67) r2 <<= 32 regs=4 stack=0 before 75: (bc) w2 = w7 regs=80 stack=0 before 74: (26) if w1 > 0xe goto pc+14 regs=80 stack=0 before 73: (04) w1 += -1 regs=80 stack=0 before 72: (bc) w1 = w7 regs=80 stack=0 before 71: (bc) w7 = w0 R0_rw=invP(id=0) R6=inv0 R7=ctx(id=0,off=0,imm=0) R10=fp0 fp-8=mmmmmmmm fp-16=mmmmmmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm fp-48=mmmmmmmm fp-56=mmmmmmmm fp-64=mmmmmmmm fp-72=00000000 fp-80=00000000 fp-88=mmmmmmmm parent didn't have regs=1 stack=0 marks last_idx 70 first_idx 63 regs=1 stack=0 before 70: (85) call bpf_strtoul#106 ; tcp_mem + i); 81: (bf) r4 = r10 82: (07) r4 += -80 ; ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0, 83: (b7) r2 = 15 84: (b7) r3 = 0 85: (85) call bpf_strtoul#106 R1 unbounded indirect variable offset stack access processed 88 insns (limit 1000000) max_states_per_insn 0 total_states 7 peak_states 7 mark_read 6

In this case r1 points to stack-64 + r2 and it seems to me that the state of r2 is the problem, but I don't undesrtand why.

32LSB of r2 seems to be known because: 71: (bc) w7 = w0 72: (bc) w1 = w7 73: (04) w1 += -1 74: (26) if w1 > 0xe goto pc+14 75: (bc) w2 = w7

and 32MSB of r2 are cleared because: 76: (67) r2 <<= 32 77: (77) r2 >>= 32

So it seems to me that r2 has to be known and in (0x0; 0xf) range.

To summarize:

• I see that your program differs what may mean you have different environemnt where you build BPF proga (e.g. different clang/llvm version), FWIW I have clang version 9.0.20190721 (though it's heavily patched facebook version).

Hi, Andrey.

Thank you very much for your quick reply.

I have tried build with 9.0.* clang, but failed with

```

libbpf: failed to find BTF for extern 'CONFIG_BPF_SYSCALL': -2 Error: failed to open BPF object file: 0 Makefile:361: recipe for target '/usr/src/perf_selftests-x86_64-rhel-7.6-kselftests-8f3d9f354286745c751374f5f1fcafee6b3f3136/tools/testing/selftests/bpf/test_skeleton.skel.h' failed ``` This error was tracked in: https://www.spinics.net/lists/netdev/msg646956.html

So I have rebuild with clang 10.0.0. Still the same error.

• I'm not quite sure why verifier rejects your version of the program -- here we would need more eyes. I'm cc'ing Alexei and Daniel.