"Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxx> writes:
> Michael Ellerman wrote:
>> Daniel Borkmann <daniel@xxxxxxxxxxxxx> writes:
>>> On 10/25/21 8:15 AM, Naveen N. Rao wrote:
>>>> Hari Bathini wrote:
>>>>> Running program with bpf-to-bpf function calls results in data access
>>>>> exception (0x300) with the below call trace:
>>>>>
>>>>> [c000000000113f28] bpf_int_jit_compile+0x238/0x750 (unreliable)
>>>>> [c00000000037d2f8] bpf_check+0x2008/0x2710
>>>>> [c000000000360050] bpf_prog_load+0xb00/0x13a0
>>>>> [c000000000361d94] __sys_bpf+0x6f4/0x27c0
>>>>> [c000000000363f0c] sys_bpf+0x2c/0x40
>>>>> [c000000000032434] system_call_exception+0x164/0x330
>>>>> [c00000000000c1e8] system_call_vectored_common+0xe8/0x278
>>>>>
>>>>> as bpf_int_jit_compile() tries writing to write protected JIT code
>>>>> location during the extra pass.
>>>>>
>>>>> Fix it by holding off write protection of JIT code until the extra
>>>>> pass, where branch target addresses fixup happens.
>>>>>
>>>>> Cc: stable@xxxxxxxxxxxxxxx
>>>>> Fixes: 62e3d4210ac9 ("powerpc/bpf: Write protect JIT code")
>>>>> Signed-off-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
>>>>> ---
>>>>> arch/powerpc/net/bpf_jit_comp.c | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> Thanks for the fix!
>>>>
>>>> Reviewed-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
>>>
>>> LGTM, I presume this fix will be routed via Michael.
>>
>> Thanks for reviewing, I've picked it up.
>>
>>> BPF selftests have plenty of BPF-to-BPF calls in there, too bad this was
>>> caught so late. :/
>>
>> Yeah :/
>>
>> STRICT_KERNEL_RWX is not on by default in all our defconfigs, so that's
>> probably why no one caught it.
>
> Yeah, sorry - we should have caught this sooner.
>
>>
>> I used to run the BPF selftests but they stopped building for me a while
>> back, I'll see if I can get them going again.
>
> Ravi had started looking into getting the selftests working well before
> he left. I will take a look at this.
Thanks.
I got them building with something like:
- turning on DEBUG_INFO and DEBUG_INFO_BTF and rebuilding vmlinux
- grabbing clang 13 from:
https://github.com/llvm/llvm-project/releases/download/llvmorg-13.0.0/clang+llvm-13.0.0-powerpc64le-linux-ubuntu-18.04.tar.xz
- PATH=$HOME/clang+llvm-13.0.0-powerpc64le-linux-ubuntu-18.04/bin/:$PATH
- apt install:
- libelf-dev
- dwarves
- python-docutils
- libcap-dev
The DEBUG_INFO requirement is a bit of a pain for me. I generally don't
build with that enabled, because the resulting kernels are stupidly
large. I'm not sure if that's a hard requirement, or if the vmlinux has
to match the running kernel exactly?
There is logic in tools/testing/bpf/Makefile to use VMLINUX_H instead of
extracting the BTF from the vmlinux (line 247), but AFAICS that's
unreachable since 1a3449c19407 ("selftests/bpf: Clarify build error if
no vmlinux"), which makes it a hard error to not have a VMLINUX_BTF.
cheers
