Re: WARNING: kmalloc bug in bpf_uprobe_multi_link_attach

Jiri Olsa
2023-12-11T13:01:55Z

On Mon, Dec 11, 2023 at 07:29:40PM +0800, Hou Tao wrote:

SNIP

>
> It seems a big attr->link_create.uprobe_multi.cnt is passed to
> bpf_uprobe_multi_link_attach(). Could you please try the first patch in
> the following patch set ?
>
> https://lore.kernel.org/bpf/20231211112843.4147157-1-houtao@huaweicloud.com/T/#t
> > [ 68.389633][ T8223] ? __might_fault+0x13f/0x1a0
> > [ 68.390129][ T8223] ? bpf_kprobe_multi_link_attach+0x10/0x10
>
> SNIP
> > res = syscall(__NR_bpf, /*cmd=*/5ul, /*arg=*/0x20000140ul, /*size=*/0x90ul);
> > if (res != -1) r[0] = res;
> > memcpy((void*)0x20000000, "./file0\000", 8);
> > syscall(__NR_creat, /*file=*/0x20000000ul, /*mode=*/0ul);
> > *(uint32_t*)0x20000340 = r[0];
> > *(uint32_t*)0x20000344 = 0;
> > *(uint32_t*)0x20000348 = 0x30;
> > *(uint32_t*)0x2000034c = 0;
> > *(uint64_t*)0x20000350 = 0x20000080;
> > memcpy((void*)0x20000080, "./file0\000", 8);
>
> 0x20000350 is the address of attr->link_create.uprobe_multi.path.
> > *(uint64_t*)0x20000358 = 0x200000c0;
> > *(uint64_t*)0x200000c0 = 0;
> > *(uint64_t*)0x20000360 = 0;
> > *(uint64_t*)0x20000368 = 0;
> > *(uint32_t*)0x20000370 = 0xffffff1f;
>
> The value of attr->link_create.uprobe_multi.cnt is 0xffffff1f, so
> 0xffffff1f * sizeof(bpf_uprobe) will be greater than INT_MAX, and
> triggers the warning in mm/util.c:
>
>         /* Don't even allow crazy sizes */
>         if (unlikely(size > INT_MAX)) {
>                 WARN_ON_ONCE(!(flags & __GFP_NOWARN));
>                 return NULL;
>         }
>
> Adding __GFP_NOWARN when doing kvcalloc() can fix the warning.

hi,
looks like that's the case.. thanks for fixing that

btw while checking on that I found kprobe_multi bench attach test
takes forever on latest bpf-next/master

test_kprobe_multi_bench_attach:PASS:bpf_program__attach_kprobe_multi_opts 0 nsec
test_kprobe_multi_bench_attach: found 56140 functions
test_kprobe_multi_bench_attach: attached in 89.174s
test_kprobe_multi_bench_attach: detached in 13.245s
#113/1 kprobe_multi_bench_attach/kernel:OK

Masami,
any idea of any change on fprobe/ftrace side recently? I'm going to check ;-)

thanks,
jirka