[PATCH bpf-next 0/1] arm64: Add BPF exception tables

[Alexei Starovoitov]

On Wed, Jun 16, 2021 at 11:58 PM Ravi Bangoria
<ravi.bangoria at linux.ibm.com> wrote:
>
>    $ dmesg
>    [  166.864325] BUG: unable to handle page fault for address: 0000000000d12345
>    [  166.864336] #PF: supervisor read access in kernel mode
>    [  166.864338] #PF: error_code(0x0000) - not-present page
>
> 0xd12345 is unallocated userspace address. Similarly, I also tried with

that's unfortunately expected, since this is a user address.

> p->dte = (void *)0xffffffffc1234567 after confirming it's not allocated
> to kernel or any module address. I see the same failure with it too.

This one is surprising though. Sounds like a bug in exception table
construction. Can you debug it to see what's causing it?
First check that do_kern_addr_fault() is invoked in this case.
And then fixup_exception() and why search_bpf_extables()
cannot find it.
Separately we probably need to replace the NULL check
with addr >= TASK_SIZE_MAX to close this issue though it's a bit artificial.