Re: [PATCH bpf] selftests/bpf: DENYLIST.aarch64: Remove fexit_sleep

[Daniel Borkmann]

On 7/11/24 4:00 PM, Puranjay Mohan wrote:
> Hi,
> I was able find the root cause of this bug and will send a fix soon!
>
> > Unable to handle kernel paging request at virtual address ffff0000c2a80e68
>
> We are running this test on Qemu with '-cpu max', this means 52-bit
> virtual addresses are being used.
>
> The trampolines generation code has the following two lines:
>
> 		emit_addr_mov_i64(A64_R(0), (const u64)im, ctx);
> 		emit_call((const u64)__bpf_tramp_enter, ctx);
>
> here the address of struct bpf_tramp_image is moved to R0 and passed as
> an argument to __bpf_tramp_enter().
>
> emit_addr_mov_i64() assumes that the address passed to it is in the
> vmalloc space and uses at most 48 bits. It sets all the remaining bits
> to 1.
>
> but struct bpf_tramp_image is allocated using kzalloc() and when 52-bit
> VAs are used, its address is not guaranteed to be 48-bit, therefore we
> see this bug, where  0xfff[0]0000c2a80e68 is converted to
> 0xfff[f]0000c2a80e68 when the trampoline is generated.
>
> The fix would be use emit_a64_mov_i64() for moving this address into R0.

Excellent find!