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

[Puranjay Mohan <puranjay@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 1021 bytes --]


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.

Thanks,
Puranjay

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 255 bytes --]