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!
