Re: [PATCH bpf-next v3 0/3] bpf: Report arena faults to BPF streams

[Puranjay Mohan <puranjay@kernel.org>]

Puranjay Mohan <puranjay@kernel.org> writes:

> Changes in v2->v3:
> v2: https://lore.kernel.org/all/20250811111828.13836-1-puranjay@kernel.org/
> - Improved the selftest to check the exact fault address
> - Dropped BPF_NO_KFUNC_PROTOTYPES and bpf_arena_alloc/free_pages() usage
> - Rebased on bpf-next/master
>
> Changes in v1->v2:
> v1: https://lore.kernel.org/all/20250806085847.18633-1-puranjay@kernel.org/
> - Changed variable and mask names for consistency (Yonghong)
> - Added Acked-by: Yonghong Song <yonghong.song@linux.dev> on two patches
>
> This set adds the support of reporting page faults inside arena to BPF
> stderr stream. The reported address is the one that a user would expect
> to see if they pass it to bpf_printk();
>
> Here is an example output from a stream and bpf_printk()
>
> ERROR: Arena WRITE access at unmapped address 0xdeaddead0000
> CPU: 9 UID: 0 PID: 502 Comm: test_progs
> Call trace:
> bpf_stream_stage_dump_stack+0xc0/0x150
> bpf_prog_report_arena_violation+0x98/0xf0
> ex_handler_bpf+0x5c/0x78
> fixup_exception+0xf8/0x160
> __do_kernel_fault+0x40/0x188
> do_bad_area+0x70/0x88
> do_translation_fault+0x54/0x98
> do_mem_abort+0x4c/0xa8
> el1_abort+0x44/0x70
> el1h_64_sync_handler+0x50/0x108
> el1h_64_sync+0x6c/0x70
> bpf_prog_a64a9778d31b8e88_stream_arena_write_fault+0x84/0xc8
>   *(page) = 1; @ stream.c:100
> bpf_prog_test_run_syscall+0x100/0x328
> __sys_bpf+0x508/0xb98
> __arm64_sys_bpf+0x2c/0x48
> invoke_syscall+0x50/0x120
> el0_svc_common.constprop.0+0x48/0xf8
> do_el0_svc+0x28/0x40
> el0_svc+0x48/0xf8
> el0t_64_sync_handler+0xa0/0xe8
> el0t_64_sync+0x198/0x1a0
>
> Same address is seen by using bpf_printk():
>
> 1389.078831: bpf_trace_printk: Read Address: 0xdeaddead0000
>
> To make this possible, some extra metadata has to be passed to the bpf
> exception handler, so the bpf exception handling mechanism for both
> x86-64 and arm64 have been improved in this set.
>
> The streams selftest has been updated to also test this new feature.
>
> Puranjay Mohan (3):
>   bpf: arm64: simplify exception table handling
>   bpf: Report arena faults to BPF stderr
>   selftests/bpf: Add tests for arena fault reporting
>

Please ignore this version!!!

I forgot to fix a build issue in this version, it triggers when
BPF_SYSCALL is disabled but JIT is enabled. I have sent another version
to fix this.

v4 including the fix: https://lore.kernel.org/all/20250827153728.28115-1-puranjay@kernel.org/

Thanks,
Puranjay