[PATCH bpf-next v7 0/6] bpf: report arena faults to BPF streams

[Puranjay Mohan <puranjay@kernel.org>]

Changes in v6->v7:
v6: https://lore.kernel.org/all/20250908163638.23150-1-puranjay@kernel.org/
- Added comments about the usage of arena_reg in x86 and arm64 jits. (Alexei)
- Used clear_lo32() for clearing the lower 32-bits of user_vm_start. (Alexei)
- Moved update of the old tests to use __stderr to a separate commit (Eduard)
- Used test__skip() in prog_tests/stream.c (Eduard)
- Start a sub-test for read / write

Changes in v5->v6:
v5: https://lore.kernel.org/all/20250901193730.43543-1-puranjay@kernel.org/
- Introduces __stderr and __stdout for easy testing of bpf streams
  (Eduard)
- Add more test cases for arena fault reporting (subprog and callback)
- Fix main_prog_aux usage and return main_prog from find_from_stack_cb
  (Kumar)
- Properly fix the build issue reported by kernel test robot

Changes in v4->v5:
v4: https://lore.kernel.org/all/20250827153728.28115-1-puranjay@kernel.org/
- Added patch 2 to introducing main_prog_aux for easier access to
  streams.
- Fixed bug in fault handlers when arena_reg == dst_reg
- Updated selftest to check test above edge case.
- Added comments about the usage of barrier_var() in code and commit
  message.

Changes in v3->v4:
v3: https://lore.kernel.org/all/20250827150113.15763-1-puranjay@kernel.org/
- Fixed a build issue when CONFIG_BPF_JIT=y and # CONFIG_BPF_SYSCALL is
  not set

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 the stderr 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 printed by 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 test this new feature.

Puranjay Mohan (6):
  bpf: arm64: simplify exception table handling
  bpf: core: introduce main_prog_aux for stream access
  bpf: Report arena faults to BPF stderr
  selftests: bpf: introduce __stderr and __stdout
  selftests: bpf: use __stderr in stream error tests
  selftests/bpf: Add tests for arena fault reporting

 arch/arm64/net/bpf_jit_comp.c                 |  85 +++++++---
 arch/x86/net/bpf_jit_comp.c                   |  85 +++++++++-
 include/linux/bpf.h                           |   7 +
 kernel/bpf/arena.c                            |  30 ++++
 kernel/bpf/core.c                             |   6 +-
 kernel/bpf/verifier.c                         |   1 +
 .../testing/selftests/bpf/prog_tests/stream.c | 131 ++++++---------
 tools/testing/selftests/bpf/progs/bpf_misc.h  |  10 ++
 tools/testing/selftests/bpf/progs/stream.c    | 158 ++++++++++++++++++
 tools/testing/selftests/bpf/test_loader.c     |  90 ++++++++++
 10 files changed, 491 insertions(+), 112 deletions(-)

-- 
2.47.3