bpf: report arena faults to BPF streams #5917
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BPF loads with BPF_PROBE_MEM(SX) can load from unsafe pointers and the JIT adds an exception table entry for the JITed instruction which allows the exeption handler to set the destination register of the load to zero and continue execution from the next instruction. As all arm64 instructions are AARCH64_INSN_SIZE size, the exception handler can just increment the pc by AARCH64_INSN_SIZE without needing the exact address of the instruction following the the faulting instruction. Simplify the exception table usage in arm64 JIT by only saving the destination register in ex->fixup and drop everything related to the fixup_offset. The fault handler is modified to add AARCH64_INSN_SIZE to the pc. Signed-off-by: Puranjay Mohan <[email protected]> Acked-by: Yonghong Song <[email protected]> Acked-by: Kumar Kartikeya Dwivedi <[email protected]> Acked-by: Xu Kuohai <[email protected]>
BPF streams are only valid for the main programs, to make it easier to access streams from subprogs, introduce main_prog_aux in struct bpf_prog_aux. prog->aux->main_prog_aux = prog->aux, for main programs and prog->aux->main_prog_aux = main_prog->aux, for subprograms. Make bpf_prog_find_from_stack() use the added main_prog_aux to return the mainprog when a subprog is found on the stack. Signed-off-by: Puranjay Mohan <[email protected]>
Begin reporting arena page faults and the faulting address to BPF program's stderr, this patch adds support in the arm64 and x86-64 JITs, support for other archs can be added later. The fault handlers receive the 32 bit address in the arena region so the upper 32 bits of user_vm_start is added to it before printing the address. This is what the user would expect to see as this is what is printed by bpf_printk() is you pass it an address returned by bpf_arena_alloc_pages(); Signed-off-by: Puranjay Mohan <[email protected]> Acked-by: Yonghong Song <[email protected]>
Add __stderr and __stdout to validate the output of BPF streams for bpf selftests. Similar to __xlated, __jited, etc., __stderr/out can be used in the BPF progs to compare a string (regex supported) to the output in the bpf streams. Signed-off-by: Puranjay Mohan <[email protected]>
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Add selftests for testing the reporting of arena page faults through BPF streams. Two new bpf programs are added that read and write to an unmapped arena address and the fault reporting is verified in the userspace through streams. The added bpf programs need to access the user_vm_start in struct bpf_arena, this is done by casting &arena to struct bpf_arena *, but barrier_var() is used on this ptr before accessing ptr->user_vm_start; to stop GCC from issuing an out-of-bound access due to the cast from smaller map struct to larger "struct bpf_arena" Other tests related to streams have been converted to use __stderr in progs/stream.c directly and test_stream_errors() in prog_tests/stream.c has been repurposed to validate the arena fault address printed in the stderr stream. This can't be directly validated using __stderr because the address is dynamic. Signed-off-by: Puranjay Mohan <[email protected]>
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1000090 expired. Closing PR. |
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Pull request for series with
subject: bpf: report arena faults to BPF streams
version: 6
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1000090