From ce85d4183896b735669c38b5f6c441d4f31db1ca Mon Sep 17 00:00:00 2001 From: Paul Chaignon Date: Mon, 6 Nov 2023 23:02:24 +0100 Subject: sys/linux: describe call to BPF helper bpf_ringbuf_submit This helper has the verifier prototype: .ret_type = RET_VOID, .arg1_type = ARG_PTR_TO_RINGBUF_MEM | OBJ_RELEASE, .arg2_type = ARG_ANYTHING, We therefore need to pass the pointer retrieved with bpf_ringbuf_reserve via R2. We saved that pointer to R9 so we can retrieve it from there. Since bpf_ringbuf_submit doesn't return anything, we need to write something in R0 before we exit the program. Our BPF program now looks like: u64 *e; e = bpf_ringbuf_reserve(&rb, sizeof(*e), 0); [...] bpf_ringbuf_submit(e, 0); return 0; It will still fail, but with EACCES instead of EINVAL, due to the following verifier error: 0: R1=ctx(off=0,imm=0) R10=fp0 0: (18) r0 = 0x0 ; R0_w=0 2: (18) r1 = 0xffff984f66f93600 ; R1_w=map_ptr(off=0,ks=0,vs=0,imm=0) 4: (b7) r2 = 20 ; R2_w=20 5: (b7) r3 = 0 ; R3_w=0 6: (85) call bpf_ringbuf_reserve#131 ; R0_w=ringbuf_mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) refs=2 7: (bf) r9 = r0 ; R0_w=ringbuf_mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R9_w=ringbuf_mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) refs=2 8: (bf) r1 = r9 ; R1_w=ringbuf_mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R9_w=ringbuf_mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) refs=2 9: (b7) r2 = 0 ; R2_w=0 refs=2 10: (85) call bpf_ringbuf_submit#132 R1 type=ringbuf_mem_or_null expected=ringbuf_mem In short, we didn't check that the pointer returned by bpf_ringbug_reserve isn't null. Signed-off-by: Paul Chaignon --- sys/linux/bpf.txt.const | 1 + 1 file changed, 1 insertion(+) (limited to 'sys/linux/bpf.txt.const') diff --git a/sys/linux/bpf.txt.const b/sys/linux/bpf.txt.const index 8091b3944..c0ee42926 100644 --- a/sys/linux/bpf.txt.const +++ b/sys/linux/bpf.txt.const @@ -67,6 +67,7 @@ BPF_EXIT0 = 9 BPF_FLOW_DISSECTOR = 17 BPF_FUNC_INFO_SIZE = 8 BPF_FUNC_ringbuf_reserve = 131 +BPF_FUNC_ringbuf_submit = 132 BPF_FUNC_snprintf = 165 BPF_FUNC_tail_call = 12 BPF_FUNC_trace_printk = 6 -- cgit mrf-deployment