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 | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'sys/linux/bpf.txt') diff --git a/sys/linux/bpf.txt b/sys/linux/bpf.txt index eb1c2761b..ae84b0c5e 100644 --- a/sys/linux/bpf.txt +++ b/sys/linux/bpf.txt @@ -400,6 +400,7 @@ bpf_program_ringbuf { initr0 bpf_insn_init_r0 reserve bpf_insn_ringbuf_reserve body array[bpf_insn] + free bpf_insn_ringbuf_submit exit bpf_insn_exit } [packed] @@ -749,6 +750,17 @@ bpf_insn_ringbuf_reserve { insn5 bpf_insn_mov_reg[BPF_REG_0, BPF_REG_9] } +# (bf) r1 = r9 +# (b7) r2 = 0 +# (85) call bpf_ringbuf_submit#322192 +# (bf) r0 = 0 +bpf_insn_ringbuf_submit { + insn1 bpf_insn_mov_reg[BPF_REG_9, BPF_REG_1] + insn2 bpf_insn_mov_imm[BPF_REG_2, 0] + insn3 bpf_insn_call_helper_t[const[BPF_FUNC_ringbuf_submit, int32]] + insn4 bpf_insn_mov_imm[BPF_REG_0, 0] +} + define MAX_BPF_REG __MAX_BPF_REG bpf_obj_pin_map [ -- cgit mrf-deployment