From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sandipan Das Subject: [PATCH bpf v2 1/6] bpf: support 64-bit offsets for bpf function calls Date: Fri, 18 May 2018 18:20:34 +0530 Message-ID: <20180518125039.6500-2-sandipan@linux.vnet.ibm.com> References: <20180518125039.6500-1-sandipan@linux.vnet.ibm.com> Cc: netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, naveen.n.rao@linux.vnet.ibm.com, mpe@ellerman.id.au, jakub.kicinski@netronome.com To: ast@kernel.org, daniel@iogearbox.net Return-path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:36688 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751452AbeERMuv (ORCPT ); Fri, 18 May 2018 08:50:51 -0400 Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w4ICiTPG047475 for ; Fri, 18 May 2018 08:50:50 -0400 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0b-001b2d01.pphosted.com with ESMTP id 2j1vdkqkd6-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Fri, 18 May 2018 08:50:49 -0400 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 18 May 2018 13:50:47 +0100 In-Reply-To: <20180518125039.6500-1-sandipan@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: The imm field of a bpf instruction is a signed 32-bit integer. For JIT bpf-to-bpf function calls, it stores the offset of the start address of the callee's JITed image from __bpf_call_base. For some architectures, such as powerpc64, this offset may be as large as 64 bits and cannot be accomodated in the imm field without truncation. We resolve this by: [1] Additionally using the auxillary data of each function to keep a list of start addresses of the JITed images for all functions determined by the verifier. [2] Retaining the subprog id inside the off field of the call instructions and using it to index into the list mentioned above and lookup the callee's address. To make sure that the existing JIT compilers continue to work without requiring changes, we keep the imm field as it is. Signed-off-by: Sandipan Das --- kernel/bpf/verifier.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a9e4b1372da6..6c56cce9c4e3 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5383,11 +5383,24 @@ static int jit_subprogs(struct bpf_verifier_env *env) insn->src_reg != BPF_PSEUDO_CALL) continue; subprog = insn->off; - insn->off = 0; insn->imm = (u64 (*)(u64, u64, u64, u64, u64)) func[subprog]->bpf_func - __bpf_call_base; } + + /* we use the aux data to keep a list of the start addresses + * of the JITed images for each function in the program + * + * for some architectures, such as powerpc64, the imm field + * might not be large enough to hold the offset of the start + * address of the callee's JITed image from __bpf_call_base + * + * in such cases, we can lookup the start address of a callee + * by using its subprog id, available from the off field of + * the call instruction, as an index for this list + */ + func[i]->aux->func = func; + func[i]->aux->func_cnt = env->subprog_cnt + 1; } for (i = 0; i < env->subprog_cnt; i++) { old_bpf_func = func[i]->bpf_func; -- 2.14.3