From 64ac6feb8291eb0fe74cf965dd3890625f8f3171 Mon Sep 17 00:00:00 2001 From: Konstantin Ananyev Date: Fri, 17 May 2019 15:09:42 +0100 Subject: [PATCH] bpf: fix pseudo calls for program loaded from ELF clang 6.0 and onwards, for the external function call generates BPF_PSEUDO_CALL instruction: call pseudo +-off -> call another bpf function. More details about that change: https://lwn.net/Articles/741773/ DPDK BPF implementation right now doesn't support multiple BPF functions per module. To overcome that problem, and preserve existing functionality (ability to call allowed by user external functions), bpf_elf_load() clears EBPF_PSEUDO_CALL value. For details how to reproduce the issue: https://bugs.dpdk.org/show_bug.cgi?id=259 Fixes: 5dba93ae5f2d ("bpf: add ability to load eBPF program from ELF object file") Cc: stable@dpdk.org Signed-off-by: Konstantin Ananyev --- lib/librte_bpf/bpf_def.h | 8 ++++++++ lib/librte_bpf/bpf_load_elf.c | 15 +++++++++++++-- lib/librte_bpf/rte_bpf.h | 3 +++ 3 files changed, 24 insertions(+), 2 deletions(-) diff --git a/lib/librte_bpf/bpf_def.h b/lib/librte_bpf/bpf_def.h index c10f3aec46..d39992997a 100644 --- a/lib/librte_bpf/bpf_def.h +++ b/lib/librte_bpf/bpf_def.h @@ -120,6 +120,14 @@ enum { EBPF_REG_NUM, }; +/* + * When EBPF_CALL instruction has src_reg == EBPF_PSEUDO_CALL, + * it should be treated as pseudo-call instruction, where + * imm value contains pc-relative offset to another EBPF function. + * Right now DPDK EBPF library doesn't support it. + */ +#define EBPF_PSEUDO_CALL EBPF_REG_1 + /* * eBPF instruction format */ diff --git a/lib/librte_bpf/bpf_load_elf.c b/lib/librte_bpf/bpf_load_elf.c index 96d3630fe7..926317b6f9 100644 --- a/lib/librte_bpf/bpf_load_elf.c +++ b/lib/librte_bpf/bpf_load_elf.c @@ -77,10 +77,21 @@ resolve_xsym(const char *sn, size_t ofs, struct ebpf_insn *ins, size_t ins_sz, return -ENOENT; /* for function we just need an index in our xsym table */ - if (type == RTE_BPF_XTYPE_FUNC) + if (type == RTE_BPF_XTYPE_FUNC) { + + /* we don't support multiple functions per BPF module, + * so treat EBPF_PSEUDO_CALL to extrernal function + * as an ordinary EBPF_CALL. + */ + if (ins[idx].src_reg == EBPF_PSEUDO_CALL) { + RTE_BPF_LOG(INFO, "%s(%u): " + "EBPF_PSEUDO_CALL to external function: %s\n", + __func__, idx, sn); + ins[idx].src_reg = EBPF_REG_0; + } ins[idx].imm = fidx; /* for variable we need to store its absolute address */ - else { + } else { ins[idx].imm = (uintptr_t)prm->xsym[fidx].var.val; ins[idx + 1].imm = (uint64_t)(uintptr_t)prm->xsym[fidx].var.val >> 32; diff --git a/lib/librte_bpf/rte_bpf.h b/lib/librte_bpf/rte_bpf.h index ab92af8fe0..c8b9601764 100644 --- a/lib/librte_bpf/rte_bpf.h +++ b/lib/librte_bpf/rte_bpf.h @@ -134,6 +134,9 @@ rte_bpf_load(const struct rte_bpf_prm *prm); /** * Create a new eBPF execution context and load BPF code from given ELF * file into it. + * Note that if the function will encounter EBPF_PSEUDO_CALL instruction + * that references external symbol, it will treat is as standard BPF_CALL + * to the external helper function. * * @param prm * Parameters used to create and initialise the BPF execution context. -- 2.20.1