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authorJiong Wang <jiong.wang@netronome.com>2019-05-24 23:25:15 +0100
committerAlexei Starovoitov <ast@kernel.org>2019-05-24 18:58:37 -0700
commita4b1d3c1ddf6cb441187b6c130a473c16a05a356 (patch)
treefa54a491f3095c32cad767328a643211f6990951 /kernel
parent7d134041a89610ae552501fc88652805addcdee4 (diff)
bpf: verifier: insert zero extension according to analysis result
After previous patches, verifier will mark a insn if it really needs zero extension on dst_reg. It is then for back-ends to decide how to use such information to eliminate unnecessary zero extension code-gen during JIT compilation. One approach is verifier insert explicit zero extension for those insns that need zero extension in a generic way, JIT back-ends then do not generate zero extension for sub-register write at default. However, only those back-ends which do not have hardware zero extension want this optimization. Back-ends like x86_64 and AArch64 have hardware zero extension support that the insertion should be disabled. This patch introduces new target hook "bpf_jit_needs_zext" which returns false at default, meaning verifier zero extension insertion is disabled at default. A back-end could override this hook to return true if it doesn't have hardware support and want verifier insert zero extension explicitly. Offload targets do not use this native target hook, instead, they could get the optimization results using bpf_prog_offload_ops.finalize. NOTE: arches could have diversified features, it is possible for one arch to have hardware zero extension support for some sub-register write insns but not for all. For example, PowerPC, SPARC have zero extended loads, but not for alu32. So when verifier zero extension insertion enabled, these JIT back-ends need to peephole insns to remove those zero extension inserted for insn that actually has hardware zero extension support. The peephole could be as simple as looking the next insn, if it is a special zero extension insn then it is safe to eliminate it if the current insn has hardware zero extension support. Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com> Signed-off-by: Jiong Wang <jiong.wang@netronome.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/core.c9
-rw-r--r--kernel/bpf/verifier.c41
2 files changed, 50 insertions, 0 deletions
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 242a643af82f..3675b19ecb90 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2090,6 +2090,15 @@ bool __weak bpf_helper_changes_pkt_data(void *func)
return false;
}
+/* Return TRUE if the JIT backend wants verifier to enable sub-register usage
+ * analysis code and wants explicit zero extension inserted by verifier.
+ * Otherwise, return FALSE.
+ */
+bool __weak bpf_jit_needs_zext(void)
+{
+ return false;
+}
+
/* To execute LD_ABS/LD_IND instructions __bpf_prog_run() may call
* skb_copy_bits(), so provide a weak definition of it for NET-less config.
*/
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a6af3166acae..d4394a84b9eb 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7640,6 +7640,38 @@ static int opt_remove_nops(struct bpf_verifier_env *env)
return 0;
}
+static int opt_subreg_zext_lo32(struct bpf_verifier_env *env)
+{
+ struct bpf_insn_aux_data *aux = env->insn_aux_data;
+ struct bpf_insn *insns = env->prog->insnsi;
+ int i, delta = 0, len = env->prog->len;
+ struct bpf_insn zext_patch[2];
+ struct bpf_prog *new_prog;
+
+ zext_patch[1] = BPF_ZEXT_REG(0);
+ for (i = 0; i < len; i++) {
+ int adj_idx = i + delta;
+ struct bpf_insn insn;
+
+ if (!aux[adj_idx].zext_dst)
+ continue;
+
+ insn = insns[adj_idx];
+ zext_patch[0] = insn;
+ zext_patch[1].dst_reg = insn.dst_reg;
+ zext_patch[1].src_reg = insn.dst_reg;
+ new_prog = bpf_patch_insn_data(env, adj_idx, zext_patch, 2);
+ if (!new_prog)
+ return -ENOMEM;
+ env->prog = new_prog;
+ insns = new_prog->insnsi;
+ aux = env->insn_aux_data;
+ delta += 2;
+ }
+
+ return 0;
+}
+
/* convert load instructions that access fields of a context type into a
* sequence of instructions that access fields of the underlying structure:
* struct __sk_buff -> struct sk_buff
@@ -8490,6 +8522,15 @@ skip_full_check:
if (ret == 0)
ret = fixup_bpf_calls(env);
+ /* do 32-bit optimization after insn patching has done so those patched
+ * insns could be handled correctly.
+ */
+ if (ret == 0 && bpf_jit_needs_zext() &&
+ !bpf_prog_is_dev_bound(env->prog->aux)) {
+ ret = opt_subreg_zext_lo32(env);
+ env->prog->aux->verifier_zext = !ret;
+ }
+
if (ret == 0)
ret = fixup_call_args(env);