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-rw-r--r--samples/seccomp/bpf-helper.c96
1 files changed, 96 insertions, 0 deletions
diff --git a/samples/seccomp/bpf-helper.c b/samples/seccomp/bpf-helper.c
new file mode 100644
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+++ b/samples/seccomp/bpf-helper.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Seccomp BPF helper functions
+ *
+ * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ * Author: Will Drewry <wad@chromium.org>
+ *
+ * The code may be used by anyone for any purpose,
+ * and can serve as a starting point for developing
+ * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "bpf-helper.h"
+
+int bpf_resolve_jumps(struct bpf_labels *labels,
+ struct sock_filter *filter, size_t count)
+{
+ size_t i;
+
+ if (count < 1 || count > BPF_MAXINSNS)
+ return -1;
+ /*
+ * Walk it once, backwards, to build the label table and do fixups.
+ * Since backward jumps are disallowed by BPF, this is easy.
+ */
+ for (i = 0; i < count; ++i) {
+ size_t offset = count - i - 1;
+ struct sock_filter *instr = &filter[offset];
+ if (instr->code != (BPF_JMP+BPF_JA))
+ continue;
+ switch ((instr->jt<<8)|instr->jf) {
+ case (JUMP_JT<<8)|JUMP_JF:
+ if (labels->labels[instr->k].location == 0xffffffff) {
+ fprintf(stderr, "Unresolved label: '%s'\n",
+ labels->labels[instr->k].label);
+ return 1;
+ }
+ instr->k = labels->labels[instr->k].location -
+ (offset + 1);
+ instr->jt = 0;
+ instr->jf = 0;
+ continue;
+ case (LABEL_JT<<8)|LABEL_JF:
+ if (labels->labels[instr->k].location != 0xffffffff) {
+ fprintf(stderr, "Duplicate label use: '%s'\n",
+ labels->labels[instr->k].label);
+ return 1;
+ }
+ labels->labels[instr->k].location = offset;
+ instr->k = 0; /* fall through */
+ instr->jt = 0;
+ instr->jf = 0;
+ continue;
+ }
+ }
+ return 0;
+}
+
+/* Simple lookup table for labels. */
+__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
+{
+ struct __bpf_label *begin = labels->labels, *end;
+ int id;
+
+ if (labels->count == BPF_LABELS_MAX) {
+ fprintf(stderr, "Too many labels\n");
+ exit(1);
+ }
+ if (labels->count == 0) {
+ begin->label = label;
+ begin->location = 0xffffffff;
+ labels->count++;
+ return 0;
+ }
+ end = begin + labels->count;
+ for (id = 0; begin < end; ++begin, ++id) {
+ if (!strcmp(label, begin->label))
+ return id;
+ }
+ begin->label = label;
+ begin->location = 0xffffffff;
+ labels->count++;
+ return id;
+}
+
+void seccomp_bpf_print(struct sock_filter *filter, size_t count)
+{
+ struct sock_filter *end = filter + count;
+ for ( ; filter < end; ++filter)
+ printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
+ filter->code, filter->jt, filter->jf, filter->k);
+}