all: add seccomp_precompute() functionality

This patch adds a seccomp_precompute() API to precompute the seccomp
filter prior to calling seccomp_load() or similar functions.  Not
only does this improve the performance of seccomp_load(), it ensures
that seccomp_load() is async-signal-safe if no additional changes
have been made since the filter was precomputed.

Python bindings, test, and manpage updates are included in this
patch.

One minor side effect of this change is that seccomp_export_bpf_mem()
now always return the length of the filter in the "len" function
parameter, even in cases where the passed buffer is too small.
Arguably seccomp_export_bpf_mem() should have always behaved this
way.

Signed-off-by: Paul Moore <paul@paul-moore.com>

6 files changed, 101 insertions, 13 deletions

diff --git a/src/api.c b/src/api.c
index 423a1c5..9c2f64a 100644
--- a/src/api.c
+++ b/src/api.c
@@ -2,6 +2,7 @@
  * Seccomp Library API
  *
  * Copyright (c) 2012,2013 Red Hat <pmoore@redhat.com>
+ * Copyright (c) 2022 Microsoft Corporation <paulmoore@microsoft.com>
  * Author: Paul Moore <paul@paul-moore.com>
  */
 
@@ -723,11 +724,11 @@ API int seccomp_export_bpf(const scmp_filter_ctx ctx, int fd)
 		return _rc_filter(-EINVAL);
 	col = (struct db_filter_col *)ctx;
 
-	rc = gen_bpf_generate(col, &program);
+	rc = db_col_precompute(col);
 	if (rc < 0)
 		return _rc_filter(rc);
+	program = col->prgm_bpf;
 	rc = write(fd, program->blks, BPF_PGM_SIZE(program));
-	gen_bpf_release(program);
 	if (rc < 0)
 		return _rc_filter_sys(col, -errno);
 
@@ -739,7 +740,6 @@ API int seccomp_export_bpf_mem(const scmp_filter_ctx ctx, void *buf,
 			       size_t *len)
 {
 	int rc;
-	size_t buf_len;
 	struct db_filter_col *col;
 	struct bpf_program *program;
 
@@ -747,21 +747,31 @@ API int seccomp_export_bpf_mem(const scmp_filter_ctx ctx, void *buf,
 		return _rc_filter(-EINVAL);
 	col = (struct db_filter_col *)ctx;
 
-	rc = gen_bpf_generate(col, &program);
+	rc = db_col_precompute(col);
 	if (rc < 0)
 		return _rc_filter(rc);
-	buf_len = *len;
-	*len = BPF_PGM_SIZE(program);
+	program = col->prgm_bpf;
 
-	rc = 0;
 	if (buf) {
 		/* If we have a big enough buffer, write the program. */
-		if (*len > buf_len)
+		if (BPF_PGM_SIZE(program) > *len)
 			rc = _rc_filter(-ERANGE);
 		else
 			memcpy(buf, program->blks, *len);
 	}
-	gen_bpf_release(program);
+	*len = BPF_PGM_SIZE(program);
 
 	return rc;
 }
+
+/* NOTE - function header comment in include/seccomp.h */
+API int seccomp_precompute(const scmp_filter_ctx ctx)
+{
+	struct db_filter_col *col;
+
+	if (_ctx_valid(ctx))
+		return _rc_filter(-EINVAL);
+	col = (struct db_filter_col *)ctx;
+
+	return _rc_filter(db_col_precompute(col));
+}
diff --git a/src/db.c b/src/db.c
index 3d9585a..6d81874 100644
--- a/src/db.c
+++ b/src/db.c
@@ -3,6 +3,7 @@
  *
  * Copyright (c) 2012,2016,2018 Red Hat <pmoore@redhat.com>
  * Copyright (c) 2019 Cisco Systems, Inc. <pmoore2@cisco.com>
+ * Copyright (c) 2022 Microsoft Corporation <paulmoore@microsoft.com>
  * Author: Paul Moore <paul@paul-moore.com>
  */
 
@@ -1098,6 +1099,9 @@ int db_col_reset(struct db_filter_col *col, uint32_t def_action)
 		free(snap);
 	}
 
+	/* reset the precomputed programs */
+	db_col_precompute_reset(col);
+
 	return 0;
 }
 
@@ -1162,6 +1166,9 @@ void db_col_release(struct db_filter_col *col)
 		free(col->filters);
 	col->filters = NULL;
 
+	/* free any precompute */
+	db_col_precompute_reset(col);
+
 	/* free the collection */
 	free(col);
 }
@@ -1250,6 +1257,9 @@ int db_col_merge(struct db_filter_col *col_dst, struct db_filter_col *col_src)
 		col_dst->filter_cnt++;
 	}
 
+	/* reset the precompute */
+	db_col_precompute_reset(col_dst);
+
 	/* free the source */
 	col_src->filter_cnt = 0;
 	db_col_release(col_src);
@@ -1373,6 +1383,7 @@ int db_col_attr_set(struct db_filter_col *col,
 			col->attr.act_badarch = value;
 		else
 			return -EINVAL;
+		db_col_precompute_reset(col);
 		break;
 	case SCMP_FLTATR_CTL_NNP:
 		col->attr.nnp_enable = (value ? 1 : 0);
@@ -1394,6 +1405,7 @@ int db_col_attr_set(struct db_filter_col *col,
 		break;
 	case SCMP_FLTATR_API_TSKIP:
 		col->attr.api_tskip = (value ? 1 : 0);
+		db_col_precompute_reset(col);
 		break;
 	case SCMP_FLTATR_CTL_LOG:
 		rc = sys_chk_seccomp_flag(SECCOMP_FILTER_FLAG_LOG);
@@ -1427,6 +1439,7 @@ int db_col_attr_set(struct db_filter_col *col,
 			rc = -EOPNOTSUPP;
 			break;
 		}
+		db_col_precompute_reset(col);
 		break;
 	case SCMP_FLTATR_API_SYSRAWRC:
 		col->attr.api_sysrawrc = (value ? 1 : 0);
@@ -1460,6 +1473,8 @@ int db_col_db_new(struct db_filter_col *col, const struct arch_def *arch)
 	rc = db_col_db_add(col, db);
 	if (rc < 0)
 		_db_release(db);
+	else
+		db_col_precompute_reset(col);
 
 	return rc;
 }
@@ -1540,6 +1555,8 @@ int db_col_db_remove(struct db_filter_col *col, uint32_t arch_token)
 		col->endian = 0;
 	}
 
+	db_col_precompute_reset(col);
+
 	return 0;
 }
 
@@ -2233,6 +2250,9 @@ priority_failure:
 			rc = rc_tmp;
 	}
 
+	if (rc == 0)
+		db_col_precompute_reset(col);
+
 	return rc;
 }
 
@@ -2377,8 +2397,11 @@ add_arch_fail:
 
 add_return:
 	/* update the misc state */
-	if (rc == 0 && action == SCMP_ACT_NOTIFY)
-		col->notify_used = true;
+	if (rc == 0) {
+		if (action == SCMP_ACT_NOTIFY)
+			col->notify_used = true;
+		db_col_precompute_reset(col);
+	}
 	if (chain != NULL)
 		free(chain);
 	return rc;
@@ -2501,6 +2524,9 @@ void db_col_transaction_abort(struct db_filter_col *col)
 	for (iter = 0; iter < filter_cnt; iter++)
 		_db_release(filters[iter]);
 	free(filters);
+
+	/* free any precompute */
+	db_col_precompute_reset(col);
 }
 
 /**
@@ -2618,3 +2644,33 @@ shadow_err:
 	_db_snap_release(snap);
 	return;
 }
+
+/**
+ * Precompute the seccomp filters
+ * @param col the filter collection
+ *
+ * This function precomputes the seccomp filters before they are needed,
+ * returns zero on success, negative values on error.
+ *
+ */
+int db_col_precompute(struct db_filter_col *col)
+{
+	if (!col->prgm_bpf)
+		return gen_bpf_generate(col, &col->prgm_bpf);
+	return 0;
+}
+
+/**
+ * Free any precomputed filter programs
+ * @param col the filter collection
+ *
+ * This function releases any precomputed filter programs.
+ */
+void db_col_precompute_reset(struct db_filter_col *col)
+{
+	if (!col->prgm_bpf)
+		return;
+
+	gen_bpf_release(col->prgm_bpf);
+	col->prgm_bpf = NULL;
+}
diff --git a/src/db.h b/src/db.h
index 765c607..9a41427 100644
--- a/src/db.h
+++ b/src/db.h
@@ -2,6 +2,7 @@
  * Enhanced Seccomp Filter DB
  *
  * Copyright (c) 2012,2016 Red Hat <pmoore@redhat.com>
+ * Copyright (c) 2022 Microsoft Corporation <paulmoore@microsoft.com>
  * Author: Paul Moore <paul@paul-moore.com>
  */
 
@@ -28,6 +29,7 @@
 #include <seccomp.h>
 
 #include "arch.h"
+#include "gen_bpf.h"
 
 /* XXX - need to provide doxygen comments for the types here */
 
@@ -162,6 +164,9 @@ struct db_filter_col {
 
 	/* userspace notification */
 	bool notify_used;
+
+	/* precomputed programs */
+	struct bpf_program *prgm_bpf;
 };
 
 /**
@@ -212,6 +217,9 @@ int db_col_transaction_start(struct db_filter_col *col);
 void db_col_transaction_abort(struct db_filter_col *col);
 void db_col_transaction_commit(struct db_filter_col *col);
 
+int db_col_precompute(struct db_filter_col *col);
+void db_col_precompute_reset(struct db_filter_col *col);
+
 int db_rule_add(struct db_filter *db, const struct db_api_rule_list *rule);
 
 #endif
diff --git a/src/python/libseccomp.pxd b/src/python/libseccomp.pxd
index 6175c8a..9589cfe 100644
--- a/src/python/libseccomp.pxd
+++ b/src/python/libseccomp.pxd
@@ -170,5 +170,7 @@ cdef extern from "seccomp.h":
     int seccomp_export_bpf_mem(const scmp_filter_ctx ctx, void *buf,
                                size_t *len)
 
+    int seccomp_precompute(const scmp_filter_ctx ctx)
+
 # kate: syntax python;
 # kate: indent-mode python; space-indent on; indent-width 4; mixedindent off;
diff --git a/src/python/seccomp.pyx b/src/python/seccomp.pyx
index 3551aac..1f58517 100644
--- a/src/python/seccomp.pyx
+++ b/src/python/seccomp.pyx
@@ -1069,5 +1069,17 @@ cdef class SyscallFilter:
             raise RuntimeError(str.format("Library error (errno = {0})", rc))
         return program
 
+    def precompute(self):
+        """ Precompute the seccomp filter.
+
+        Description:
+        Precompute the seccomp filter and store it internally for future use,
+        speeding up filter loads and other functions which require the
+        generated filter.
+        """
+        rc = libseccomp.seccomp_precompute(self._ctx)
+        if rc != 0:
+            raise RuntimeError(str.format("Library error (errno = {0})", rc))
+
 # kate: syntax python;
 # kate: indent-mode python; space-indent on; indent-width 4; mixedindent off;
diff --git a/src/system.c b/src/system.c
index ae445bf..94e0405 100644
--- a/src/system.c
+++ b/src/system.c
@@ -360,9 +360,10 @@ int sys_filter_load(struct db_filter_col *col, bool rawrc)
 	bool listener_req;
 	struct bpf_program *prgm = NULL;
 
-	rc = gen_bpf_generate(col, &prgm);
+	rc = db_col_precompute(col);
 	if (rc < 0)
 		return rc;
+	prgm = col->prgm_bpf;
 
 	/* attempt to set NO_NEW_PRIVS */
 	if (col->attr.nnp_enable) {
@@ -417,7 +418,6 @@ int sys_filter_load(struct db_filter_col *col, bool rawrc)
 
 filter_load_out:
 	/* cleanup and return */
-	gen_bpf_release(prgm);
 	if (rc == -ESRCH)
 		return -ESRCH;
 	if (rc < 0)