[Qemu-devel] [PATCHv2 1/3] seccomp: adding blacklist support

[Eduardo Otubo <otubo@linux.vnet.ibm.com>]

Adding a system call blacklist right before the vcpus starts. This filter is
composed by the system calls that can't be executed after the guests are up.
This list should be refined as the whitelist is, with as much testing as we can
do using virt-test.

Signed-off-by: Eduardo Otubo <otubo@linux.vnet.ibm.com>
---
 include/sysemu/seccomp.h |  5 ++++-
 qemu-seccomp.c           | 57 ++++++++++++++++++++++++++++++++++++++----------
 vl.c                     | 16 +++++++++++++-
 3 files changed, 64 insertions(+), 14 deletions(-)

diff --git a/include/sysemu/seccomp.h b/include/sysemu/seccomp.h
index 1189fa2..551ad12 100644
--- a/include/sysemu/seccomp.h
+++ b/include/sysemu/seccomp.h
@@ -15,8 +15,11 @@
 #ifndef QEMU_SECCOMP_H
 #define QEMU_SECCOMP_H
 
+#define WHITELIST 0
+#define BLACKLIST 1
+
 #include <seccomp.h>
 #include "qemu/osdep.h"
 
-int seccomp_start(void);
+int seccomp_start(int state);
 #endif
diff --git a/qemu-seccomp.c b/qemu-seccomp.c
index 37d38f8..5e85eb5 100644
--- a/qemu-seccomp.c
+++ b/qemu-seccomp.c
@@ -21,7 +21,7 @@ struct QemuSeccompSyscall {
     uint8_t priority;
 };
 
-static const struct QemuSeccompSyscall seccomp_whitelist[] = {
+static const struct QemuSeccompSyscall whitelist[] = {
     { SCMP_SYS(timer_settime), 255 },
     { SCMP_SYS(timer_gettime), 254 },
     { SCMP_SYS(futex), 253 },
@@ -221,32 +221,65 @@ static const struct QemuSeccompSyscall seccomp_whitelist[] = {
     { SCMP_SYS(arch_prctl), 240 }
 };
 
-int seccomp_start(void)
+static const struct QemuSeccompSyscall blacklist[] = {
+    { SCMP_SYS(execve), 255 }
+};
+
+static int process_list(scmp_filter_ctx *ctx,
+                        const struct QemuSeccompSyscall *list,
+                        unsigned int list_size, uint32_t action)
 {
     int rc = 0;
     unsigned int i = 0;
-    scmp_filter_ctx ctx;
 
-    ctx = seccomp_init(SCMP_ACT_KILL);
-    if (ctx == NULL) {
-        goto seccomp_return;
-    }
+    for (i = 0; i < list_size; i++) {
+        rc = seccomp_rule_add(ctx, action, list[i].num, 0);
+        if (rc < 0) {
+            goto seccomp_return;
+        }
 
-    for (i = 0; i < ARRAY_SIZE(seccomp_whitelist); i++) {
-        rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, seccomp_whitelist[i].num, 0);
+        rc = seccomp_syscall_priority(ctx, list[i].num,
+                                      list[i].priority);
         if (rc < 0) {
             goto seccomp_return;
         }
-        rc = seccomp_syscall_priority(ctx, seccomp_whitelist[i].num,
-                                      seccomp_whitelist[i].priority);
+    }
+
+seccomp_return:
+    return rc;
+}
+
+int seccomp_start(int list_type)
+{
+    int rc = 0;
+    scmp_filter_ctx ctx;
+
+    switch (list_type) {
+    case WHITELIST:
+        ctx = seccomp_init(SCMP_ACT_KILL);
+        if (ctx == NULL) {
+            goto seccomp_return;
+        }
+        rc = process_list(ctx, whitelist, ARRAY_SIZE(whitelist), SCMP_ACT_ALLOW);
         if (rc < 0) {
             goto seccomp_return;
         }
+        break;
+    case BLACKLIST:
+        ctx = seccomp_init(SCMP_ACT_ALLOW);
+        if (ctx == NULL) {
+            goto seccomp_return;
+        }
+        rc = process_list(ctx, blacklist, ARRAY_SIZE(blacklist), SCMP_ACT_KILL);
+        break;
+    default:
+        rc = -1;
+        goto seccomp_return;
     }
 
     rc = seccomp_load(ctx);
 
-  seccomp_return:
+seccomp_return:
     seccomp_release(ctx);
     return rc;
 }
diff --git a/vl.c b/vl.c
index b4b119a..02f7486 100644
--- a/vl.c
+++ b/vl.c
@@ -179,6 +179,7 @@ int main(int argc, char **argv)
 #define MAX_VIRTIO_CONSOLES 1
 #define MAX_SCLP_CONSOLES 1
 
+static bool enable_blacklist = false;
 static const char *data_dir[16];
 static int data_dir_idx;
 const char *bios_name = NULL;
@@ -1033,11 +1034,13 @@ static int parse_sandbox(QemuOpts *opts, void *opaque)
     /* FIXME: change this to true for 1.3 */
     if (qemu_opt_get_bool(opts, "enable", false)) {
 #ifdef CONFIG_SECCOMP
-        if (seccomp_start() < 0) {
+        if (seccomp_start(WHITELIST) < 0) {
             qerror_report(ERROR_CLASS_GENERIC_ERROR,
                           "failed to install seccomp syscall filter in the kernel");
             return -1;
         }
+
+        enable_blacklist = true;
 #else
         qerror_report(ERROR_CLASS_GENERIC_ERROR,
                       "sandboxing request but seccomp is not compiled into this build");
@@ -1765,12 +1768,23 @@ void vm_state_notify(int running, RunState state)
     }
 }
 
+static void install_seccomp_blacklist(void)
+{
+    if (enable_blacklist) {
+        if (seccomp_start(BLACKLIST) < 0) {
+            qerror_report(ERROR_CLASS_GENERIC_ERROR,
+                          "failed to install seccomp syscall second level filter in the kernel");
+        }
+    }
+}
+
 void vm_start(void)
 {
     if (!runstate_is_running()) {
         cpu_enable_ticks();
         runstate_set(RUN_STATE_RUNNING);
         vm_state_notify(1, RUN_STATE_RUNNING);
+        install_seccomp_blacklist();
         resume_all_vcpus();
         monitor_protocol_event(QEVENT_RESUME, NULL);
     }
-- 
1.8.3.1