[PATCH 6/6] [DEBUG] seccomp: Report bitmap coverage ranges

[Kees Cook <keescook@xxxxxxxxxxxx>]

This is what I've been using to explore actual bitmap results for
real-world filters...

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 kernel/seccomp.c | 115 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 9921f6f39d12..1a0595d7f8ef 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -835,6 +835,85 @@ static void seccomp_update_bitmap(struct seccomp_filter *filter,
 	}
 }
 
+static void __report_bitmap(const char *arch, u32 ret, int start, int finish)
+{
+	int gap;
+	char *name;
+
+	if (finish == -1)
+		return;
+
+	switch (ret) {
+	case UINT_MAX:
+		name = "filter";
+		break;
+	case SECCOMP_RET_ALLOW:
+		name = "SECCOMP_RET_ALLOW";
+		break;
+	case SECCOMP_RET_KILL_PROCESS:
+		name = "SECCOMP_RET_KILL_PROCESS";
+		break;
+	case SECCOMP_RET_KILL_THREAD:
+		name = "SECCOMP_RET_KILL_THREAD";
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		name = "unknown";
+		break;
+	}
+
+	gap = 0;
+	if (start < 100)
+		gap++;
+	if (start < 10)
+		gap++;
+	if (finish < 100)
+		gap++;
+	if (finish < 10)
+		gap++;
+
+	if (start == finish)
+		pr_info("%s     %3d: %s\n", arch, start, name);
+	else if (start + 1 == finish)
+		pr_info("%s %*s%d,%d: %s\n", arch, gap, "", start, finish, name);
+	else
+		pr_info("%s %*s%d-%d: %s\n", arch, gap, "", start, finish, name);
+}
+
+static void report_bitmap(struct seccomp_bitmaps *bitmaps, const char *arch)
+{
+	u32 nr;
+	int start = 0, finish = -1;
+	u32 ret = UINT_MAX;
+	struct report_states {
+		unsigned long *bitmap;
+		u32 ret;
+	} states[] = {
+		{ .bitmap = bitmaps->allow,	   .ret = SECCOMP_RET_ALLOW, },
+		{ .bitmap = bitmaps->kill_process, .ret = SECCOMP_RET_KILL_PROCESS, },
+		{ .bitmap = bitmaps->kill_thread,  .ret = SECCOMP_RET_KILL_THREAD, },
+		{ .bitmap = NULL,		   .ret = UINT_MAX, },
+	};
+
+	for (nr = 0; nr < NR_syscalls; nr++) {
+		int i;
+
+		for (i = 0; i < ARRAY_SIZE(states); i++) {
+			if (!states[i].bitmap || test_bit(nr, states[i].bitmap)) {
+				if (ret != states[i].ret) {
+					__report_bitmap(arch, ret, start, finish);
+					ret = states[i].ret;
+					start = nr;
+				}
+				finish = nr;
+				break;
+			}
+		}
+	}
+	if (start != nr)
+		__report_bitmap(arch, ret, start, finish);
+}
+
 static void seccomp_update_bitmaps(struct seccomp_filter *filter,
 				   void *pagepair)
 {
@@ -849,6 +928,23 @@ static void seccomp_update_bitmaps(struct seccomp_filter *filter,
 			      SECCOMP_MULTIPLEXED_SYSCALL_TABLE_MASK,
 			      &current->seccomp.multiplex);
 #endif
+	if (strncmp(current->comm, "test-", 5) == 0 ||
+	    strcmp(current->comm, "seccomp_bpf") == 0 ||
+	    /*
+	     * Why are systemd's process names head-truncated to 8 bytes
+	     * and wrapped in parens!?
+	     */
+	    (current->comm[0] == '(' && strrchr(current->comm, ')') != NULL)) {
+		pr_info("reporting syscall bitmap usage for %d (%s):\n",
+			task_pid_nr(current), current->comm);
+		report_bitmap(&current->seccomp.native, "native");
+#ifdef CONFIG_COMPAT
+		report_bitmap(&current->seccomp.compat, "compat");
+#endif
+#ifdef SECCOMP_MULTIPLEXED_SYSCALL_TABLE_ARCH
+		report_bitmap(&current->seccomp.multiplex, "multiplex");
+#endif
+	}
 }
 #else
 static void seccomp_update_bitmaps(struct seccomp_filter *filter,
@@ -908,6 +1004,10 @@ static long seccomp_attach_filter(unsigned int flags,
 	filter->prev = current->seccomp.filter;
 	current->seccomp.filter = filter;
 	atomic_inc(&current->seccomp.filter_count);
+	if (atomic_read(&current->seccomp.filter_count) > 10)
+		pr_info("%d filters: %d (%s)\n",
+			atomic_read(&current->seccomp.filter_count),
+			task_pid_nr(current), current->comm);
 
 	/* Evaluate filter for new known-outcome syscalls */
 	seccomp_update_bitmaps(filter, pagepair);
@@ -2419,6 +2519,21 @@ static int __init seccomp_sysctl_init(void)
 		pr_warn("sysctl registration failed\n");
 	else
 		kmemleak_not_leak(hdr);
+#ifndef SECCOMP_ARCH
+	pr_info("arch lacks support for constant action bitmaps\n");
+#else
+	pr_info("NR_syscalls: %d\n", NR_syscalls);
+	pr_info("arch: 0x%x\n", SECCOMP_ARCH);
+#ifdef CONFIG_COMPAT
+	pr_info("compat arch: 0x%x\n", SECCOMP_ARCH_COMPAT);
+#endif
+#ifdef SECCOMP_MULTIPLEXED_SYSCALL_TABLE_ARCH
+	pr_info("multiplex arch: 0x%x (mask: 0x%x)\n",
+		SECCOMP_MULTIPLEXED_SYSCALL_TABLE_ARCH,
+		SECCOMP_MULTIPLEXED_SYSCALL_TABLE_MASK);
+#endif
+#endif
+	pr_info("sizeof(struct seccomp_bitmaps): %zu\n", sizeof(struct seccomp_bitmaps));
 
 	return 0;
 }
-- 
2.25.1