Merge tag 'seccomp-v6.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull seccomp fix from Kees Cook:
"This is really a work-around for x86_64 having grown a syscall to
implement uretprobe, which has caused problems since v6.11.

This may change in the future, but for now, this fixes the unintended
seccomp filtering when uretprobe switched away from traps, and does so
with something that should be easy to backport.

- Allow uretprobe on x86_64 to avoid behavioral complications (Eyal
Birger)"

* tag 'seccomp-v6.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
selftests/seccomp: validate uretprobe syscall passes through seccomp
seccomp: passthrough uretprobe systemcall without filtering

kernel/seccomp.c

···
 	if (WARN_ON_ONCE(!fprog))
 		return false;
 
+	/* Our single exception to filtering. */
+#ifdef __NR_uretprobe
+#ifdef SECCOMP_ARCH_COMPAT
+	if (sd->arch == SECCOMP_ARCH_NATIVE)
+#endif
+		if (sd->nr == __NR_uretprobe)
+			return true;
+#endif
+
 	for (pc = 0; pc < fprog->len; pc++) {
 		struct sock_filter *insn = &fprog->filter[pc];
 		u16 code = insn->code;
···
  */
 static const int mode1_syscalls[] = {
 	__NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
+#ifdef __NR_uretprobe
+	__NR_uretprobe,
+#endif
 	-1, /* negative terminated */
 };
 

tools/testing/selftests/seccomp/seccomp_bpf.c

···
 #include <linux/kcmp.h>
 #include <sys/resource.h>
 #include <sys/capability.h>
+#include <linux/perf_event.h>
 
 #include <unistd.h>
 #include <sys/syscall.h>
···
 
 #ifndef PR_SET_PTRACER
 # define PR_SET_PTRACER 0x59616d61
+#endif
+
+#ifndef noinline
+#define noinline __attribute__((noinline))
 #endif
 
 #ifndef PR_SET_NO_NEW_PRIVS
···
 
 	EXPECT_EQ(pid, waitpid(pid, &status, 0));
 	EXPECT_EQ(0, status);
+}
+
+noinline int probed(void)
+{
+	return 1;
+}
+
+static int parse_uint_from_file(const char *file, const char *fmt)
+{
+	int err = -1, ret;
+	FILE *f;
+
+	f = fopen(file, "re");
+	if (f) {
+		err = fscanf(f, fmt, &ret);
+		fclose(f);
+	}
+	return err == 1 ? ret : err;
+}
+
+static int determine_uprobe_perf_type(void)
+{
+	const char *file = "/sys/bus/event_source/devices/uprobe/type";
+
+	return parse_uint_from_file(file, "%d\n");
+}
+
+static int determine_uprobe_retprobe_bit(void)
+{
+	const char *file = "/sys/bus/event_source/devices/uprobe/format/retprobe";
+
+	return parse_uint_from_file(file, "config:%d\n");
+}
+
+static ssize_t get_uprobe_offset(const void *addr)
+{
+	size_t start, base, end;
+	bool found = false;
+	char buf[256];
+	FILE *f;
+
+	f = fopen("/proc/self/maps", "r");
+	if (!f)
+		return -1;
+
+	while (fscanf(f, "%zx-%zx %s %zx %*[^\n]\n", &start, &end, buf, &base) == 4) {
+		if (buf[2] == 'x' && (uintptr_t)addr >= start && (uintptr_t)addr < end) {
+			found = true;
+			break;
+		}
+	}
+	fclose(f);
+	return found ? (uintptr_t)addr - start + base : -1;
+}
+
+FIXTURE(URETPROBE) {
+	int fd;
+};
+
+FIXTURE_VARIANT(URETPROBE) {
+	/*
+	 * All of the URETPROBE behaviors can be tested with either
+	 * uretprobe attached or not
+	 */
+	bool attach;
+};
+
+FIXTURE_VARIANT_ADD(URETPROBE, attached) {
+	.attach = true,
+};
+
+FIXTURE_VARIANT_ADD(URETPROBE, not_attached) {
+	.attach = false,
+};
+
+FIXTURE_SETUP(URETPROBE)
+{
+	const size_t attr_sz = sizeof(struct perf_event_attr);
+	struct perf_event_attr attr;
+	ssize_t offset;
+	int type, bit;
+
+#ifndef __NR_uretprobe
+	SKIP(return, "__NR_uretprobe syscall not defined");
+#endif
+
+	if (!variant->attach)
+		return;
+
+	memset(&attr, 0, attr_sz);
+
+	type = determine_uprobe_perf_type();
+	ASSERT_GE(type, 0);
+	bit = determine_uprobe_retprobe_bit();
+	ASSERT_GE(bit, 0);
+	offset = get_uprobe_offset(probed);
+	ASSERT_GE(offset, 0);
+
+	attr.config |= 1 << bit;
+	attr.size = attr_sz;
+	attr.type = type;
+	attr.config1 = ptr_to_u64("/proc/self/exe");
+	attr.config2 = offset;
+
+	self->fd = syscall(__NR_perf_event_open, &attr,
+			   getpid() /* pid */, -1 /* cpu */, -1 /* group_fd */,
+			   PERF_FLAG_FD_CLOEXEC);
+}
+
+FIXTURE_TEARDOWN(URETPROBE)
+{
+	/* we could call close(self->fd), but we'd need extra filter for
+	 * that and since we are calling _exit right away..
+	 */
+}
+
+static int run_probed_with_filter(struct sock_fprog *prog)
+{
+	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) ||
+	    seccomp(SECCOMP_SET_MODE_FILTER, 0, prog)) {
+		return -1;
+	}
+
+	probed();
+	return 0;
+}
+
+TEST_F(URETPROBE, uretprobe_default_allow)
+{
+	struct sock_filter filter[] = {
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
+	};
+	struct sock_fprog prog = {
+		.len = (unsigned short)ARRAY_SIZE(filter),
+		.filter = filter,
+	};
+
+	ASSERT_EQ(0, run_probed_with_filter(&prog));
+}
+
+TEST_F(URETPROBE, uretprobe_default_block)
+{
+	struct sock_filter filter[] = {
+		BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
+			offsetof(struct seccomp_data, nr)),
+		BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_exit_group, 1, 0),
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_KILL),
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
+	};
+	struct sock_fprog prog = {
+		.len = (unsigned short)ARRAY_SIZE(filter),
+		.filter = filter,
+	};
+
+	ASSERT_EQ(0, run_probed_with_filter(&prog));
+}
+
+TEST_F(URETPROBE, uretprobe_block_uretprobe_syscall)
+{
+	struct sock_filter filter[] = {
+		BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
+			offsetof(struct seccomp_data, nr)),
+#ifdef __NR_uretprobe
+		BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_uretprobe, 0, 1),
+#endif
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_KILL),
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
+	};
+	struct sock_fprog prog = {
+		.len = (unsigned short)ARRAY_SIZE(filter),
+		.filter = filter,
+	};
+
+	ASSERT_EQ(0, run_probed_with_filter(&prog));
+}
+
+TEST_F(URETPROBE, uretprobe_default_block_with_uretprobe_syscall)
+{
+	struct sock_filter filter[] = {
+		BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
+			offsetof(struct seccomp_data, nr)),
+#ifdef __NR_uretprobe
+		BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_uretprobe, 2, 0),
+#endif
+		BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_exit_group, 1, 0),
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_KILL),
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
+	};
+	struct sock_fprog prog = {
+		.len = (unsigned short)ARRAY_SIZE(filter),
+		.filter = filter,
+	};
+
+	ASSERT_EQ(0, run_probed_with_filter(&prog));
 }
 
 /*