[LibOS] Introduce sys.fds.limit manifest option

This manifest option allows to modify the original `RLIMIT_NOFILE`
resource limit. There is *no* way to propagate this limit from the host;
this is a deliberate design choice.

Signed-off-by: Dmitrii Kuvaiskii <[email protected]>

Documentation/devel/features.md

@@ -2963,7 +2963,8 @@ current process. The following resources are supported:
 - `RLIMIT_CORE` -- dummy, zero by default
 - `RLIMIT_RSS` -- dummy, no limit by default
 - `RLIMIT_NPROC` -- dummy, no limit by default
-- `RLIMIT_NOFILE` -- implemented, default soft limit is 900, default hard limit is 65K
+- `RLIMIT_NOFILE` -- implemented, equal to `sys.fds.limit` {ref}`manifest option <sys-fds-limit>` by
+  default
 - `RLIMIT_MEMLOCK` -- dummy, no limit by default
 - `RLIMIT_AS` -- dummy, no limit by default
 - `RLIMIT_LOCKS` -- dummy, no limit by default

Documentation/manifest-syntax.rst

@@ -308,6 +308,21 @@ may improve performance for certain workloads but may also generate
 ``SIGSEGV/SIGBUS`` exceptions for some applications that specifically use
 invalid pointers (though this is not expected for most real-world applications).
 
+.. _sys-fds-limit:
+
+Limit on open file descriptors
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+::
+
+    sys.fds.limit = [NUM]
+    (default: 900)
+
+This specifies the maximum number of open file descriptors in the Gramine
+process. More specifically, this option sets the ``RLIMIT_NOFILE`` resource
+limit: it specifies a value one greater than the maximum file descriptor number
+that can be opened by the Gramine process.
+
 .. _stack-size:
 
 Stack size

libos/src/bookkeep/libos_handle.c

@@ -146,10 +146,33 @@ int init_handle(void) {
     if (!create_lock(&handle_mgr_lock)) {
         return -ENOMEM;
     }
+
     handle_mgr = create_mem_mgr(init_align_up(HANDLE_MGR_ALLOC));
     if (!handle_mgr) {
         return -ENOMEM;
     }
+
+    /* after fork, in the new child process, `libos_init` is run, hence this function too - but
+     * forked process will get its RLIMIT_NOFILE from the checkpoint */
+    assert(g_pal_public_state);
+    if (g_pal_public_state->parent_process)
+        return 0;
+
+    assert(g_manifest_root);
+    int64_t fds_limit_init64;
+    int ret = toml_int_in(g_manifest_root, "sys.fds.limit",
+                          /*defaultval=*/get_rlimit_cur(RLIMIT_NOFILE),
+                          &fds_limit_init64);
+    if (ret < 0) {
+        log_error("Cannot parse 'sys.fds.limit'");
+        return -EINVAL;
+    }
+    if (fds_limit_init64 < 0) {
+        log_error("'sys.fds.limit' is negative (%ld)", fds_limit_init64);
+        return -EINVAL;
+    }
+    set_rlimit_cur(RLIMIT_NOFILE, (uint64_t)fds_limit_init64);
+
     return 0;
 }
 

libos/src/sys/libos_getrlimit.c

@@ -16,7 +16,17 @@
 #include "linux_abi/sysinfo.h"
 
 /*
- * TODO: implement actual limitation on each resource.
+ * The only resource limits that affect internal Gramine logic are:
+ *
+ *   - RLIMIT_DATA:   initially equal to `sys.brk.max_size` manifest option, affects `brk()` system
+ *                    call
+ *   - RLIMIT_STACK:  initially equal to `sys.stack.size` manifest option, but updating this limit
+ *                    does *not* affect the max stack size of the main thread for processes which
+ *                    are already running
+ *   - RLIMIT_NOFILE: initially equal to `sys.fds.limit` manifest option, affects system calls that
+ *                    create new file descriptors, e.g. open(), dup(), pipe(), etc.
+ *
+ * FIXME: implement actual limitation on each resource?
  *
  * The current behavor(i.e. sys_stack_size, brk_max_size) may be subject
  * to be fixed.

libos/test/regression/meson.build

@@ -102,6 +102,7 @@ tests = {
     'readdir': {},
     'rename_unlink': {},
     'rename_unlink_fchown': {},
+    'rlimit_nofile': {},
     'run_test': {
         'include_directories': include_directories(
             # for `gramine_entry_api.h`

libos/test/regression/rlimit_nofile.c

@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/* Copyright (C) 2024 Intel Corporation */
+
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/resource.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "common.h"
+
+int main(void) {
+    struct rlimit rlim;
+
+    int dev_null_fd = CHECK(open("/dev/null", O_WRONLY, 0666));
+
+    CHECK(getrlimit(RLIMIT_NOFILE, &rlim));
+    printf("old RLIMIT_NOFILE soft limit: %d\n", (int)rlim.rlim_cur);
+    int old_lim = (int)rlim.rlim_cur;
+
+    /* make sure we can increase the current soft limit */
+    if (old_lim <= 0 || old_lim >= (int)rlim.rlim_max)
+        CHECK(-1);
+
+    int good_dup_fd = dup2(dev_null_fd, old_lim - 1);
+    CHECK(good_dup_fd);
+    printf("(before setrlimit) opened fd: %d\n", good_dup_fd);
+    CHECK(close(good_dup_fd));
+
+    int fail_dup_fd = dup2(dev_null_fd, old_lim);
+    if (fail_dup_fd != -1 || errno != EBADF)
+        CHECK(-1);
+
+    rlim.rlim_cur++;
+    CHECK(setrlimit(RLIMIT_NOFILE, &rlim));
+    printf("new RLIMIT_NOFILE soft limit: %d\n", (int)rlim.rlim_cur);
+
+    fflush(stdout);
+
+    int pid = CHECK(fork());
+    if (pid == 0) {
+        /* verify that NOFILE limit is correctly migrated to the child process */
+        good_dup_fd = dup2(dev_null_fd, old_lim);
+        CHECK(good_dup_fd);
+        printf("(in child, after setrlimit) opened fd: %d\n", good_dup_fd);
+        exit(0);
+    } else {
+        int status = 0;
+        CHECK(wait(&status));
+        if (!WIFEXITED(status) || WEXITSTATUS(status))
+            errx(1, "child wait status: %#x", status);
+    }
+
+    good_dup_fd = dup2(dev_null_fd, old_lim);
+    CHECK(good_dup_fd);
+    printf("(after setrlimit) opened fd: %d\n", good_dup_fd);
+    CHECK(close(good_dup_fd));
+
+    CHECK(close(dev_null_fd));
+    puts("TEST OK");
+    return 0;
+}

libos/test/regression/rlimit_nofile_4k.manifest.template

@@ -0,0 +1,22 @@
+{% set entrypoint = "rlimit_nofile" -%}
+
+libos.entrypoint = "{{ entrypoint }}"
+
+loader.env.LD_LIBRARY_PATH = "/lib"
+
+fs.mounts = [
+  { path = "/lib", uri = "file:{{ gramine.runtimedir(libc) }}" },
+  { path = "/{{ entrypoint }}", uri = "file:{{ binary_dir }}/{{ entrypoint }}" },
+]
+
+sys.fds.limit = 4096
+
+sgx.max_threads = {{ '1' if env.get('EDMM', '0') == '1' else '4' }}
+sgx.debug = true
+sgx.edmm_enable = {{ 'true' if env.get('EDMM', '0') == '1' else 'false' }}
+sgx.use_exinfo = {{ 'true' if env.get('EDMM', '0') == '1' else 'false' }}
+
+sgx.trusted_files = [
+  "file:{{ gramine.runtimedir(libc) }}/",
+  "file:{{ binary_dir }}/{{ entrypoint }}",
+]

libos/test/regression/test_libos.py

@@ -1064,6 +1064,26 @@ def test_150_itimer(self):
         stdout, _ = self.run_binary(['itimer'])
         self.assertIn("TEST OK", stdout)
 
+    def test_160_rlimit_nofile(self):
+        # uses manifest.template
+        stdout, _ = self.run_binary(['rlimit_nofile'])
+        self.assertIn("old RLIMIT_NOFILE soft limit: 900", stdout)
+        self.assertIn("(before setrlimit) opened fd: 899", stdout)
+        self.assertIn("new RLIMIT_NOFILE soft limit: 901", stdout)
+        self.assertIn("(in child, after setrlimit) opened fd: 900", stdout)
+        self.assertIn("(after setrlimit) opened fd: 900", stdout)
+        self.assertIn("TEST OK", stdout)
+
+    def test_161_rlimit_nofile_4k(self):
+        # uses rlimit_nofile_4k.manifest.template
+        stdout, _ = self.run_binary(['rlimit_nofile_4k'])
+        self.assertIn("old RLIMIT_NOFILE soft limit: 4096", stdout)
+        self.assertIn("(before setrlimit) opened fd: 4095", stdout)
+        self.assertIn("new RLIMIT_NOFILE soft limit: 4097", stdout)
+        self.assertIn("(in child, after setrlimit) opened fd: 4096", stdout)
+        self.assertIn("(after setrlimit) opened fd: 4096", stdout)
+        self.assertIn("TEST OK", stdout)
+
 class TC_31_Syscall(RegressionTestCase):
     def test_000_syscall_redirect(self):
         stdout, _ = self.run_binary(['syscall'])

libos/test/regression/tests.toml

@@ -101,6 +101,8 @@ manifests = [
   "readdir",
   "rename_unlink",
   "rename_unlink_fchown",
+  "rlimit_nofile",
+  "rlimit_nofile_4k",
   "run_test",
   "rwlock",
   "sched",

libos/test/regression/tests_musl.toml

@@ -103,6 +103,8 @@ manifests = [
   "readdir",
   "rename_unlink",
   "rename_unlink_fchown",
+  "rlimit_nofile",
+  "rlimit_nofile_4k",
   "run_test",
   "rwlock",
   "sched",

python/graminelibos/manifest_check.py

@@ -130,5 +130,7 @@
         'debug__mock_syscalls': [{Required('name'): str, 'return': int}],
 
         'stack': {'size': _size},
+
+        'fds': {'limit': int},
     },
 })