kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 323 insertions, 0 deletions

diff --git a/security/keys/proc.c b/security/keys/proc.c
new file mode 100644
index 000000000..4f4e2c182
--- /dev/null
+++ b/security/keys/proc.c
@@ -0,0 +1,323 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* procfs files for key database enumeration
+ *
+ * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <asm/errno.h>
+#include "internal.h"
+
+static void *proc_keys_start(struct seq_file *p, loff_t *_pos);
+static void *proc_keys_next(struct seq_file *p, void *v, loff_t *_pos);
+static void proc_keys_stop(struct seq_file *p, void *v);
+static int proc_keys_show(struct seq_file *m, void *v);
+
+static const struct seq_operations proc_keys_ops = {
+	.start	= proc_keys_start,
+	.next	= proc_keys_next,
+	.stop	= proc_keys_stop,
+	.show	= proc_keys_show,
+};
+
+static void *proc_key_users_start(struct seq_file *p, loff_t *_pos);
+static void *proc_key_users_next(struct seq_file *p, void *v, loff_t *_pos);
+static void proc_key_users_stop(struct seq_file *p, void *v);
+static int proc_key_users_show(struct seq_file *m, void *v);
+
+static const struct seq_operations proc_key_users_ops = {
+	.start	= proc_key_users_start,
+	.next	= proc_key_users_next,
+	.stop	= proc_key_users_stop,
+	.show	= proc_key_users_show,
+};
+
+/*
+ * Declare the /proc files.
+ */
+static int __init key_proc_init(void)
+{
+	struct proc_dir_entry *p;
+
+	p = proc_create_seq("keys", 0, NULL, &proc_keys_ops);
+	if (!p)
+		panic("Cannot create /proc/keys\n");
+
+	p = proc_create_seq("key-users", 0, NULL, &proc_key_users_ops);
+	if (!p)
+		panic("Cannot create /proc/key-users\n");
+
+	return 0;
+}
+
+__initcall(key_proc_init);
+
+/*
+ * Implement "/proc/keys" to provide a list of the keys on the system that
+ * grant View permission to the caller.
+ */
+static struct rb_node *key_serial_next(struct seq_file *p, struct rb_node *n)
+{
+	struct user_namespace *user_ns = seq_user_ns(p);
+
+	n = rb_next(n);
+	while (n) {
+		struct key *key = rb_entry(n, struct key, serial_node);
+		if (kuid_has_mapping(user_ns, key->user->uid))
+			break;
+		n = rb_next(n);
+	}
+	return n;
+}
+
+static struct key *find_ge_key(struct seq_file *p, key_serial_t id)
+{
+	struct user_namespace *user_ns = seq_user_ns(p);
+	struct rb_node *n = key_serial_tree.rb_node;
+	struct key *minkey = NULL;
+
+	while (n) {
+		struct key *key = rb_entry(n, struct key, serial_node);
+		if (id < key->serial) {
+			if (!minkey || minkey->serial > key->serial)
+				minkey = key;
+			n = n->rb_left;
+		} else if (id > key->serial) {
+			n = n->rb_right;
+		} else {
+			minkey = key;
+			break;
+		}
+		key = NULL;
+	}
+
+	if (!minkey)
+		return NULL;
+
+	for (;;) {
+		if (kuid_has_mapping(user_ns, minkey->user->uid))
+			return minkey;
+		n = rb_next(&minkey->serial_node);
+		if (!n)
+			return NULL;
+		minkey = rb_entry(n, struct key, serial_node);
+	}
+}
+
+static void *proc_keys_start(struct seq_file *p, loff_t *_pos)
+	__acquires(key_serial_lock)
+{
+	key_serial_t pos = *_pos;
+	struct key *key;
+
+	spin_lock(&key_serial_lock);
+
+	if (*_pos > INT_MAX)
+		return NULL;
+	key = find_ge_key(p, pos);
+	if (!key)
+		return NULL;
+	*_pos = key->serial;
+	return &key->serial_node;
+}
+
+static inline key_serial_t key_node_serial(struct rb_node *n)
+{
+	struct key *key = rb_entry(n, struct key, serial_node);
+	return key->serial;
+}
+
+static void *proc_keys_next(struct seq_file *p, void *v, loff_t *_pos)
+{
+	struct rb_node *n;
+
+	n = key_serial_next(p, v);
+	if (n)
+		*_pos = key_node_serial(n);
+	else
+		(*_pos)++;
+	return n;
+}
+
+static void proc_keys_stop(struct seq_file *p, void *v)
+	__releases(key_serial_lock)
+{
+	spin_unlock(&key_serial_lock);
+}
+
+static int proc_keys_show(struct seq_file *m, void *v)
+{
+	struct rb_node *_p = v;
+	struct key *key = rb_entry(_p, struct key, serial_node);
+	unsigned long flags;
+	key_ref_t key_ref, skey_ref;
+	time64_t now, expiry;
+	char xbuf[16];
+	short state;
+	u64 timo;
+	int rc;
+
+	struct keyring_search_context ctx = {
+		.index_key		= key->index_key,
+		.cred			= m->file->f_cred,
+		.match_data.cmp		= lookup_user_key_possessed,
+		.match_data.raw_data	= key,
+		.match_data.lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
+		.flags			= (KEYRING_SEARCH_NO_STATE_CHECK |
+					   KEYRING_SEARCH_RECURSE),
+	};
+
+	key_ref = make_key_ref(key, 0);
+
+	/* determine if the key is possessed by this process (a test we can
+	 * skip if the key does not indicate the possessor can view it
+	 */
+	if (key->perm & KEY_POS_VIEW) {
+		rcu_read_lock();
+		skey_ref = search_cred_keyrings_rcu(&ctx);
+		rcu_read_unlock();
+		if (!IS_ERR(skey_ref)) {
+			key_ref_put(skey_ref);
+			key_ref = make_key_ref(key, 1);
+		}
+	}
+
+	/* check whether the current task is allowed to view the key */
+	rc = key_task_permission(key_ref, ctx.cred, KEY_NEED_VIEW);
+	if (rc < 0)
+		return 0;
+
+	now = ktime_get_real_seconds();
+
+	rcu_read_lock();
+
+	/* come up with a suitable timeout value */
+	expiry = READ_ONCE(key->expiry);
+	if (expiry == TIME64_MAX) {
+		memcpy(xbuf, "perm", 5);
+	} else if (now >= expiry) {
+		memcpy(xbuf, "expd", 5);
+	} else {
+		timo = expiry - now;
+
+		if (timo < 60)
+			sprintf(xbuf, "%llus", timo);
+		else if (timo < 60*60)
+			sprintf(xbuf, "%llum", div_u64(timo, 60));
+		else if (timo < 60*60*24)
+			sprintf(xbuf, "%lluh", div_u64(timo, 60 * 60));
+		else if (timo < 60*60*24*7)
+			sprintf(xbuf, "%llud", div_u64(timo, 60 * 60 * 24));
+		else
+			sprintf(xbuf, "%lluw", div_u64(timo, 60 * 60 * 24 * 7));
+	}
+
+	state = key_read_state(key);
+
+#define showflag(FLAGS, LETTER, FLAG) \
+	((FLAGS & (1 << FLAG)) ? LETTER : '-')
+
+	flags = READ_ONCE(key->flags);
+	seq_printf(m, "%08x %c%c%c%c%c%c%c %5d %4s %08x %5d %5d %-9.9s ",
+		   key->serial,
+		   state != KEY_IS_UNINSTANTIATED ? 'I' : '-',
+		   showflag(flags, 'R', KEY_FLAG_REVOKED),
+		   showflag(flags, 'D', KEY_FLAG_DEAD),
+		   showflag(flags, 'Q', KEY_FLAG_IN_QUOTA),
+		   showflag(flags, 'U', KEY_FLAG_USER_CONSTRUCT),
+		   state < 0 ? 'N' : '-',
+		   showflag(flags, 'i', KEY_FLAG_INVALIDATED),
+		   refcount_read(&key->usage),
+		   xbuf,
+		   key->perm,
+		   from_kuid_munged(seq_user_ns(m), key->uid),
+		   from_kgid_munged(seq_user_ns(m), key->gid),
+		   key->type->name);
+
+#undef showflag
+
+	if (key->type->describe)
+		key->type->describe(key, m);
+	seq_putc(m, '\n');
+
+	rcu_read_unlock();
+	return 0;
+}
+
+static struct rb_node *__key_user_next(struct user_namespace *user_ns, struct rb_node *n)
+{
+	while (n) {
+		struct key_user *user = rb_entry(n, struct key_user, node);
+		if (kuid_has_mapping(user_ns, user->uid))
+			break;
+		n = rb_next(n);
+	}
+	return n;
+}
+
+static struct rb_node *key_user_next(struct user_namespace *user_ns, struct rb_node *n)
+{
+	return __key_user_next(user_ns, rb_next(n));
+}
+
+static struct rb_node *key_user_first(struct user_namespace *user_ns, struct rb_root *r)
+{
+	struct rb_node *n = rb_first(r);
+	return __key_user_next(user_ns, n);
+}
+
+static void *proc_key_users_start(struct seq_file *p, loff_t *_pos)
+	__acquires(key_user_lock)
+{
+	struct rb_node *_p;
+	loff_t pos = *_pos;
+
+	spin_lock(&key_user_lock);
+
+	_p = key_user_first(seq_user_ns(p), &key_user_tree);
+	while (pos > 0 && _p) {
+		pos--;
+		_p = key_user_next(seq_user_ns(p), _p);
+	}
+
+	return _p;
+}
+
+static void *proc_key_users_next(struct seq_file *p, void *v, loff_t *_pos)
+{
+	(*_pos)++;
+	return key_user_next(seq_user_ns(p), (struct rb_node *)v);
+}
+
+static void proc_key_users_stop(struct seq_file *p, void *v)
+	__releases(key_user_lock)
+{
+	spin_unlock(&key_user_lock);
+}
+
+static int proc_key_users_show(struct seq_file *m, void *v)
+{
+	struct rb_node *_p = v;
+	struct key_user *user = rb_entry(_p, struct key_user, node);
+	unsigned maxkeys = uid_eq(user->uid, GLOBAL_ROOT_UID) ?
+		key_quota_root_maxkeys : key_quota_maxkeys;
+	unsigned maxbytes = uid_eq(user->uid, GLOBAL_ROOT_UID) ?
+		key_quota_root_maxbytes : key_quota_maxbytes;
+
+	seq_printf(m, "%5u: %5d %d/%d %d/%d %d/%d\n",
+		   from_kuid_munged(seq_user_ns(m), user->uid),
+		   refcount_read(&user->usage),
+		   atomic_read(&user->nkeys),
+		   atomic_read(&user->nikeys),
+		   user->qnkeys,
+		   maxkeys,
+		   user->qnbytes,
+		   maxbytes);
+
+	return 0;
+}