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, 172 insertions, 0 deletions

diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
new file mode 100644
index 000000000..01b5167fe
--- /dev/null
+++ b/security/selinux/include/avc.h
@@ -0,0 +1,172 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Access vector cache interface for object managers.
+ *
+ * Author : Stephen Smalley, <stephen.smalley.work@gmail.com>
+ */
+
+#ifndef _SELINUX_AVC_H_
+#define _SELINUX_AVC_H_
+
+#include <linux/stddef.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/kdev_t.h>
+#include <linux/spinlock.h>
+#include <linux/init.h>
+#include <linux/audit.h>
+#include <linux/lsm_audit.h>
+#include <linux/in6.h>
+#include "flask.h"
+#include "av_permissions.h"
+#include "security.h"
+
+/*
+ * An entry in the AVC.
+ */
+struct avc_entry;
+
+struct task_struct;
+struct inode;
+struct sock;
+struct sk_buff;
+
+/*
+ * AVC statistics
+ */
+struct avc_cache_stats {
+	unsigned int lookups;
+	unsigned int misses;
+	unsigned int allocations;
+	unsigned int reclaims;
+	unsigned int frees;
+};
+
+/*
+ * We only need this data after we have decided to send an audit message.
+ */
+struct selinux_audit_data {
+	u32 ssid;
+	u32 tsid;
+	u16 tclass;
+	u32 requested;
+	u32 audited;
+	u32 denied;
+	int result;
+} __randomize_layout;
+
+/*
+ * AVC operations
+ */
+
+void __init avc_init(void);
+
+static inline u32 avc_audit_required(u32 requested, struct av_decision *avd,
+				     int result, u32 auditdeny, u32 *deniedp)
+{
+	u32 denied, audited;
+
+	if (avd->flags & AVD_FLAGS_NEVERAUDIT)
+		return 0;
+
+	denied = requested & ~avd->allowed;
+	if (unlikely(denied)) {
+		audited = denied & avd->auditdeny;
+		/*
+		 * auditdeny is TRICKY!  Setting a bit in
+		 * this field means that ANY denials should NOT be audited if
+		 * the policy contains an explicit dontaudit rule for that
+		 * permission.  Take notice that this is unrelated to the
+		 * actual permissions that were denied.  As an example lets
+		 * assume:
+		 *
+		 * denied == READ
+		 * avd.auditdeny & ACCESS == 0 (not set means explicit rule)
+		 * auditdeny & ACCESS == 1
+		 *
+		 * We will NOT audit the denial even though the denied
+		 * permission was READ and the auditdeny checks were for
+		 * ACCESS
+		 */
+		if (auditdeny && !(auditdeny & avd->auditdeny))
+			audited = 0;
+	} else if (result)
+		audited = denied = requested;
+	else
+		audited = requested & avd->auditallow;
+	*deniedp = denied;
+	return audited;
+}
+
+int slow_avc_audit(u32 ssid, u32 tsid, u16 tclass, u32 requested, u32 audited,
+		   u32 denied, int result, struct common_audit_data *a);
+
+/**
+ * avc_audit - Audit the granting or denial of permissions.
+ * @ssid: source security identifier
+ * @tsid: target security identifier
+ * @tclass: target security class
+ * @requested: requested permissions
+ * @avd: access vector decisions
+ * @result: result from avc_has_perm_noaudit
+ * @a:  auxiliary audit data
+ *
+ * Audit the granting or denial of permissions in accordance
+ * with the policy.  This function is typically called by
+ * avc_has_perm() after a permission check, but can also be
+ * called directly by callers who use avc_has_perm_noaudit()
+ * in order to separate the permission check from the auditing.
+ * For example, this separation is useful when the permission check must
+ * be performed under a lock, to allow the lock to be released
+ * before calling the auditing code.
+ */
+static inline int avc_audit(u32 ssid, u32 tsid, u16 tclass, u32 requested,
+			    struct av_decision *avd, int result,
+			    struct common_audit_data *a)
+{
+	u32 audited, denied;
+	audited = avc_audit_required(requested, avd, result, 0, &denied);
+	if (likely(!audited))
+		return 0;
+	return slow_avc_audit(ssid, tsid, tclass, requested, audited, denied,
+			      result, a);
+}
+
+#define AVC_STRICT	   1 /* Ignore permissive mode. */
+#define AVC_EXTENDED_PERMS 2 /* update extended permissions */
+int avc_has_perm_noaudit(u32 ssid, u32 tsid, u16 tclass, u32 requested,
+			 unsigned int flags, struct av_decision *avd);
+
+int avc_has_perm(u32 ssid, u32 tsid, u16 tclass, u32 requested,
+		 struct common_audit_data *auditdata);
+
+#define AVC_EXT_IOCTL	(1 << 0) /* Cache entry for an ioctl extended permission */
+#define AVC_EXT_NLMSG	(1 << 1) /* Cache entry for an nlmsg extended permission */
+int avc_has_extended_perms(u32 ssid, u32 tsid, u16 tclass, u32 requested,
+			   u8 driver, u8 base_perm, u8 perm,
+			   struct common_audit_data *ad);
+
+u32 avc_policy_seqno(void);
+
+#define AVC_CALLBACK_GRANT		1
+#define AVC_CALLBACK_TRY_REVOKE		2
+#define AVC_CALLBACK_REVOKE		4
+#define AVC_CALLBACK_RESET		8
+#define AVC_CALLBACK_AUDITALLOW_ENABLE	16
+#define AVC_CALLBACK_AUDITALLOW_DISABLE 32
+#define AVC_CALLBACK_AUDITDENY_ENABLE	64
+#define AVC_CALLBACK_AUDITDENY_DISABLE	128
+#define AVC_CALLBACK_ADD_XPERMS		256
+
+int avc_add_callback(int (*callback)(u32 event), u32 events);
+
+/* Exported to selinuxfs */
+int avc_get_hash_stats(char *page);
+unsigned int avc_get_cache_threshold(void);
+void avc_set_cache_threshold(unsigned int cache_threshold);
+
+#ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
+DECLARE_PER_CPU(struct avc_cache_stats, avc_cache_stats);
+#endif
+
+#endif /* _SELINUX_AVC_H_ */