24 files changed, 229 insertions, 60 deletions

diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
index 6e000113e508..1abdcd508a11 100644
--- a/arch/arm64/include/asm/brk-imm.h
+++ b/arch/arm64/include/asm/brk-imm.h
@@ -17,6 +17,7 @@
  * 0x401: for compile time BRK instruction
  * 0x800: kernel-mode BUG() and WARN() traps
  * 0x9xx: tag-based KASAN trap (allowed values 0x900 - 0x9ff)
+ * 0x55xx: Undefined Behavior Sanitizer traps ('U' << 8)
  * 0x8xxx: Control-Flow Integrity traps
  */
 #define KPROBES_BRK_IMM			0x004
@@ -28,6 +29,8 @@
 #define BUG_BRK_IMM			0x800
 #define KASAN_BRK_IMM			0x900
 #define KASAN_BRK_MASK			0x0ff
+#define UBSAN_BRK_IMM			0x5500
+#define UBSAN_BRK_MASK			0x00ff
 
 #define CFI_BRK_IMM_TARGET		GENMASK(4, 0)
 #define CFI_BRK_IMM_TYPE		GENMASK(9, 5)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 4c0caa589e12..87f42eb1c950 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -26,6 +26,7 @@
 #include <linux/syscalls.h>
 #include <linux/mm_types.h>
 #include <linux/kasan.h>
+#include <linux/ubsan.h>
 #include <linux/cfi.h>
 
 #include <asm/atomic.h>
@@ -1074,6 +1075,19 @@ static struct break_hook kasan_break_hook = {
 };
 #endif
 
+#ifdef CONFIG_UBSAN_TRAP
+static int ubsan_handler(struct pt_regs *regs, unsigned long esr)
+{
+	die(report_ubsan_failure(regs, esr & UBSAN_BRK_MASK), regs, esr);
+	return DBG_HOOK_HANDLED;
+}
+
+static struct break_hook ubsan_break_hook = {
+	.fn	= ubsan_handler,
+	.imm	= UBSAN_BRK_IMM,
+	.mask	= UBSAN_BRK_MASK,
+};
+#endif
 
 #define esr_comment(esr) ((esr) & ESR_ELx_BRK64_ISS_COMMENT_MASK)
 
@@ -1092,6 +1106,10 @@ int __init early_brk64(unsigned long addr, unsigned long esr,
 	if ((esr_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
 		return kasan_handler(regs, esr) != DBG_HOOK_HANDLED;
 #endif
+#ifdef CONFIG_UBSAN_TRAP
+	if ((esr_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM)
+		return ubsan_handler(regs, esr) != DBG_HOOK_HANDLED;
+#endif
 	return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
 }
 
@@ -1105,5 +1123,8 @@ void __init trap_init(void)
 #ifdef CONFIG_KASAN_SW_TAGS
 	register_kernel_break_hook(&kasan_break_hook);
 #endif
+#ifdef CONFIG_UBSAN_TRAP
+	register_kernel_break_hook(&ubsan_break_hook);
+#endif
 	debug_traps_init();
 }
diff --git a/drivers/crypto/hisilicon/sgl.c b/drivers/crypto/hisilicon/sgl.c
index 2b6f2281cfd6..0974b0041405 100644
--- a/drivers/crypto/hisilicon/sgl.c
+++ b/drivers/crypto/hisilicon/sgl.c
@@ -124,9 +124,8 @@ err_free_mem:
 	for (j = 0; j < i; j++) {
 		dma_free_coherent(dev, block_size, block[j].sgl,
 				  block[j].sgl_dma);
-		memset(block + j, 0, sizeof(*block));
 	}
-	kfree(pool);
+	kfree_sensitive(pool);
 	return ERR_PTR(-ENOMEM);
 }
 EXPORT_SYMBOL_GPL(hisi_acc_create_sgl_pool);
diff --git a/drivers/gpu/drm/i915/gvt/firmware.c b/drivers/gpu/drm/i915/gvt/firmware.c
index a683c22d5b64..dce93738e98a 100644
--- a/drivers/gpu/drm/i915/gvt/firmware.c
+++ b/drivers/gpu/drm/i915/gvt/firmware.c
@@ -45,7 +45,7 @@ struct gvt_firmware_header {
 	u64 cfg_space_offset;	/* offset in the file */
 	u64 mmio_size;
 	u64 mmio_offset;	/* offset in the file */
-	unsigned char data[1];
+	unsigned char data[];
 };
 
 #define dev_to_drm_minor(d) dev_get_drvdata((d))
@@ -77,7 +77,7 @@ static int expose_firmware_sysfs(struct intel_gvt *gvt)
 	unsigned long size, crc32_start;
 	int ret;
 
-	size = sizeof(*h) + info->mmio_size + info->cfg_space_size;
+	size = offsetof(struct gvt_firmware_header, data) + info->mmio_size + info->cfg_space_size;
 	firmware = vzalloc(size);
 	if (!firmware)
 		return -ENOMEM;
diff --git a/drivers/gpu/drm/nouveau/include/nvif/outp.h b/drivers/gpu/drm/nouveau/include/nvif/outp.h
index 45daadec3c0c..fa76a7b5e4b3 100644
--- a/drivers/gpu/drm/nouveau/include/nvif/outp.h
+++ b/drivers/gpu/drm/nouveau/include/nvif/outp.h
@@ -3,6 +3,7 @@
 #define __NVIF_OUTP_H__
 #include <nvif/object.h>
 #include <nvif/if0012.h>
+#include <drm/display/drm_dp.h>
 struct nvif_disp;
 
 struct nvif_outp {
@@ -21,7 +22,7 @@ int nvif_outp_acquire_rgb_crt(struct nvif_outp *);
 int nvif_outp_acquire_tmds(struct nvif_outp *, int head,
 			   bool hdmi, u8 max_ac_packet, u8 rekey, u8 scdc, bool hda);
 int nvif_outp_acquire_lvds(struct nvif_outp *, bool dual, bool bpc8);
-int nvif_outp_acquire_dp(struct nvif_outp *, u8 dpcd[16],
+int nvif_outp_acquire_dp(struct nvif_outp *outp, u8 dpcd[DP_RECEIVER_CAP_SIZE],
 			 int link_nr, int link_bw, bool hda, bool mst);
 void nvif_outp_release(struct nvif_outp *);
 int nvif_outp_infoframe(struct nvif_outp *, u8 type, struct nvif_outp_infoframe_v0 *, u32 size);
diff --git a/drivers/gpu/drm/nouveau/nvif/outp.c b/drivers/gpu/drm/nouveau/nvif/outp.c
index 7da39f1eae9f..c24bc5eae3ec 100644
--- a/drivers/gpu/drm/nouveau/nvif/outp.c
+++ b/drivers/gpu/drm/nouveau/nvif/outp.c
@@ -127,7 +127,7 @@ nvif_outp_acquire(struct nvif_outp *outp, u8 proto, struct nvif_outp_acquire_v0
 }
 
 int
-nvif_outp_acquire_dp(struct nvif_outp *outp, u8 dpcd[16],
+nvif_outp_acquire_dp(struct nvif_outp *outp, u8 dpcd[DP_RECEIVER_CAP_SIZE],
 		     int link_nr, int link_bw, bool hda, bool mst)
 {
 	struct nvif_outp_acquire_v0 args;
diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c
index 62516078a619..0ce4cbf6abda 100644
--- a/drivers/misc/lkdtm/heap.c
+++ b/drivers/misc/lkdtm/heap.c
@@ -31,6 +31,7 @@ static void lkdtm_VMALLOC_LINEAR_OVERFLOW(void)
 	char *one, *two;
 
 	one = vzalloc(PAGE_SIZE);
+	OPTIMIZER_HIDE_VAR(one);
 	two = vzalloc(PAGE_SIZE);
 
 	pr_info("Attempting vmalloc linear overflow ...\n");
diff --git a/drivers/net/ethernet/intel/i40e/i40e.h b/drivers/net/ethernet/intel/i40e/i40e.h
index 60e351665c70..3a1c28ca5bb4 100644
--- a/drivers/net/ethernet/intel/i40e/i40e.h
+++ b/drivers/net/ethernet/intel/i40e/i40e.h
@@ -176,7 +176,7 @@ enum i40e_interrupt_policy {
 
 struct i40e_lump_tracking {
 	u16 num_entries;
-	u16 list[0];
+	u16 list[];
 #define I40E_PILE_VALID_BIT  0x8000
 #define I40E_IWARP_IRQ_PILE_ID  (I40E_PILE_VALID_BIT - 2)
 };
diff --git a/drivers/soc/ixp4xx/ixp4xx-npe.c b/drivers/soc/ixp4xx/ixp4xx-npe.c
index 58240e320c13..5be9988f30ce 100644
--- a/drivers/soc/ixp4xx/ixp4xx-npe.c
+++ b/drivers/soc/ixp4xx/ixp4xx-npe.c
@@ -519,15 +519,15 @@ int npe_load_firmware(struct npe *npe, const char *name, struct device *dev)
 		u32 id;
 		u32 size;
 		union {
-			u32 data[0];
-			struct dl_block blocks[0];
+			DECLARE_FLEX_ARRAY(u32, data);
+			DECLARE_FLEX_ARRAY(struct dl_block, blocks);
 		};
 	} *image;
 
 	struct dl_codeblock {
 		u32 npe_addr;
 		u32 size;
-		u32 data[0];
+		u32 data[];
 	} *cb;
 
 	int i, j, err, data_size, instr_size, blocks, table_end;
diff --git a/fs/coda/upcall.c b/fs/coda/upcall.c
index 59f6cfd06f96..cd6a3721f6f6 100644
--- a/fs/coda/upcall.c
+++ b/fs/coda/upcall.c
@@ -791,7 +791,7 @@ static int coda_upcall(struct venus_comm *vcp,
 	sig_req = kmalloc(sizeof(struct upc_req), GFP_KERNEL);
 	if (!sig_req) goto exit;
 
-	sig_inputArgs = kvzalloc(sizeof(struct coda_in_hdr), GFP_KERNEL);
+	sig_inputArgs = kvzalloc(sizeof(*sig_inputArgs), GFP_KERNEL);
 	if (!sig_inputArgs) {
 		kfree(sig_req);
 		goto exit;
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index d233c24ea342..e2b8b3437c58 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -491,6 +491,11 @@ static void ext4_sb_release(struct kobject *kobj)
 	complete(&sbi->s_kobj_unregister);
 }
 
+static void ext4_feat_release(struct kobject *kobj)
+{
+	kfree(kobj);
+}
+
 static const struct sysfs_ops ext4_attr_ops = {
 	.show	= ext4_attr_show,
 	.store	= ext4_attr_store,
@@ -505,7 +510,7 @@ static struct kobj_type ext4_sb_ktype = {
 static struct kobj_type ext4_feat_ktype = {
 	.default_groups = ext4_feat_groups,
 	.sysfs_ops	= &ext4_attr_ops,
-	.release	= (void (*)(struct kobject *))kfree,
+	.release	= ext4_feat_release,
 };
 
 void ext4_notify_error_sysfs(struct ext4_sb_info *sbi)
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 898b3458b24a..56467f86a27c 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -297,6 +297,11 @@
  *
  * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size
  */
+#if __has_attribute(__pass_dynamic_object_size__)
+# define __pass_dynamic_object_size(type)	__attribute__((__pass_dynamic_object_size__(type)))
+#else
+# define __pass_dynamic_object_size(type)
+#endif
 #if __has_attribute(__pass_object_size__)
 # define __pass_object_size(type)	__attribute__((__pass_object_size__(type)))
 #else
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 7cad8bb031e9..c9de1f59ee80 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -90,10 +90,17 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size)
  * size, rather than struct size), but there remain some stragglers using
  * type 0 that will be converted in the future.
  */
+#if __has_builtin(__builtin_dynamic_object_size)
+#define POS			__pass_dynamic_object_size(1)
+#define POS0			__pass_dynamic_object_size(0)
+#define __struct_size(p)	__builtin_dynamic_object_size(p, 0)
+#define __member_size(p)	__builtin_dynamic_object_size(p, 1)
+#else
 #define POS			__pass_object_size(1)
 #define POS0			__pass_object_size(0)
 #define __struct_size(p)	__builtin_object_size(p, 0)
 #define __member_size(p)	__builtin_object_size(p, 1)
+#endif
 
 #define __compiletime_lessthan(bounds, length)	(	\
 	__builtin_constant_p((bounds) < (length)) &&	\
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index afb18f198843..ab9728138ad6 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -329,6 +329,10 @@ copy_struct_from_user(void *dst, size_t ksize, const void __user *src,
 	size_t size = min(ksize, usize);
 	size_t rest = max(ksize, usize) - size;
 
+	/* Double check if ksize is larger than a known object size. */
+	if (WARN_ON_ONCE(ksize > __builtin_object_size(dst, 1)))
+		return -E2BIG;
+
 	/* Deal with trailing bytes. */
 	if (usize < ksize) {
 		memset(dst + size, 0, rest);
diff --git a/include/linux/ubsan.h b/include/linux/ubsan.h
new file mode 100644
index 000000000000..bff7445498de
--- /dev/null
+++ b/include/linux/ubsan.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_UBSAN_H
+#define _LINUX_UBSAN_H
+
+#ifdef CONFIG_UBSAN_TRAP
+const char *report_ubsan_failure(struct pt_regs *regs, u32 check_type);
+#endif
+
+#endif
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 97661a60b28c..709de6d4feb2 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -631,7 +631,7 @@ struct io_uring_buf_ring {
 			__u16	resv3;
 			__u16	tail;
 		};
-		struct io_uring_buf	bufs[0];
+		__DECLARE_FLEX_ARRAY(struct io_uring_buf, bufs);
 	};
 };
 
diff --git a/lib/Makefile b/lib/Makefile
index a4665a802e87..36938c564a2a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -340,9 +340,7 @@ quiet_cmd_build_OID_registry = GEN     $@
 clean-files	+= oid_registry_data.c
 
 obj-$(CONFIG_UCS2_STRING) += ucs2_string.o
-ifneq ($(CONFIG_UBSAN_TRAP),y)
 obj-$(CONFIG_UBSAN) += ubsan.o
-endif
 
 UBSAN_SANITIZE_ubsan.o := n
 KASAN_SANITIZE_ubsan.o := n
diff --git a/lib/string.c b/lib/string.c
index 4fb566ea610f..3d55ef890106 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -480,13 +480,11 @@ EXPORT_SYMBOL(strcspn);
  */
 char *strpbrk(const char *cs, const char *ct)
 {
-	const char *sc1, *sc2;
+	const char *sc;
 
-	for (sc1 = cs; *sc1 != '\0'; ++sc1) {
-		for (sc2 = ct; *sc2 != '\0'; ++sc2) {
-			if (*sc1 == *sc2)
-				return (char *)sc1;
-		}
+	for (sc = cs; *sc != '\0'; ++sc) {
+		if (strchr(ct, *sc))
+			return (char *)sc;
 	}
 	return NULL;
 }
diff --git a/lib/ubsan.c b/lib/ubsan.c
index 4d39e0babb98..e2cc4a799312 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -14,10 +14,76 @@
 #include <linux/types.h>
 #include <linux/sched.h>
 #include <linux/uaccess.h>
+#include <linux/ubsan.h>
 #include <kunit/test-bug.h>
 
 #include "ubsan.h"
 
+#ifdef CONFIG_UBSAN_TRAP
+/*
+ * Only include matches for UBSAN checks that are actually compiled in.
+ * The mappings of struct SanitizerKind (the -fsanitize=xxx args) to
+ * enum SanitizerHandler (the traps) in Clang is in clang/lib/CodeGen/.
+ */
+const char *report_ubsan_failure(struct pt_regs *regs, u32 check_type)
+{
+	switch (check_type) {
+#ifdef CONFIG_UBSAN_BOUNDS
+	/*
+	 * SanitizerKind::ArrayBounds and SanitizerKind::LocalBounds
+	 * emit SanitizerHandler::OutOfBounds.
+	 */
+	case ubsan_out_of_bounds:
+		return "UBSAN: array index out of bounds";
+#endif
+#ifdef CONFIG_UBSAN_SHIFT
+	/*
+	 * SanitizerKind::ShiftBase and SanitizerKind::ShiftExponent
+	 * emit SanitizerHandler::ShiftOutOfBounds.
+	 */
+	case ubsan_shift_out_of_bounds:
+		return "UBSAN: shift out of bounds";
+#endif
+#ifdef CONFIG_UBSAN_DIV_ZERO
+	/*
+	 * SanitizerKind::IntegerDivideByZero emits
+	 * SanitizerHandler::DivremOverflow.
+	 */
+	case ubsan_divrem_overflow:
+		return "UBSAN: divide/remainder overflow";
+#endif
+#ifdef CONFIG_UBSAN_UNREACHABLE
+	/*
+	 * SanitizerKind::Unreachable emits
+	 * SanitizerHandler::BuiltinUnreachable.
+	 */
+	case ubsan_builtin_unreachable:
+		return "UBSAN: unreachable code";
+#endif
+#if defined(CONFIG_UBSAN_BOOL) || defined(CONFIG_UBSAN_ENUM)
+	/*
+	 * SanitizerKind::Bool and SanitizerKind::Enum emit
+	 * SanitizerHandler::LoadInvalidValue.
+	 */
+	case ubsan_load_invalid_value:
+		return "UBSAN: loading invalid value";
+#endif
+#ifdef CONFIG_UBSAN_ALIGNMENT
+	/*
+	 * SanitizerKind::Alignment emits SanitizerHandler::TypeMismatch
+	 * or SanitizerHandler::AlignmentAssumption.
+	 */
+	case ubsan_alignment_assumption:
+		return "UBSAN: alignment assumption";
+	case ubsan_type_mismatch:
+		return "UBSAN: type mismatch";
+#endif
+	default:
+		return "UBSAN: unrecognized failure code";
+	}
+}
+
+#else
 static const char * const type_check_kinds[] = {
 	"load of",
 	"store to",
@@ -387,3 +453,5 @@ void __ubsan_handle_alignment_assumption(void *_data, unsigned long ptr,
 	ubsan_epilogue();
 }
 EXPORT_SYMBOL(__ubsan_handle_alignment_assumption);
+
+#endif /* !CONFIG_UBSAN_TRAP */
diff --git a/lib/ubsan.h b/lib/ubsan.h
index 9a0b71c5ff9f..cc5cb94895a6 100644
--- a/lib/ubsan.h
+++ b/lib/ubsan.h
@@ -2,6 +2,38 @@
 #ifndef _LIB_UBSAN_H
 #define _LIB_UBSAN_H
 
+/*
+ * ABI defined by Clang's UBSAN enum SanitizerHandler:
+ * https://github.com/llvm/llvm-project/blob/release/16.x/clang/lib/CodeGen/CodeGenFunction.h#L113
+ */
+enum ubsan_checks {
+	ubsan_add_overflow,
+	ubsan_builtin_unreachable,
+	ubsan_cfi_check_fail,
+	ubsan_divrem_overflow,
+	ubsan_dynamic_type_cache_miss,
+	ubsan_float_cast_overflow,
+	ubsan_function_type_mismatch,
+	ubsan_implicit_conversion,
+	ubsan_invalid_builtin,
+	ubsan_invalid_objc_cast,
+	ubsan_load_invalid_value,
+	ubsan_missing_return,
+	ubsan_mul_overflow,
+	ubsan_negate_overflow,
+	ubsan_nullability_arg,
+	ubsan_nullability_return,
+	ubsan_nonnull_arg,
+	ubsan_nonnull_return,
+	ubsan_out_of_bounds,
+	ubsan_pointer_overflow,
+	ubsan_shift_out_of_bounds,
+	ubsan_sub_overflow,
+	ubsan_type_mismatch,
+	ubsan_alignment_assumption,
+	ubsan_vla_bound_not_positive,
+};
+
 enum {
 	type_kind_int = 0,
 	type_kind_float = 1,
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 433060cade03..3931a4bba8af 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -795,7 +795,7 @@ struct rxrpc_txbuf {
 			u8	data[RXRPC_JUMBO_DATALEN]; /* Data packet */
 			struct {
 				struct rxrpc_ackpacket ack;
-				u8 acks[0];
+				DECLARE_FLEX_ARRAY(u8, acks);
 			};
 		};
 	} __aligned(64);
diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index b34d11e22636..320afd3cf8e8 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -29,7 +29,7 @@ GCC_PLUGINS_DIR = $(shell $(CC) -print-file-name=plugin)
 plugin_cxxflags	= -Wp,-MMD,$(depfile) $(KBUILD_HOSTCXXFLAGS) -fPIC \
 		  -include $(srctree)/include/linux/compiler-version.h \
 		  -DPLUGIN_VERSION=$(call stringify,$(KERNELVERSION)) \
-		  -I $(GCC_PLUGINS_DIR)/include -I $(obj) -std=gnu++11 \
+		  -I $(GCC_PLUGINS_DIR)/include -I $(obj) \
 		  -fno-rtti -fno-exceptions -fasynchronous-unwind-tables \
 		  -ggdb -Wno-narrowing -Wno-unused-variable \
 		  -Wno-format-diag
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index 53baa95cb644..0f295961e773 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -281,6 +281,9 @@ endmenu
 
 config CC_HAS_RANDSTRUCT
 	def_bool $(cc-option,-frandomize-layout-seed-file=/dev/null)
+	# Randstruct was first added in Clang 15, but it isn't safe to use until
+	# Clang 16 due to https://github.com/llvm/llvm-project/issues/60349
+	depends on !CC_IS_CLANG || CLANG_VERSION >= 160000
 
 choice
 	prompt "Randomize layout of sensitive kernel structures"
diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index 110a5ab2b46b..d73a281adf86 100644
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -52,7 +52,6 @@ static bool deny_reading_verity_digests;
 #endif
 
 #ifdef CONFIG_SYSCTL
-
 static struct ctl_path loadpin_sysctl_path[] = {
 	{ .procname = "kernel", },
 	{ .procname = "loadpin", },
@@ -66,59 +65,70 @@ static struct ctl_table loadpin_sysctl_table[] = {
 		.maxlen         = sizeof(int),
 		.mode           = 0644,
 		.proc_handler   = proc_dointvec_minmax,
-		.extra1         = SYSCTL_ZERO,
+		.extra1         = SYSCTL_ONE,
 		.extra2         = SYSCTL_ONE,
 	},
 	{ }
 };
 
-/*
- * This must be called after early kernel init, since then the rootdev
- * is available.
- */
-static void check_pinning_enforcement(struct super_block *mnt_sb)
+static void set_sysctl(bool is_writable)
 {
-	bool ro = false;
-
 	/*
 	 * If load pinning is not enforced via a read-only block
 	 * device, allow sysctl to change modes for testing.
 	 */
+	if (is_writable)
+		loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO;
+	else
+		loadpin_sysctl_table[0].extra1 = SYSCTL_ONE;
+}
+#else
+static inline void set_sysctl(bool is_writable) { }
+#endif
+
+static void report_writable(struct super_block *mnt_sb, bool writable)
+{
 	if (mnt_sb->s_bdev) {
-		ro = bdev_read_only(mnt_sb->s_bdev);
 		pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
 			MAJOR(mnt_sb->s_bdev->bd_dev),
 			MINOR(mnt_sb->s_bdev->bd_dev),
-			ro ? "read-only" : "writable");
+			writable ? "writable" : "read-only");
 	} else
 		pr_info("mnt_sb lacks block device, treating as: writable\n");
 
-	if (!ro) {
-		if (!register_sysctl_paths(loadpin_sysctl_path,
-					   loadpin_sysctl_table))
-			pr_notice("sysctl registration failed!\n");
-		else
-			pr_info("enforcement can be disabled.\n");
-	} else
+	if (!writable)
 		pr_info("load pinning engaged.\n");
 }
-#else
-static void check_pinning_enforcement(struct super_block *mnt_sb)
+
+/*
+ * This must be called after early kernel init, since then the rootdev
+ * is available.
+ */
+static bool sb_is_writable(struct super_block *mnt_sb)
 {
-	pr_info("load pinning engaged.\n");
+	bool writable = true;
+
+	if (mnt_sb->s_bdev)
+		writable = !bdev_read_only(mnt_sb->s_bdev);
+
+	return writable;
 }
-#endif
 
 static void loadpin_sb_free_security(struct super_block *mnt_sb)
 {
 	/*
 	 * When unmounting the filesystem we were using for load
 	 * pinning, we acknowledge the superblock release, but make sure
-	 * no other modules or firmware can be loaded.
+	 * no other modules or firmware can be loaded when we are in
+	 * enforcing mode. Otherwise, allow the root to be reestablished.
 	 */
 	if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
-		pinned_root = ERR_PTR(-EIO);
-		pr_info("umount pinned fs: refusing further loads\n");
+		if (enforce) {
+			pinned_root = ERR_PTR(-EIO);
+			pr_info("umount pinned fs: refusing further loads\n");
+		} else {
+			pinned_root = NULL;
+		}
 	}
 }
 
@@ -126,6 +136,8 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
 {
 	struct super_block *load_root;
 	const char *origin = kernel_read_file_id_str(id);
+	bool first_root_pin = false;
+	bool load_root_writable;
 
 	/* If the file id is excluded, ignore the pinning. */
 	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
@@ -146,26 +158,25 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
 	}
 
 	load_root = file->f_path.mnt->mnt_sb;
+	load_root_writable = sb_is_writable(load_root);
 
 	/* First loaded module/firmware defines the root for all others. */
 	spin_lock(&pinned_root_spinlock);
 	/*
-	 * pinned_root is only NULL at startup. Otherwise, it is either
-	 * a valid reference, or an ERR_PTR.
+	 * pinned_root is only NULL at startup or when the pinned root has
+	 * been unmounted while we are not in enforcing mode. Otherwise, it
+	 * is either a valid reference, or an ERR_PTR.
 	 */
 	if (!pinned_root) {
 		pinned_root = load_root;
-		/*
-		 * Unlock now since it's only pinned_root we care about.
-		 * In the worst case, we will (correctly) report pinning
-		 * failures before we have announced that pinning is
-		 * enforcing. This would be purely cosmetic.
-		 */
-		spin_unlock(&pinned_root_spinlock);
-		check_pinning_enforcement(pinned_root);
+		first_root_pin = true;
+	}
+	spin_unlock(&pinned_root_spinlock);
+
+	if (first_root_pin) {
+		report_writable(pinned_root, load_root_writable);
+		set_sysctl(load_root_writable);
 		report_load(origin, file, "pinned");
-	} else {
-		spin_unlock(&pinned_root_spinlock);
 	}
 
 	if (IS_ERR_OR_NULL(pinned_root) ||
@@ -250,6 +261,10 @@ static int __init loadpin_init(void)
 	pr_info("ready to pin (currently %senforcing)\n",
 		enforce ? "" : "not ");
 	parse_exclude();
+#ifdef CONFIG_SYSCTL
+	if (!register_sysctl_paths(loadpin_sysctl_path, loadpin_sysctl_table))
+		pr_notice("sysctl registration failed!\n");
+#endif
 	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
 
 	return 0;