diff --git a/sys/cddl/dev/dtrace/amd64/dtrace_isa.c b/sys/cddl/dev/dtrace/amd64/dtrace_isa.c
index 83d34abbd27..f14e90d974b 100644
--- a/sys/cddl/dev/dtrace/amd64/dtrace_isa.c
+++ b/sys/cddl/dev/dtrace/amd64/dtrace_isa.c
@@ -29,6 +29,7 @@
 #include <sys/systm.h>
 #include <sys/dtrace_impl.h>
 #include <sys/kernel.h>
+#include <sys/msan.h>
 #include <sys/stack.h>
 #include <sys/pcpu.h>
 
@@ -73,6 +74,8 @@ dtrace_getpcstack(pc_t *pcstack, int pcstack_limit, int aframes,
 	frame = (struct amd64_frame *)rbp;
 	td = curthread;
 	while (depth < pcstack_limit) {
+		kmsan_mark(frame, sizeof(*frame), KMSAN_STATE_INITED);
+
 		if (!kstack_contains(curthread, (vm_offset_t)frame,
 		    sizeof(*frame)))
 			break;
@@ -99,6 +102,7 @@ dtrace_getpcstack(pc_t *pcstack, int pcstack_limit, int aframes,
 	for (; depth < pcstack_limit; depth++) {
 		pcstack[depth] = 0;
 	}
+	kmsan_check(pcstack, pcstack_limit * sizeof(*pcstack), "dtrace");
 }
 
 static int
@@ -399,8 +403,10 @@ dtrace_getarg(int arg, int aframes)
 		goto load;
 	}
 
-	for (i = 1; i <= aframes; i++)
+	for (i = 1; i <= aframes; i++) {
+		kmsan_mark(fp, sizeof(*fp), KMSAN_STATE_INITED);
 		fp = fp->f_frame;
+	}
 
 	/*
 	 * We know that we did not come through a trap to get into
@@ -430,6 +436,8 @@ load:
 	val = stack[arg];
 	DTRACE_CPUFLAG_CLEAR(CPU_DTRACE_NOFAULT);
 
+	kmsan_mark(&val, sizeof(val), KMSAN_STATE_INITED);
+
 	return (val);
 }
 
@@ -444,10 +452,13 @@ dtrace_getstackdepth(int aframes)
 	rbp = dtrace_getfp();
 	frame = (struct amd64_frame *)rbp;
 	depth++;
-	for(;;) {
+	for (;;) {
+		kmsan_mark(frame, sizeof(*frame), KMSAN_STATE_INITED);
+
 		if (!kstack_contains(curthread, (vm_offset_t)frame,
 		    sizeof(*frame)))
 			break;
+
 		depth++;
 		if (frame->f_frame <= frame)
 			break;
@@ -574,76 +585,100 @@ void
 dtrace_copyin(uintptr_t uaddr, uintptr_t kaddr, size_t size,
     volatile uint16_t *flags)
 {
-	if (dtrace_copycheck(uaddr, kaddr, size))
+	if (dtrace_copycheck(uaddr, kaddr, size)) {
 		dtrace_copy(uaddr, kaddr, size);
+		kmsan_mark((void *)kaddr, size, KMSAN_STATE_INITED);
+	}
 }
 
 void
 dtrace_copyout(uintptr_t kaddr, uintptr_t uaddr, size_t size,
     volatile uint16_t *flags)
 {
-	if (dtrace_copycheck(uaddr, kaddr, size))
+	if (dtrace_copycheck(uaddr, kaddr, size)) {
+		kmsan_check((void *)kaddr, size, "dtrace_copyout");
 		dtrace_copy(kaddr, uaddr, size);
+	}
 }
 
 void
 dtrace_copyinstr(uintptr_t uaddr, uintptr_t kaddr, size_t size,
     volatile uint16_t *flags)
 {
-	if (dtrace_copycheck(uaddr, kaddr, size))
+	if (dtrace_copycheck(uaddr, kaddr, size)) {
 		dtrace_copystr(uaddr, kaddr, size, flags);
+		kmsan_mark((void *)kaddr, size, KMSAN_STATE_INITED);
+	}
 }
 
 void
 dtrace_copyoutstr(uintptr_t kaddr, uintptr_t uaddr, size_t size,
     volatile uint16_t *flags)
 {
-	if (dtrace_copycheck(uaddr, kaddr, size))
+	if (dtrace_copycheck(uaddr, kaddr, size)) {
+		kmsan_check((void *)kaddr, size, "dtrace_copyoutstr");
 		dtrace_copystr(kaddr, uaddr, size, flags);
+	}
 }
 
 uint8_t
 dtrace_fuword8(void *uaddr)
 {
+	uint8_t val;
+
 	if ((uintptr_t)uaddr > VM_MAXUSER_ADDRESS) {
 		DTRACE_CPUFLAG_SET(CPU_DTRACE_BADADDR);
 		cpu_core[curcpu].cpuc_dtrace_illval = (uintptr_t)uaddr;
 		return (0);
 	}
-	return (dtrace_fuword8_nocheck(uaddr));
+	val = dtrace_fuword8_nocheck(uaddr);
+	kmsan_mark(&val, sizeof(val), KMSAN_STATE_INITED);
+	return (val);
 }
 
 uint16_t
 dtrace_fuword16(void *uaddr)
 {
+	uint16_t val;
+
 	if ((uintptr_t)uaddr > VM_MAXUSER_ADDRESS) {
 		DTRACE_CPUFLAG_SET(CPU_DTRACE_BADADDR);
 		cpu_core[curcpu].cpuc_dtrace_illval = (uintptr_t)uaddr;
 		return (0);
 	}
-	return (dtrace_fuword16_nocheck(uaddr));
+	val = dtrace_fuword16_nocheck(uaddr);
+	kmsan_mark(&val, sizeof(val), KMSAN_STATE_INITED);
+	return (val);
 }
 
 uint32_t
 dtrace_fuword32(void *uaddr)
 {
+	uint32_t val;
+
 	if ((uintptr_t)uaddr > VM_MAXUSER_ADDRESS) {
 		DTRACE_CPUFLAG_SET(CPU_DTRACE_BADADDR);
 		cpu_core[curcpu].cpuc_dtrace_illval = (uintptr_t)uaddr;
 		return (0);
 	}
-	return (dtrace_fuword32_nocheck(uaddr));
+	val = dtrace_fuword32_nocheck(uaddr);
+	kmsan_mark(&val, sizeof(val), KMSAN_STATE_INITED);
+	return (val);
 }
 
 uint64_t
 dtrace_fuword64(void *uaddr)
 {
+	uint64_t val;
+
 	if ((uintptr_t)uaddr > VM_MAXUSER_ADDRESS) {
 		DTRACE_CPUFLAG_SET(CPU_DTRACE_BADADDR);
 		cpu_core[curcpu].cpuc_dtrace_illval = (uintptr_t)uaddr;
 		return (0);
 	}
-	return (dtrace_fuword64_nocheck(uaddr));
+	val = dtrace_fuword64_nocheck(uaddr);
+	kmsan_mark(&val, sizeof(val), KMSAN_STATE_INITED);
+	return (val);
 }
 
 /*
diff --git a/sys/cddl/dev/fbt/fbt.c b/sys/cddl/dev/fbt/fbt.c
index 481c896e977..99a77ba65eb 100644
--- a/sys/cddl/dev/fbt/fbt.c
+++ b/sys/cddl/dev/fbt/fbt.c
@@ -136,6 +136,13 @@ fbt_excluded(const char *name)
 	    strcmp(name, "owner_sx") == 0)
 		return (1);
 
+	/*
+	 * The KMSAN runtime can't be instrumented safely.
+	 */
+	if (strncmp(name, "__msan", 6) == 0 ||
+	    strncmp(name, "kmsan_", 6) == 0)
+		return (1);
+
 	/*
 	 * Stack unwinders may be called from probe context on some
 	 * platforms.
diff --git a/sys/cddl/dev/kinst/kinst.c b/sys/cddl/dev/kinst/kinst.c
index 60400a452b9..82b78d98987 100644
--- a/sys/cddl/dev/kinst/kinst.c
+++ b/sys/cddl/dev/kinst/kinst.c
@@ -132,6 +132,13 @@ kinst_excluded(const char *name)
 	    strcmp(name, "owner_sx") == 0)
 		return (true);
 
+	/*
+	 * The KMSAN runtime can't be instrumented safely.
+	 */
+	if (strncmp(name, "__msan", 6) == 0 ||
+	    strncmp(name, "kmsan_", 6) == 0)
+		return (1);
+
 	/*
 	 * When DTrace is built into the kernel we need to exclude the kinst
 	 * functions from instrumentation.