Index: lib/libc/gen/sched_getaffinity.c
===================================================================
--- lib/libc/gen/sched_getaffinity.c
+++ lib/libc/gen/sched_getaffinity.c
@@ -33,24 +33,15 @@
 int
 sched_getaffinity(pid_t pid, size_t cpusetsz, cpuset_t *cpuset)
 {
-	/*
-	 * Be more Linux-compatible:
-	 * - return EINVAL in passed size is less than size of cpuset_t
-	 *   in advance, instead of ERANGE from the syscall
-	 * - if passed size is larger than the size of cpuset_t, be
-	 *   permissive by claming it back to sizeof(cpuset_t) and
-	 *   zeroing the rest.
-	 */
-	if (cpusetsz < sizeof(cpuset_t)) {
+	int error;
+
+	error = cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID,
+	    pid == 0 ? -1 : pid, cpusetsz, cpuset);
+	if (error == -1 && errno == ERANGE)
 		errno = EINVAL;
-		return (-1);
-	}
-	if (cpusetsz > sizeof(cpuset_t)) {
-		memset((char *)cpuset + sizeof(cpuset_t), 0,
-		    cpusetsz - sizeof(cpuset_t));
-		cpusetsz = sizeof(cpuset_t);
-	}
+	if (error == 0)
+		return (cpusetsz < sizeof(cpuset_t) ? cpusetsz :
+		    sizeof(cpuset_t));
 
-	return (cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID,
-	    pid == 0 ? -1 : pid, cpusetsz, cpuset));
+	return (error);
 }
Index: lib/libc/gen/sched_setaffinity.c
===================================================================
--- lib/libc/gen/sched_setaffinity.c
+++ lib/libc/gen/sched_setaffinity.c
@@ -33,18 +33,10 @@
 int
 sched_setaffinity(pid_t pid, size_t cpusetsz, const cpuset_t *cpuset)
 {
-	cpuset_t c;
 	int error;
 
-	if (cpusetsz > sizeof(cpuset_t)) {
-		errno = EINVAL;
-		return (-1);
-	} else {
-		memset(&c, 0, sizeof(c));
-		memcpy(&c, cpuset, cpusetsz);
-	}
 	error = cpuset_setaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID,
-	    pid == 0 ? -1 : pid, sizeof(cpuset_t), &c);
+	    pid == 0 ? -1 : pid, cpusetsz, cpuset);
 	if (error == -1 && errno == EDEADLK)
 		errno = EINVAL;
 
Index: lib/libc/sys/cpuset_getaffinity.2
===================================================================
--- lib/libc/sys/cpuset_getaffinity.2
+++ lib/libc/sys/cpuset_getaffinity.2
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 23, 2017
+.Dd April 27, 2022
 .Dt CPUSET_GETAFFINITY 2
 .Os
 .Sh NAME
@@ -71,14 +71,19 @@
 are composed using the
 .Dv CPU_SET
 macros.
-The kernel tolerates large sets as long as all CPUs specified
-in the set exist.
-Sets smaller than the kernel uses generate an error on calls to
+If the user-supplied mask is not large enough to fit all of the matching CPUs,
 .Fn cpuset_getaffinity
-even if the result set would fit within the user supplied set.
+fails with
+.Er ERANGE .
 Calls to
 .Fn cpuset_setaffinity
-tolerate small sets with no restrictions.
+tolerate masks of any size with no restrictions.
+The kernel uses a meaningful part of the mask, where the upper bound is
+the maximum CPU id present in the system.
+If bits for non-existing CPUs are set, calls to
+.Fn cpuset_setaffinity
+fails with
+.Er EINVAL .
 .Pp
 The supplied mask should have a size of
 .Fa setsize
@@ -144,7 +149,7 @@
 .It Bq Er ERANGE
 The
 .Fa cpusetsize
-was either preposterously large or smaller than the kernel set size.
+was smaller than needed to fit all of the matching CPUs.
 .It Bq Er EPERM
 The calling process did not have the credentials required to complete the
 operation.
Index: share/man/man3/pthread_attr_affinity_np.3
===================================================================
--- share/man/man3/pthread_attr_affinity_np.3
+++ share/man/man3/pthread_attr_affinity_np.3
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd October 12, 2021
+.Dd April 27, 2022
 .Dt PTHREAD_ATTR_AFFINITY_NP 3
 .Os
 .Sh NAME
@@ -51,14 +51,19 @@
 are composed using the
 .Dv CPU_SET
 macros.
-The kernel tolerates large sets as long as all CPUs specified
-in the set exist.
-Sets smaller than the kernel uses generate an error on calls to
-.Fn pthread_attr_getaffinity_np
-even if the result set would fit within the user supplied set.
+If the user-supplied mask is not large enough to fit all of the matching CPUs,
+.Fn cpuset_getaffinity
+fails with
+.Er ERANGE .
 Calls to
-.Fn pthread_attr_setaffinity_np
-tolerate small sets with no restrictions.
+.Fn cpuset_setaffinity
+tolerate masks of any size with no restrictions.
+The kernel uses a meaningful part of the mask, where the upper bound is
+the maximum CPU id present in the system.
+If bits for non-existing CPUs are set, calls to
+.Fn cpuset_setaffinity
+fails with
+.Er EINVAL .
 .Pp
 The supplied mask should have a size of
 .Fa cpusetsize
@@ -119,10 +124,6 @@
 The
 .Fa cpusetp
 specified a CPU that was outside the set supported by the kernel.
-.It Bq Er ERANGE
-The
-.Fa cpusetsize
-is too small.
 .It Bq Er ENOMEM
 Insufficient memory exists to store the cpuset mask.
 .El
Index: sys/kern/kern_cpuset.c
===================================================================
--- sys/kern/kern_cpuset.c
+++ sys/kern/kern_cpuset.c
@@ -1896,13 +1896,10 @@
 	int error;
 	size_t size;
 
-	if (cpusetsize < sizeof(cpuset_t) || cpusetsize > CPU_MAXSIZE / NBBY)
-		return (ERANGE);
 	error = cpuset_check_capabilities(td, level, which, id);
 	if (error != 0)
 		return (error);
-	size = cpusetsize;
-	mask = malloc(size, M_TEMP, M_WAITOK | M_ZERO);
+	mask = malloc(sizeof(cpuset_t), M_TEMP, M_WAITOK | M_ZERO);
 	error = cpuset_which(which, id, &p, &ttd, &set);
 	if (error)
 		goto out;
@@ -1972,8 +1969,33 @@
 		cpuset_rel(set);
 	if (p)
 		PROC_UNLOCK(p);
-	if (error == 0)
+	if (error == 0) {
+		if (cpusetsize < howmany(CPU_FLS(mask), NBBY)) {
+			error = ERANGE;
+			goto out;
+		}
+		size = min(cpusetsize, sizeof(cpuset_t));
 		error = copyout(mask, maskp, size);
+		if (error != 0)
+			goto out;
+		if (cpusetsize > size) {
+			char *end;
+			char *cp;
+			int rv;
+
+			end = cp = (char *)&maskp->__bits;
+			end += cpusetsize;
+			cp += size;
+			while (cp != end) {
+				rv = subyte(cp, 0);
+				if (rv == -1) {
+					error = EFAULT;
+					goto out;
+				}
+				cp++;
+			}
+		}
+	}
 out:
 	free(mask, M_TEMP);
 	return (error);
@@ -2006,31 +2028,38 @@
 	struct proc *p;
 	cpuset_t *mask;
 	int error;
+	size_t size;
 
-	if (cpusetsize < sizeof(cpuset_t) || cpusetsize > CPU_MAXSIZE / NBBY)
-		return (ERANGE);
 	error = cpuset_check_capabilities(td, level, which, id);
 	if (error != 0)
 		return (error);
-	mask = malloc(cpusetsize, M_TEMP, M_WAITOK | M_ZERO);
-	error = copyin(maskp, mask, cpusetsize);
+	size = min(cpusetsize, sizeof(cpuset_t));
+	mask = malloc(sizeof(cpuset_t), M_TEMP, M_WAITOK | M_ZERO);
+	error = copyin(maskp, mask, size);
 	if (error)
 		goto out;
 	/*
 	 * Verify that no high bits are set.
 	 */
 	if (cpusetsize > sizeof(cpuset_t)) {
-		char *end;
-		char *cp;
-
-		end = cp = (char *)&mask->__bits;
+		const char *end, *cp;
+		int val;
+		end = cp = (const char *)&maskp->__bits;
 		end += cpusetsize;
 		cp += sizeof(cpuset_t);
-		while (cp != end)
-			if (*cp++ != 0) {
+
+		while (cp != end) {
+			val = fubyte(cp);
+			if (val == -1) {
+				error = EFAULT;
+				goto out;
+			}
+			if (val != 0) {
 				error = EINVAL;
 				goto out;
 			}
+			cp++;
+		}
 	}
 	if (CPU_EMPTY(mask)) {
 		error = EDEADLK;