Make UMA and malloc(9) return non-executable memory in most cases.

Most kernel memory that is allocated after boot does not need to be
executable.  There are a few exceptions.  For example, kernel modules
do need executable memory, but they don't use UMA or malloc(9).  The
BPF JIT compiler also needs executable memory and did use malloc(9)
until r317072.

(Note that a side effect of r316767 was that the "small allocation"
path in UMA on amd64 already returned non-executable memory.  This
meant that some calls to malloc(9) or the UMA zone(9) allocator could
return executable memory, while others could return non-executable
memory.  This change makes the behavior consistent.)

This change makes malloc(9) return non-executable memory unless the new
M_EXEC flag is specified.  After this change, the UMA zone(9) allocator
will always return non-executable memory, and a KASSERT will catch
attempts to use the M_EXEC flag to allocate executable memory using
uma_zalloc() or its variants.

Allocations that do need executable memory have various choices.  They
may use the M_EXEC flag to malloc(9), or they may use a different VM
interfact to obtain executable pages.

Now that malloc(9) again allows executable allocations, this change also
reverts most of r317072.

PR:		228927
Reviewed by:	alc, kib, markj, jhb (previous version)
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D15691

16 files changed, 142 insertions, 62 deletions

diff --git a/share/man/man9/malloc.9 b/share/man/man9/malloc.9
index 82294a6897f5..26ea111641c2 100644
--- a/share/man/man9/malloc.9
+++ b/share/man/man9/malloc.9
@@ -29,7 +29,7 @@
 .\" $NetBSD: malloc.9,v 1.3 1996/11/11 00:05:11 lukem Exp $
 .\" $FreeBSD$
 .\"
-.Dd January 24, 2018
+.Dd June 13, 2018
 .Dt MALLOC 9
 .Os
 .Sh NAME
@@ -189,6 +189,11 @@ This option should only be used in combination with
 .Dv M_NOWAIT
 when an allocation failure cannot be tolerated by the caller without
 catastrophic effects on the system.
+.It Dv M_EXEC
+Indicates that the system should allocate executable memory.
+If this flag is not set, the system will not allocate executable memory.
+Not all platforms enforce a distinction between executable and
+non-executable memory.
 .El
 .Pp
 Exactly one of either
diff --git a/share/man/man9/zone.9 b/share/man/man9/zone.9
index 0e8d7838e193..76dea4bae189 100644
--- a/share/man/man9/zone.9
+++ b/share/man/man9/zone.9
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 26, 2017
+.Dd June 13, 2018
 .Dt ZONE 9
 .Os
 .Sh NAME
@@ -375,6 +375,15 @@ if the zone ran out of unused items
 and
 .Dv M_NOWAIT
 was specified.
+.Sh IMPLEMENTATION NOTES
+The memory that these allocation calls return is not executable.
+The
+.Fn uma_zalloc
+function does not support the
+.Dv M_EXEC
+flag to allocate executable memory.
+Not all platforms enforce a distinction between executable and
+non-executable memory.
 .Sh SEE ALSO
 .Xr malloc 9
 .Sh HISTORY
diff --git a/sys/amd64/amd64/bpf_jit_machdep.c b/sys/amd64/amd64/bpf_jit_machdep.c
index 8d4ddaa24135..d65978e9c84c 100644
--- a/sys/amd64/amd64/bpf_jit_machdep.c
+++ b/sys/amd64/amd64/bpf_jit_machdep.c
@@ -44,9 +44,6 @@ __FBSDID("$FreeBSD$");
 #include <sys/socket.h>
 
 #include <net/if.h>
-#include <vm/vm.h>
-#include <vm/vm_extern.h>
-#include <vm/vm_kern.h>
 #else
 #include <stdlib.h>
 #include <string.h>
@@ -605,11 +602,7 @@ bpf_jit_compile(struct bpf_insn *prog, u_int nins, size_t *size)
 
 		*size = stream.cur_ip;
 #ifdef _KERNEL
-		/*
-		 * We cannot use malloc(9) because DMAP is mapped as NX.
-		 */
-		stream.ibuf = (void *)kmem_malloc(kernel_arena, *size,
-		    M_NOWAIT);
+		stream.ibuf = malloc(*size, M_BPFJIT, M_EXEC | M_NOWAIT);
 		if (stream.ibuf == NULL)
 			break;
 #else
@@ -658,14 +651,3 @@ bpf_jit_compile(struct bpf_insn *prog, u_int nins, size_t *size)
 
 	return ((bpf_filter_func)(void *)stream.ibuf);
 }
-
-void
-bpf_jit_free(void *func, size_t size)
-{
-
-#ifdef _KERNEL
-	kmem_free(kernel_arena, (vm_offset_t)func, size);
-#else
-	munmap(func, size);
-#endif
-}
diff --git a/sys/i386/i386/bpf_jit_machdep.c b/sys/i386/i386/bpf_jit_machdep.c
index ff3fa3fb0750..6d77d0ba6f30 100644
--- a/sys/i386/i386/bpf_jit_machdep.c
+++ b/sys/i386/i386/bpf_jit_machdep.c
@@ -632,7 +632,7 @@ bpf_jit_compile(struct bpf_insn *prog, u_int nins, size_t *size)
 
 		*size = stream.cur_ip;
 #ifdef _KERNEL
-		stream.ibuf = malloc(*size, M_BPFJIT, M_NOWAIT);
+		stream.ibuf = malloc(*size, M_BPFJIT, M_EXEC | M_NOWAIT);
 		if (stream.ibuf == NULL)
 			break;
 #else
@@ -681,14 +681,3 @@ bpf_jit_compile(struct bpf_insn *prog, u_int nins, size_t *size)
 
 	return ((bpf_filter_func)(void *)stream.ibuf);
 }
-
-void
-bpf_jit_free(void *func, size_t size)
-{
-
-#ifdef _KERNEL
-	free(func, M_BPFJIT);
-#else
-	munmap(func, size);
-#endif
-}
diff --git a/sys/kern/kern_malloc.c b/sys/kern/kern_malloc.c
index 50dfe2507b62..3bc0e6ee0d11 100644
--- a/sys/kern/kern_malloc.c
+++ b/sys/kern/kern_malloc.c
@@ -564,7 +564,7 @@ void *
 		return (va);
 #endif
 
-	if (size <= kmem_zmax) {
+	if (size <= kmem_zmax && (flags & M_EXEC) == 0) {
 		if (size & KMEM_ZMASK)
 			size = (size & ~KMEM_ZMASK) + KMEM_ZBASE;
 		indx = kmemsize[size >> KMEM_ZSHIFT];
@@ -609,7 +609,7 @@ malloc_domain(size_t size, struct malloc_type *mtp, int domain,
 	if (malloc_dbg(&va, &size, mtp, flags) != 0)
 		return (va);
 #endif
-	if (size <= kmem_zmax) {
+	if (size <= kmem_zmax && (flags & M_EXEC) == 0) {
 		if (size & KMEM_ZMASK)
 			size = (size & ~KMEM_ZMASK) + KMEM_ZBASE;
 		indx = kmemsize[size >> KMEM_ZSHIFT];
diff --git a/sys/kern/subr_vmem.c b/sys/kern/subr_vmem.c
index 6e6ce3ee6b2c..92da3f9a8577 100644
--- a/sys/kern/subr_vmem.c
+++ b/sys/kern/subr_vmem.c
@@ -241,6 +241,9 @@ static struct vmem buffer_arena_storage;
 static struct vmem transient_arena_storage;
 /* kernel and kmem arenas are aliased for backwards KPI compat. */
 vmem_t *kernel_arena = &kernel_arena_storage;
+#if VM_NRESERVLEVEL > 0
+vmem_t *kernel_rwx_arena = NULL;
+#endif
 vmem_t *kmem_arena = &kernel_arena_storage;
 vmem_t *buffer_arena = &buffer_arena_storage;
 vmem_t *transient_arena = &transient_arena_storage;
diff --git a/sys/net/bpf_jitter.c b/sys/net/bpf_jitter.c
index 276c10dd57fb..abe7bfa465fd 100644
--- a/sys/net/bpf_jitter.c
+++ b/sys/net/bpf_jitter.c
@@ -101,11 +101,13 @@ void
 bpf_destroy_jit_filter(bpf_jit_filter *filter)
 {
 
-	if (filter->func != bpf_jit_accept_all)
-		bpf_jit_free(filter->func, filter->size);
 #ifdef _KERNEL
+	if (filter->func != bpf_jit_accept_all)
+		free(filter->func, M_BPFJIT);
 	free(filter, M_BPFJIT);
 #else
+	if (filter->func != bpf_jit_accept_all)
+		munmap(filter->func, filter->size);
 	free(filter);
 #endif
 }
diff --git a/sys/net/bpf_jitter.h b/sys/net/bpf_jitter.h
index a7c7cd9f7320..23049d148567 100644
--- a/sys/net/bpf_jitter.h
+++ b/sys/net/bpf_jitter.h
@@ -88,6 +88,5 @@ void		bpf_destroy_jit_filter(bpf_jit_filter *filter);
 struct bpf_insn;
 
 bpf_filter_func	bpf_jit_compile(struct bpf_insn *, u_int, size_t *);
-void		bpf_jit_free(void *, size_t);
 
 #endif	/* _NET_BPF_JITTER_H_ */
diff --git a/sys/sys/malloc.h b/sys/sys/malloc.h
index c8edd207cdcc..e9908f558a19 100644
--- a/sys/sys/malloc.h
+++ b/sys/sys/malloc.h
@@ -49,7 +49,7 @@
 #define	MINALLOCSIZE	UMA_SMALLEST_UNIT
 
 /*
- * flags to malloc.
+ * Flags to memory allocation functions.
  */
 #define	M_NOWAIT	0x0001		/* do not block */
 #define	M_WAITOK	0x0002		/* ok to block */
@@ -59,6 +59,7 @@
 #define	M_NODUMP	0x0800		/* don't dump pages in this allocation */
 #define	M_FIRSTFIT	0x1000		/* Only for vmem, fast fit. */
 #define	M_BESTFIT	0x2000		/* Only for vmem, low fragmentation. */
+#define	M_EXEC		0x4000		/* allocate executable space. */
 
 #define	M_MAGIC		877983977	/* time when first defined :-) */
 
diff --git a/sys/vm/uma.h b/sys/vm/uma.h
index 9fe51e515f4a..ed33ae030728 100644
--- a/sys/vm/uma.h
+++ b/sys/vm/uma.h
@@ -617,11 +617,12 @@ void uma_zone_set_freef(uma_zone_t zone, uma_free freef);
  * These flags are setable in the allocf and visible in the freef.
  */
 #define UMA_SLAB_BOOT	0x01		/* Slab alloced from boot pages */
+#define UMA_SLAB_KRWX	0x02		/* Slab alloced from kernel_rwx_arena */
 #define UMA_SLAB_KERNEL	0x04		/* Slab alloced from kernel_map */
 #define UMA_SLAB_PRIV	0x08		/* Slab alloced from priv allocator */
 #define UMA_SLAB_OFFP	0x10		/* Slab is managed separately  */
 #define UMA_SLAB_MALLOC	0x20		/* Slab is a large malloc slab */
-/* 0x02, 0x40 and 0x80 are available */
+/* 0x40 and 0x80 are available */
 
 /*
  * Used to pre-fill a zone with some number of items
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index c44b10cd3f14..16a702cb4aa7 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -1167,7 +1167,7 @@ page_alloc(uma_zone_t zone, vm_size_t bytes, int domain, uint8_t *pflag,
 	void *p;	/* Returned page */
 
 	*pflag = UMA_SLAB_KERNEL;
-	p = (void *) kmem_malloc_domain(domain, bytes, wait);
+	p = (void *) kmem_malloc_domain(kernel_arena, domain, bytes, wait);
 
 	return (p);
 }
@@ -2280,6 +2280,7 @@ uma_zalloc_arg(uma_zone_t zone, void *udata, int flags)
 		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
 		    "uma_zalloc_arg: zone \"%s\"", zone->uz_name);
 	}
+	KASSERT((flags & M_EXEC) == 0, ("uma_zalloc_arg: called with M_EXEC"));
 	KASSERT(curthread->td_critnest == 0 || SCHEDULER_STOPPED(),
 	    ("uma_zalloc_arg: called with spinlock or critical section held"));
 	if (zone->uz_flags & UMA_ZONE_PCPU)
@@ -3587,20 +3588,34 @@ uma_zone_exhausted_nolock(uma_zone_t zone)
 void *
 uma_large_malloc_domain(vm_size_t size, int domain, int wait)
 {
+	struct vmem *arena;
 	vm_offset_t addr;
 	uma_slab_t slab;
 
+#if VM_NRESERVLEVEL > 0
+	if (__predict_true((wait & M_EXEC) == 0))
+		arena = kernel_arena;
+	else
+		arena = kernel_rwx_arena;
+#else
+	arena = kernel_arena;
+#endif
+
 	slab = zone_alloc_item(slabzone, NULL, domain, wait);
 	if (slab == NULL)
 		return (NULL);
 	if (domain == UMA_ANYDOMAIN)
-		addr = kmem_malloc(kernel_arena, size, wait);
+		addr = kmem_malloc(arena, size, wait);
 	else
-		addr = kmem_malloc_domain(domain, size, wait);
+		addr = kmem_malloc_domain(arena, domain, size, wait);
 	if (addr != 0) {
 		vsetslab(addr, slab);
 		slab->us_data = (void *)addr;
 		slab->us_flags = UMA_SLAB_KERNEL | UMA_SLAB_MALLOC;
+#if VM_NRESERVLEVEL > 0
+		if (__predict_false(arena == kernel_rwx_arena))
+			slab->us_flags |= UMA_SLAB_KRWX;
+#endif
 		slab->us_size = size;
 		slab->us_domain = vm_phys_domain(PHYS_TO_VM_PAGE(
 		    pmap_kextract(addr)));
@@ -3622,10 +3637,19 @@ uma_large_malloc(vm_size_t size, int wait)
 void
 uma_large_free(uma_slab_t slab)
 {
+	struct vmem *arena;
 
 	KASSERT((slab->us_flags & UMA_SLAB_KERNEL) != 0,
 	    ("uma_large_free:  Memory not allocated with uma_large_malloc."));
-	kmem_free(kernel_arena, (vm_offset_t)slab->us_data, slab->us_size);
+#if VM_NRESERVLEVEL > 0
+	if (__predict_true((slab->us_flags & UMA_SLAB_KRWX) == 0))
+		arena = kernel_arena;
+	else
+		arena = kernel_rwx_arena;
+#else
+	arena = kernel_arena;
+#endif
+	kmem_free(arena, (vm_offset_t)slab->us_data, slab->us_size);
 	uma_total_dec(slab->us_size);
 	zone_free_item(slabzone, slab, NULL, SKIP_NONE);
 }
diff --git a/sys/vm/vm_extern.h b/sys/vm/vm_extern.h
index fde50f4a26ef..22f945b197dc 100644
--- a/sys/vm/vm_extern.h
+++ b/sys/vm/vm_extern.h
@@ -65,7 +65,8 @@ vm_offset_t kmem_alloc_contig_domain(int domain, vm_size_t size, int flags,
     vm_paddr_t low, vm_paddr_t high, u_long alignment, vm_paddr_t boundary,
     vm_memattr_t memattr);
 vm_offset_t kmem_malloc(struct vmem *, vm_size_t size, int flags);
-vm_offset_t kmem_malloc_domain(int domain, vm_size_t size, int flags);
+vm_offset_t kmem_malloc_domain(struct vmem *, int domain, vm_size_t size,
+    int flags);
 void kmem_free(struct vmem *, vm_offset_t, vm_size_t);
 
 /* This provides memory for previously allocated address space. */
diff --git a/sys/vm/vm_init.c b/sys/vm/vm_init.c
index 0b721d0acce9..0a1af123ddbc 100644
--- a/sys/vm/vm_init.c
+++ b/sys/vm/vm_init.c
@@ -135,6 +135,23 @@ kva_import(void *unused, vmem_size_t size, int flags, vmem_addr_t *addrp)
 	return (0);
 }
 
+#if VM_NRESERVLEVEL > 0
+/*
+ * Import a superpage from the normal kernel arena into the special
+ * arena for allocations with different permissions.
+ */
+static int
+kernel_rwx_alloc(void *arena, vmem_size_t size, int flags, vmem_addr_t *addrp)
+{
+
+	KASSERT((size % KVA_QUANTUM) == 0,
+	    ("kernel_rwx_alloc: Size %jd is not a multiple of %d",
+	    (intmax_t)size, (int)KVA_QUANTUM));
+	return (vmem_xalloc(arena, size, KVA_QUANTUM, 0, 0, VMEM_ADDR_MIN,
+	    VMEM_ADDR_MAX, flags, addrp));
+}
+#endif
+
 /*
  *	vm_init initializes the virtual memory system.
  *	This is done only by the first cpu up.
@@ -173,12 +190,31 @@ vm_mem_init(dummy)
 	vmem_init(kernel_arena, "kernel arena", 0, 0, PAGE_SIZE, 0, 0);
 	vmem_set_import(kernel_arena, kva_import, NULL, NULL, KVA_QUANTUM);
 
+#if VM_NRESERVLEVEL > 0
+	/*
+	 * In an architecture with superpages, maintain a separate arena
+	 * for allocations with permissions that differ from the "standard"
+	 * read/write permissions used for memory in the kernel_arena.
+	 */
+	kernel_rwx_arena = vmem_create("kernel rwx arena", 0, 0, PAGE_SIZE,
+	    0, M_WAITOK);
+	vmem_set_import(kernel_rwx_arena, kernel_rwx_alloc,
+	    (vmem_release_t *)vmem_xfree, kernel_arena, KVA_QUANTUM);
+#endif
+
 	for (domain = 0; domain < vm_ndomains; domain++) {
 		vm_dom[domain].vmd_kernel_arena = vmem_create(
 		    "kernel arena domain", 0, 0, PAGE_SIZE, 0, M_WAITOK);
 		vmem_set_import(vm_dom[domain].vmd_kernel_arena,
 		    (vmem_import_t *)vmem_alloc, NULL, kernel_arena,
 		    KVA_QUANTUM);
+#if VM_NRESERVLEVEL > 0
+		vm_dom[domain].vmd_kernel_rwx_arena = vmem_create(
+		    "kernel rwx arena domain", 0, 0, PAGE_SIZE, 0, M_WAITOK);
+		vmem_set_import(vm_dom[domain].vmd_kernel_rwx_arena,
+		    kernel_rwx_alloc, (vmem_release_t *)vmem_xfree,
+		    vm_dom[domain].vmd_kernel_arena, KVA_QUANTUM);
+#endif
 	}
 
 #ifndef	UMA_MD_SMALL_ALLOC
diff --git a/sys/vm/vm_kern.c b/sys/vm/vm_kern.c
index 0ff1b155c069..037db5723396 100644
--- a/sys/vm/vm_kern.c
+++ b/sys/vm/vm_kern.c
@@ -212,8 +212,8 @@ retry:
 		if ((flags & M_ZERO) && (m->flags & PG_ZERO) == 0)
 			pmap_zero_page(m);
 		m->valid = VM_PAGE_BITS_ALL;
-		pmap_enter(kernel_pmap, addr + i, m, VM_PROT_ALL,
-		    VM_PROT_ALL | PMAP_ENTER_WIRED, 0);
+		pmap_enter(kernel_pmap, addr + i, m, VM_PROT_RW,
+		    VM_PROT_RW | PMAP_ENTER_WIRED, 0);
 	}
 	VM_OBJECT_WUNLOCK(object);
 	return (addr);
@@ -298,8 +298,8 @@ retry:
 		if ((flags & M_ZERO) && (m->flags & PG_ZERO) == 0)
 			pmap_zero_page(m);
 		m->valid = VM_PAGE_BITS_ALL;
-		pmap_enter(kernel_pmap, tmp, m, VM_PROT_ALL,
-		    VM_PROT_ALL | PMAP_ENTER_WIRED, 0);
+		pmap_enter(kernel_pmap, tmp, m, VM_PROT_RW,
+		    VM_PROT_RW | PMAP_ENTER_WIRED, 0);
 		tmp += PAGE_SIZE;
 	}
 	VM_OBJECT_WUNLOCK(object);
@@ -372,20 +372,32 @@ kmem_suballoc(vm_map_t parent, vm_offset_t *min, vm_offset_t *max,
  *	Allocate wired-down pages in the kernel's address space.
  */
 vm_offset_t
-kmem_malloc_domain(int domain, vm_size_t size, int flags)
+kmem_malloc_domain(struct vmem *vmem, int domain, vm_size_t size, int flags)
 {
-	vmem_t *vmem;
+	vmem_t *arena;
 	vm_offset_t addr;
 	int rv;
 
-	vmem = vm_dom[domain].vmd_kernel_arena;
+#if VM_NRESERVLEVEL > 0
+	KASSERT(vmem == kernel_arena || vmem == kernel_rwx_arena,
+	    ("kmem_malloc_domain: Only kernel_arena or kernel_rwx_arena "
+	    "are supported."));
+	if (__predict_true(vmem == kernel_arena))
+		arena = vm_dom[domain].vmd_kernel_arena;
+	else
+		arena = vm_dom[domain].vmd_kernel_rwx_arena;
+#else
+	KASSERT(vmem == kernel_arena,
+	    ("kmem_malloc_domain: Only kernel_arena is supported."));
+	arena = vm_dom[domain].vmd_kernel_arena;
+#endif
 	size = round_page(size);
-	if (vmem_alloc(vmem, size, flags | M_BESTFIT, &addr))
+	if (vmem_alloc(arena, size, flags | M_BESTFIT, &addr))
 		return (0);
 
 	rv = kmem_back_domain(domain, kernel_object, addr, size, flags);
 	if (rv != KERN_SUCCESS) {
-		vmem_free(vmem, addr, size);
+		vmem_free(arena, addr, size);
 		return (0);
 	}
 	return (addr);
@@ -398,12 +410,9 @@ kmem_malloc(struct vmem *vmem, vm_size_t size, int flags)
 	vm_offset_t addr;
 	int domain;
 
-	KASSERT(vmem == kernel_arena,
-	    ("kmem_malloc: Only kernel_arena is supported."));
-
 	vm_domainset_iter_malloc_init(&di, kernel_object, &domain, &flags);
 	do {
-		addr = kmem_malloc_domain(domain, size, flags);
+		addr = kmem_malloc_domain(vmem, domain, size, flags);
 		if (addr != 0)
 			break;
 	} while (vm_domainset_iter_malloc(&di, &domain, &flags) == 0);
@@ -422,6 +431,7 @@ kmem_back_domain(int domain, vm_object_t object, vm_offset_t addr,
 {
 	vm_offset_t offset, i;
 	vm_page_t m, mpred;
+	vm_prot_t prot;
 	int pflags;
 
 	KASSERT(object == kernel_object,
@@ -432,6 +442,7 @@ kmem_back_domain(int domain, vm_object_t object, vm_offset_t addr,
 	pflags &= ~(VM_ALLOC_NOWAIT | VM_ALLOC_WAITOK | VM_ALLOC_WAITFAIL);
 	if (flags & M_WAITOK)
 		pflags |= VM_ALLOC_WAITFAIL;
+	prot = (flags & M_EXEC) != 0 ? VM_PROT_ALL : VM_PROT_RW;
 
 	i = 0;
 	VM_OBJECT_WLOCK(object);
@@ -461,8 +472,8 @@ retry:
 		KASSERT((m->oflags & VPO_UNMANAGED) != 0,
 		    ("kmem_malloc: page %p is managed", m));
 		m->valid = VM_PAGE_BITS_ALL;
-		pmap_enter(kernel_pmap, addr + i, m, VM_PROT_ALL,
-		    VM_PROT_ALL | PMAP_ENTER_WIRED, 0);
+		pmap_enter(kernel_pmap, addr + i, m, prot,
+		    prot | PMAP_ENTER_WIRED, 0);
 	}
 	VM_OBJECT_WUNLOCK(object);
 
@@ -542,13 +553,28 @@ kmem_unback(vm_object_t object, vm_offset_t addr, vm_size_t size)
 void
 kmem_free(struct vmem *vmem, vm_offset_t addr, vm_size_t size)
 {
+	struct vmem *arena;
 	int domain;
 
+#if VM_NRESERVLEVEL > 0
+	KASSERT(vmem == kernel_arena || vmem == kernel_rwx_arena,
+	    ("kmem_free: Only kernel_arena or kernel_rwx_arena are supported."));
+#else
 	KASSERT(vmem == kernel_arena,
 	    ("kmem_free: Only kernel_arena is supported."));
+#endif
+
 	size = round_page(size);
 	domain = _kmem_unback(kernel_object, addr, size);
-	vmem_free(vm_dom[domain].vmd_kernel_arena, addr, size);
+#if VM_NRESERVLEVEL > 0
+	if (__predict_true(vmem == kernel_arena))
+		arena = vm_dom[domain].vmd_kernel_arena;
+	else
+		arena = vm_dom[domain].vmd_kernel_rwx_arena;
+#else
+	arena = vm_dom[domain].vmd_kernel_arena;
+#endif
+	vmem_free(arena, addr, size);
 }
 
 /*
diff --git a/sys/vm/vm_kern.h b/sys/vm/vm_kern.h
index 20e847f5e5af..8d49a598f26d 100644
--- a/sys/vm/vm_kern.h
+++ b/sys/vm/vm_kern.h
@@ -70,6 +70,7 @@ extern vm_map_t kernel_map;
 extern vm_map_t exec_map;
 extern vm_map_t pipe_map;
 extern struct vmem *kernel_arena;
+extern struct vmem *kernel_rwx_arena;
 extern struct vmem *kmem_arena;
 extern struct vmem *buffer_arena;
 extern struct vmem *transient_arena;
diff --git a/sys/vm/vm_pagequeue.h b/sys/vm/vm_pagequeue.h
index a53e0a5f6791..fb56bdf2fdfc 100644
--- a/sys/vm/vm_pagequeue.h
+++ b/sys/vm/vm_pagequeue.h
@@ -103,7 +103,8 @@ struct vm_domain {
 	struct mtx_padalign vmd_free_mtx;
 	struct mtx_padalign vmd_pageout_mtx;
 	uma_zone_t vmd_pgcache;		/* (c) page free cache. */
-	struct vmem *vmd_kernel_arena;	/* (c) per-domain kva arena. */
+	struct vmem *vmd_kernel_arena;	/* (c) per-domain kva R/W arena. */
+	struct vmem *vmd_kernel_rwx_arena; /* (c) per-domain kva R/W/X arena. */
 	u_int vmd_domain;		/* (c) Domain number. */
 	u_int vmd_page_count;		/* (c) Total page count. */
 	long vmd_segs;			/* (c) bitmask of the segments */