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

1 files changed, 2 insertions, 1 deletions

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