[PATCH] hugetlb: permit executable mappings

During the kernel summit, some discussion was had about the support
requirements for a userspace program loader that loads executables into
hugetlb on behalf of a major application (Oracle).  In order to support
this in a robust fashion, the cleanup of the hugetlb must be robust in the
presence of disorderly termination of the programs (e.g.  kill -9).  Hence,
the cleanup semantics are those of System V shared memory, but Linux'
System V shared memory needs one critical extension for this use:
executability.

The following microscopic patch enables this major application to provide
robust hugetlb cleanup.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/shm.h

@@ -44,6 +44,7 @@ struct shmid_ds {
 #define	SHM_RDONLY	010000	/* read-only access */
 #define	SHM_RND		020000	/* round attach address to SHMLBA boundary */
 #define	SHM_REMAP	040000	/* take-over region on attach */
+#define	SHM_EXEC	0100000	/* execution access */
 
 /* super user shmctl commands */
 #define SHM_LOCK 	11

ipc/shm.c

@@ -688,6 +688,10 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
 		o_flags = O_RDWR;
 		acc_mode = S_IRUGO | S_IWUGO;
 	}
+	if (shmflg & SHM_EXEC) {
+		prot |= PROT_EXEC;
+		acc_mode |= S_IXUGO;
+	}
 
 	/*
 	 * We cannot rely on the fs check since SYSV IPC does have an