IB/hfi1: Remove overly conservative VM_EXEC flag check

Applications that use the stack for execution purposes cause userspace PSM
jobs to fail during mmap().

Both Fortran (non-standard format parsing) and C (callback functions
located in the stack) applications can be written such that stack
execution is required. The linker notes this via the gnu_stack ELF flag.

This causes READ_IMPLIES_EXEC to be set which forces all PROT_READ mmaps
to have PROT_EXEC for the process.

Checking for VM_EXEC bit and failing the request with EPERM is overly
conservative and will break any PSM application using executable stacks.

Cc: <stable@vger.kernel.org> #v4.14+
Fixes: 12220267 ("IB/hfi: Protect against writable mmap")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hfi1/file_ops.c

@@ -488,7 +488,7 @@ static int hfi1_file_mmap(struct file *fp, struct vm_area_struct *vma)
 		vmf = 1;
 		break;
 	case STATUS:
-		if (flags & (unsigned long)(VM_WRITE | VM_EXEC)) {
+		if (flags & VM_WRITE) {
 			ret = -EPERM;
 			goto done;
 		}