selftests/powerpc: Add test for execute-disabled pkeys

Apart from read and write access, memory protection keys can
also be used for restricting execute permission of pages on
powerpc. This adds a test to verify if the feature works as
expected.

Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200604125610.649668-4-sandipan@linux.ibm.com

tools/testing/selftests/powerpc/mm/.gitignore

@@ -8,3 +8,4 @@ wild_bctr
 large_vm_fork_separation
 bad_accesses
 tlbie_test
+pkey_exec_prot

tools/testing/selftests/powerpc/mm/Makefile

@@ -3,7 +3,7 @@ noarg:
 	$(MAKE) -C ../
 
 TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao segv_errors wild_bctr \
-		  large_vm_fork_separation bad_accesses
+		  large_vm_fork_separation bad_accesses pkey_exec_prot
 TEST_GEN_PROGS_EXTENDED := tlbie_test
 TEST_GEN_FILES := tempfile
 
@@ -17,6 +17,7 @@ $(OUTPUT)/prot_sao: ../utils.c
 $(OUTPUT)/wild_bctr: CFLAGS += -m64
 $(OUTPUT)/large_vm_fork_separation: CFLAGS += -m64
 $(OUTPUT)/bad_accesses: CFLAGS += -m64
+$(OUTPUT)/pkey_exec_prot: CFLAGS += -m64
 
 $(OUTPUT)/tempfile:
 	dd if=/dev/zero of=$@ bs=64k count=1