x86/pkeys/selftests: Add PROT_EXEC test

Under the covers, implement executable-only memory with
protection keys when userspace calls mprotect(PROT_EXEC).

But, we did not have a selftest for that.  Now we do.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Michael Ellermen <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ram Pai <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

tools/testing/selftests/x86/protection_keys.c

@@ -1303,6 +1303,49 @@ void test_executing_on_unreadable_memory(int *ptr, u16 pkey)
 	expected_pk_fault(pkey);
 }
 
+void test_implicit_mprotect_exec_only_memory(int *ptr, u16 pkey)
+{
+	void *p1;
+	int scratch;
+	int ptr_contents;
+	int ret;
+
+	dprintf1("%s() start\n", __func__);
+
+	p1 = get_pointer_to_instructions();
+	lots_o_noops_around_write(&scratch);
+	ptr_contents = read_ptr(p1);
+	dprintf2("ptr (%p) contents@%d: %x\n", p1, __LINE__, ptr_contents);
+
+	/* Use a *normal* mprotect(), not mprotect_pkey(): */
+	ret = mprotect(p1, PAGE_SIZE, PROT_EXEC);
+	pkey_assert(!ret);
+
+	dprintf2("pkru: %x\n", rdpkru());
+
+	/* Make sure this is an *instruction* fault */
+	madvise(p1, PAGE_SIZE, MADV_DONTNEED);
+	lots_o_noops_around_write(&scratch);
+	do_not_expect_pk_fault("executing on PROT_EXEC memory");
+	ptr_contents = read_ptr(p1);
+	dprintf2("ptr (%p) contents@%d: %x\n", p1, __LINE__, ptr_contents);
+	expected_pk_fault(UNKNOWN_PKEY);
+
+	/*
+	 * Put the memory back to non-PROT_EXEC.  Should clear the
+	 * exec-only pkey off the VMA and allow it to be readable
+	 * again.  Go to PROT_NONE first to check for a kernel bug
+	 * that did not clear the pkey when doing PROT_NONE.
+	 */
+	ret = mprotect(p1, PAGE_SIZE, PROT_NONE);
+	pkey_assert(!ret);
+
+	ret = mprotect(p1, PAGE_SIZE, PROT_READ|PROT_EXEC);
+	pkey_assert(!ret);
+	ptr_contents = read_ptr(p1);
+	do_not_expect_pk_fault("plain read on recently PROT_EXEC area");
+}
+
 void test_mprotect_pkey_on_unsupported_cpu(int *ptr, u16 pkey)
 {
 	int size = PAGE_SIZE;
@@ -1327,6 +1370,7 @@ void (*pkey_tests[])(int *ptr, u16 pkey) = {
 	test_kernel_gup_of_access_disabled_region,
 	test_kernel_gup_write_to_write_disabled_region,
 	test_executing_on_unreadable_memory,
+	test_implicit_mprotect_exec_only_memory,
 	test_ptrace_of_child,
 	test_pkey_syscalls_on_non_allocated_pkey,
 	test_pkey_syscalls_bad_args,