linux-kernel - [PATCH 3/3] x86, pkeys, selftests: add a test for pkey 0

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Message-Id: <20180316214659.FCFEF68B@viggo.jf.intel.com>
Date:   Fri, 16 Mar 2018 14:46:59 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        linuxram@...ibm.com, tglx@...utronix.de, dave.hansen@...el.com,
        mpe@...erman.id.au, mingo@...nel.org, akpm@...ux-foundation.org,
        shuah@...nel.org
Subject: [PATCH 3/3] x86, pkeys, selftests: add a test for pkey 0


From: Dave Hansen <dave.hansen@...ux.intel.com>

Protection key 0 is the default key for all memory and will
not normally come back from pkey_alloc().  But, you might
still want pass it to mprotect_pkey().

This check ensures that you can use pkey 0.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Ram Pai <linuxram@...ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Michael Ellermen <mpe@...erman.id.au>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Shuah Khan <shuah@...nel.org>
---

 b/tools/testing/selftests/x86/protection_keys.c |   30 ++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff -puN tools/testing/selftests/x86/protection_keys.c~pkeys-update-selftests-with-pkey-0-test tools/testing/selftests/x86/protection_keys.c
--- a/tools/testing/selftests/x86/protection_keys.c~pkeys-update-selftests-with-pkey-0-test	2018-03-16 14:46:40.121285473 -0700
+++ b/tools/testing/selftests/x86/protection_keys.c	2018-03-16 14:46:40.125285473 -0700
@@ -1197,6 +1197,35 @@ void test_pkey_alloc_exhaust(int *ptr, u
 	}
 }
 
+/*
+ * pkey 0 is special.  It is allocated by default, so you do not
+ * have to call pkey_alloc() to use it first.  Make sure that it
+ * is usable.
+ */
+void test_mprotect_with_pkey_0(int *ptr, u16 pkey)
+{
+	long size;
+	int prot;
+
+	assert(pkey_last_malloc_record);
+	size = pkey_last_malloc_record->size;
+	/*
+	 * This is a bit of a hack.  But mprotect() requires
+	 * huge-page-aligned sizes when operating on hugetlbfs.
+	 * So, make sure that we use something that's a multiple
+	 * of a huge page when we can.
+	 */
+	if (size >= HPAGE_SIZE)
+		size = HPAGE_SIZE;
+	prot = pkey_last_malloc_record->prot;
+
+	/* Use pkey 0 */
+	mprotect_pkey(ptr, size, prot, 0);
+
+	/* Make sure that we can set it back to the original pkey. */
+	mprotect_pkey(ptr, size, prot, pkey);
+}
+
 void test_ptrace_of_child(int *ptr, u16 pkey)
 {
 	__attribute__((__unused__)) int peek_result;
@@ -1334,6 +1363,7 @@ 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_mprotect_with_pkey_0,
 	test_ptrace_of_child,
 	test_pkey_syscalls_on_non_allocated_pkey,
 	test_pkey_syscalls_bad_args,
_