linux-kernel - [PATCH 2/2] x86/selftests/pkeys: fork() to check for state being preserved

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Date:   Fri, 26 Oct 2018 12:51:47 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        peterz@...radead.org, mpe@...erman.id.au, will.deacon@....com,
        luto@...nel.org, jroedel@...e.de
Subject: [PATCH 2/2] x86/selftests/pkeys: fork() to check for state being preserved


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

There was a bug where the per-mm pkey state was not being preserved
across fork() in the child.  fork() is performed in the pkey
selftests, but all of our pkey activity is performed in the parent.
The child does not perform any actions sensitive to pkey state.

To make the test more sensitive to these kinds of bugs, add a
fork() where we let the parent exit, and continue execution in
the child.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Will Deacon <will.deacon@....com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Joerg Roedel <jroedel@...e.de>
---

 b/tools/testing/selftests/x86/protection_keys.c |   30 ++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff -puN tools/testing/selftests/x86/protection_keys.c~x86-pkeys-no-init-at-fork-selftests tools/testing/selftests/x86/protection_keys.c
--- a/tools/testing/selftests/x86/protection_keys.c~x86-pkeys-no-init-at-fork-selftests	2018-10-26 09:26:51.970102217 -0700
+++ b/tools/testing/selftests/x86/protection_keys.c	2018-10-26 09:26:51.974102217 -0700
@@ -1133,6 +1133,21 @@ void test_pkey_syscalls_bad_args(int *pt
 	pkey_assert(err);
 }
 
+void become_child(void)
+{
+	pid_t forkret;
+
+	forkret = fork();
+	pkey_assert(forkret >= 0);
+	dprintf3("[%d] fork() ret: %d\n", getpid(), forkret);
+
+	if (!forkret) {
+		/* in the child */
+		return;
+	}
+	exit(0);
+}
+
 /* Assumes that all pkeys other than 'pkey' are unallocated */
 void test_pkey_alloc_exhaust(int *ptr, u16 pkey)
 {
@@ -1141,7 +1156,7 @@ void test_pkey_alloc_exhaust(int *ptr, u
 	int nr_allocated_pkeys = 0;
 	int i;
 
-	for (i = 0; i < NR_PKEYS*2; i++) {
+	for (i = 0; i < NR_PKEYS*3; i++) {
 		int new_pkey;
 		dprintf1("%s() alloc loop: %d\n", __func__, i);
 		new_pkey = alloc_pkey();
@@ -1152,10 +1167,17 @@ void test_pkey_alloc_exhaust(int *ptr, u
 		if ((new_pkey == -1) && (errno == ENOSPC)) {
 			dprintf2("%s() failed to allocate pkey after %d tries\n",
 				__func__, nr_allocated_pkeys);
-			break;
+		} else {
+			pkey_assert(nr_allocated_pkeys < NR_PKEYS);
+			allocated_pkeys[nr_allocated_pkeys++] = new_pkey;
 		}
-		pkey_assert(nr_allocated_pkeys < NR_PKEYS);
-		allocated_pkeys[nr_allocated_pkeys++] = new_pkey;
+
+		/*
+		 * Make sure that allocation state is properly
+		 * preserved across fork().
+		 */
+		if (i == NR_PKEYS*2)
+			become_child();
 	}
 
 	dprintf3("%s()::%d\n", __func__, __LINE__);
_