PAuth adds 5 different keys that can be used to sign addresses.
Add a test that verifies that the kernel initializes them uniquely and
preserves them across context switches.
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@xxxxxxx>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>
Signed-off-by: Boyan Karatotev <boyan.karatotev@xxxxxxx>
---
tools/testing/selftests/arm64/pauth/pac.c | 118 ++++++++++++++++++++++
1 file changed, 118 insertions(+)
diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c
index 1b9e3acfeb61..7d0ba2ec2e9e 100644
--- a/tools/testing/selftests/arm64/pauth/pac.c
+++ b/tools/testing/selftests/arm64/pauth/pac.c
@@ -1,10 +1,13 @@
// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2020 ARM Limited
+#define _GNU_SOURCE
+
#include <sys/auxv.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
+#include <sched.h>
#include "../../kselftest_harness.h"
#include "helper.h"
@@ -21,6 +24,7 @@
* The VA space size is 48 bits. Bigger is opt-in.
*/
#define PAC_MASK (~0xff80ffffffffffff)
+#define ARBITRARY_VALUE (0x1234)
#define ASSERT_PAUTH_ENABLED() \
do { \
unsigned long hwcaps = getauxval(AT_HWCAP); \
@@ -66,13 +70,36 @@ int are_same(struct signatures *old, struct signatures *new, int nkeys)
return res;
}
+int are_unique(struct signatures *sign, int nkeys)
+{
+ size_t vals[nkeys];
+
+ vals[0] = sign->keyia & PAC_MASK;
+ vals[1] = sign->keyib & PAC_MASK;
+ vals[2] = sign->keyda & PAC_MASK;
+ vals[3] = sign->keydb & PAC_MASK;
+
+ if (nkeys >= 4)
+ vals[4] = sign->keyg & PAC_MASK;
+
+ for (int i = 0; i < nkeys - 1; i++) {
+ for (int j = i + 1; j < nkeys; j++) {
+ if (vals[i] == vals[j])
+ return 0;
+ }
+ }
+ return 1;
+}
+
int exec_sign_all(struct signatures *signed_vals, size_t val)
{
int new_stdin[2];
int new_stdout[2];
int status;
+ int i;
ssize_t ret;
pid_t pid;
+ cpu_set_t mask;
ret = pipe(new_stdin);
if (ret == -1) {
@@ -86,6 +113,20 @@ int exec_sign_all(struct signatures *signed_vals, size_t val)
return -1;
}
+ /*
+ * pin this process and all its children to a single CPU, so it can also
+ * guarantee a context switch with its child
+ */
+ sched_getaffinity(0, sizeof(mask), &mask);
+
+ for (i = 0; i < sizeof(cpu_set_t); i++)
+ if (CPU_ISSET(i, &mask))
+ break;
+
+ CPU_ZERO(&mask);
+ CPU_SET(i, &mask);
+ sched_setaffinity(0, sizeof(mask), &mask);
+
pid = fork();
// child
if (pid == 0) {
@@ -192,6 +233,40 @@ TEST(pac_instructions_not_nop_generic)
ASSERT_NE(0, keyg) TH_LOG("keyg instructions did nothing");
}
+TEST(single_thread_unique_keys)
+{
+ int unique = 0;
+ int nkeys = NKEYS;
+ struct signatures signed_vals;
+ unsigned long hwcaps = getauxval(AT_HWCAP);
+
+ /* generic and data key instructions are not in NOP space. This prevents a SIGILL */
+ ASSERT_NE(0, hwcaps & HWCAP_PACA) TH_LOG("PAUTH not enabled");
+ if (!(hwcaps & HWCAP_PACG)) {
+ TH_LOG("WARNING: Generic PAUTH not enabled. Skipping generic key checks");
+ nkeys = NKEYS - 1;
+ }
+
+ /*
+ * In Linux the PAC field can be up to 7 bits wide. Even if keys are
+ * unique, there is about 5% chance for PACs to collide with different
+ * addresses. This chance rapidly increases with fewer bits allocated
+ * for the PAC (e.g. wider address). A comparison of the keys directly
+ * will be more reliable.
+ * All signed values need to be unique at least once out of n attempts
+ * to be certain that the keys are unique
+ */
+ for (int i = 0; i < PAC_COLLISION_ATTEMPTS; i++) {
+ if (nkeys == NKEYS)
+ sign_all(&signed_vals, i);
+ else
+ sign_specific(&signed_vals, i);
+ unique |= are_unique(&signed_vals, nkeys);
+ }
+
+ ASSERT_EQ(1, unique) TH_LOG("keys clashed every time");
+}
+
/*
* fork() does not change keys. Only exec() does so call a worker program.
* Its only job is to sign a value and report back the resutls
@@ -227,4 +302,47 @@ TEST(exec_unique_keys)
ASSERT_EQ(1, different) TH_LOG("exec() did not change keys");
}
+TEST(context_switch_keep_keys)
+{
+ int ret;
+ struct signatures trash;
+ struct signatures before;
+ struct signatures after;
+
+ ASSERT_PAUTH_ENABLED();
+
+ sign_specific(&before, ARBITRARY_VALUE);
+
+ /* will context switch with a process with different keys at least once */
+ ret = exec_sign_all(&trash, ARBITRARY_VALUE);
+ ASSERT_EQ(0, ret) TH_LOG("failed to run worker");
+
+ sign_specific(&after, ARBITRARY_VALUE);
+
+ ASSERT_EQ(before.keyia, after.keyia) TH_LOG("keyia changed after context switching");
+ ASSERT_EQ(before.keyib, after.keyib) TH_LOG("keyib changed after context switching");
+ ASSERT_EQ(before.keyda, after.keyda) TH_LOG("keyda changed after context switching");
+ ASSERT_EQ(before.keydb, after.keydb) TH_LOG("keydb changed after context switching");
+}
+
+TEST(context_switch_keep_keys_generic)
+{
+ int ret;
+ struct signatures trash;
+ size_t before;
+ size_t after;
+
+ ASSERT_GENERIC_PAUTH_ENABLED();
+
+ before = keyg_sign(ARBITRARY_VALUE);
+
+ /* will context switch with a process with different keys at least once */
+ ret = exec_sign_all(&trash, ARBITRARY_VALUE);
+ ASSERT_EQ(0, ret) TH_LOG("failed to run worker");
+
+ after = keyg_sign(ARBITRARY_VALUE);
+
+ ASSERT_EQ(before, after) TH_LOG("keyg changed after context switching");
+}
+
TEST_HARNESS_MAIN
--
2.17.1
