From: Boyan Karatotev boyan.karatotev@arm.com
PAuth adds 5 different keys that can be used to sign addresses.
Add a test that verifies that the kernel initializes them to different values and preserves them across context switches.
Cc: Shuah Khan shuah@kernel.org Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will@kernel.org Reviewed-by: Vincenzo Frascino Vincenzo.Frascino@arm.com Reviewed-by: Amit Daniel Kachhap amit.kachhap@arm.com Acked-by: Shuah Khan skhan@linuxfoundation.org Signed-off-by: Boyan Karatotev boyan.karatotev@arm.com --- tools/testing/selftests/arm64/pauth/pac.c | 123 ++++++++++++++++++++++ 1 file changed, 123 insertions(+)
diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c index b363ad6a0b50..592fe538506e 100644 --- a/tools/testing/selftests/arm64/pauth/pac.c +++ b/tools/testing/selftests/arm64/pauth/pac.c @@ -1,11 +1,14 @@ // 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 <setjmp.h> +#include <sched.h>
#include "../../kselftest_harness.h" #include "helper.h" @@ -17,6 +20,7 @@ * 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); \ @@ -61,13 +65,37 @@ int n_same(struct signatures *old, struct signatures *new, int nkeys) return res; }
+int n_same_single_set(struct signatures *sign, int nkeys) +{ + size_t vals[nkeys]; + int same = 0; + + 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]) + same += 1; + } + } + return same; +} + 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) { @@ -81,6 +109,20 @@ 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) { @@ -205,6 +247,44 @@ TEST(pac_instructions_not_nop_generic) ASSERT_NE(0, keyg) TH_LOG("keyg instructions did nothing"); }
+TEST(single_thread_different_keys) +{ + int same = 10; + int nkeys = NKEYS; + int tmp; + 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 + * different, 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 different at least once out of n + * attempts to be certain that the keys are different + */ + for (int i = 0; i < PAC_COLLISION_ATTEMPTS; i++) { + if (nkeys == NKEYS) + sign_all(&signed_vals, i); + else + sign_specific(&signed_vals, i); + + tmp = n_same_single_set(&signed_vals, nkeys); + if (tmp < same) + same = tmp; + } + + ASSERT_EQ(0, same) TH_LOG("%d keys clashed every time", same); +} + /* * 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 @@ -242,4 +322,47 @@ TEST(exec_changed_keys) ASSERT_EQ(0, same) TH_LOG("exec() did not change %d keys", same); }
+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