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Message-ID: <5c6622cb-e81f-c175-8150-b14009877468@arm.com>
Date: Fri, 28 Aug 2020 15:36:43 +0100
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: Boyan Karatotev <boyan.karatotev@....com>,
linux-arm-kernel@...ts.infradead.org,
linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: amit.kachhap@....com, boian4o1@...il.com,
Shuah Khan <shuah@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>
Subject: Re: [PATCH 4/4] kselftests/arm64: add PAuth tests for single threaded
consistency and key uniqueness
On 8/28/20 2:16 PM, Boyan Karatotev wrote:
> 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.
>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@....com>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Boyan Karatotev <boyan.karatotev@....com>
> ---
> tools/testing/selftests/arm64/pauth/pac.c | 116 ++++++++++++++++++++++
> 1 file changed, 116 insertions(+)
>
> diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c
> index 16dea47b11c7..718f49adc275 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 +233,38 @@ 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;
> + }
> +
> + /*
> + * The PAC field is up to 7 bits. Even with unique keys there is about
> + * 5% chance for a collision. This chance rapidly increases the fewer
> + * bits there are, 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
> @@ -227,5 +300,48 @@ 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
>
>
--
Regards,
Vincenzo
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