Date:   Fri, 28 Aug 2020 14:16:05 +0100
From:   Boyan Karatotev <boyan.karatotev@....com>
To:     linux-arm-kernel@...ts.infradead.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     vincenzo.frascino@....com, amit.kachhap@....com,
        boian4o1@...il.com, Boyan Karatotev <boyan.karatotev@....com>,
        Shuah Khan <shuah@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: [PATCH 3/4] kselftests/arm64: add PAuth test for whether exec() changes keys

Kernel documentation states that it will change PAuth keys on exec() calls.

Verify that all keys are correctly switched to new ones.

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/Makefile  |   4 +
 .../selftests/arm64/pauth/exec_target.c       |  35 +++++
 tools/testing/selftests/arm64/pauth/helper.h  |  10 ++
 tools/testing/selftests/arm64/pauth/pac.c     | 148 ++++++++++++++++++
 4 files changed, 197 insertions(+)
 create mode 100644 tools/testing/selftests/arm64/pauth/exec_target.c

diff --git a/tools/testing/selftests/arm64/pauth/Makefile b/tools/testing/selftests/arm64/pauth/Makefile
index a017d1c8dd58..2e237b21ccf6 100644
--- a/tools/testing/selftests/arm64/pauth/Makefile
+++ b/tools/testing/selftests/arm64/pauth/Makefile
@@ -5,6 +5,7 @@ CFLAGS += -mbranch-protection=pac-ret
 
 TEST_GEN_PROGS := pac
 TEST_GEN_FILES := pac_corruptor.o helper.o
+TEST_GEN_PROGS_EXTENDED := exec_target
 
 include ../../lib.mk
 
@@ -20,6 +21,9 @@ $(OUTPUT)/helper.o: helper.c
 # greater, gcc emits pac* instructions which are not in HINT NOP space,
 # preventing the tests from occurring at all. Compile for ARMv8.2 so tests can
 # run on earlier targets and print a meaningful error messages
+$(OUTPUT)/exec_target: exec_target.c $(OUTPUT)/helper.o
+	$(CC) $^ -o $@ $(CFLAGS) -march=armv8.2-a
+
 $(OUTPUT)/pac: pac.c $(OUTPUT)/pac_corruptor.o $(OUTPUT)/helper.o
 	$(CC) $^ -o $@ $(CFLAGS) -march=armv8.2-a
 
diff --git a/tools/testing/selftests/arm64/pauth/exec_target.c b/tools/testing/selftests/arm64/pauth/exec_target.c
new file mode 100644
index 000000000000..07addef5a1d7
--- /dev/null
+++ b/tools/testing/selftests/arm64/pauth/exec_target.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2020 ARM Limited
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/auxv.h>
+
+#include "helper.h"
+
+
+int main(void)
+{
+	struct signatures signed_vals;
+	unsigned long hwcaps;
+	size_t val;
+
+	fread(&val, sizeof(size_t), 1, stdin);
+
+	/* don't try to execute illegal (unimplemented) instructions) caller
+	 * should have checked this and keep worker simple
+	 */
+	hwcaps = getauxval(AT_HWCAP);
+
+	if (hwcaps & HWCAP_PACA) {
+		signed_vals.keyia = keyia_sign(val);
+		signed_vals.keyib = keyib_sign(val);
+		signed_vals.keyda = keyda_sign(val);
+		signed_vals.keydb = keydb_sign(val);
+	}
+	signed_vals.keyg = (hwcaps & HWCAP_PACG) ?  keyg_sign(val) : 0;
+
+	fwrite(&signed_vals, sizeof(struct signatures), 1, stdout);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/arm64/pauth/helper.h b/tools/testing/selftests/arm64/pauth/helper.h
index b3cf709e249d..fceaa1e4824a 100644
--- a/tools/testing/selftests/arm64/pauth/helper.h
+++ b/tools/testing/selftests/arm64/pauth/helper.h
@@ -6,6 +6,16 @@
 
 #include <stdlib.h>
 
+#define NKEYS 5
+
+
+struct signatures {
+	size_t keyia;
+	size_t keyib;
+	size_t keyda;
+	size_t keydb;
+	size_t keyg;
+};
 
 void pac_corruptor(void);
 
diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c
index cdbffa8bf61e..16dea47b11c7 100644
--- a/tools/testing/selftests/arm64/pauth/pac.c
+++ b/tools/testing/selftests/arm64/pauth/pac.c
@@ -2,6 +2,8 @@
 // Copyright (C) 2020 ARM Limited
 
 #include <sys/auxv.h>
+#include <sys/types.h>
+#include <sys/wait.h>
 #include <signal.h>
 
 #include "../../kselftest_harness.h"
@@ -33,6 +35,117 @@ do { \
 } while (0)
 
 
+void sign_specific(struct signatures *sign, size_t val)
+{
+	sign->keyia = keyia_sign(val);
+	sign->keyib = keyib_sign(val);
+	sign->keyda = keyda_sign(val);
+	sign->keydb = keydb_sign(val);
+}
+
+void sign_all(struct signatures *sign, size_t val)
+{
+	sign->keyia = keyia_sign(val);
+	sign->keyib = keyib_sign(val);
+	sign->keyda = keyda_sign(val);
+	sign->keydb = keydb_sign(val);
+	sign->keyg  = keyg_sign(val);
+}
+
+int are_same(struct signatures *old, struct signatures *new, int nkeys)
+{
+	int res = 0;
+
+	res |= old->keyia == new->keyia;
+	res |= old->keyib == new->keyib;
+	res |= old->keyda == new->keyda;
+	res |= old->keydb == new->keydb;
+	if (nkeys == NKEYS)
+		res |= old->keyg  == new->keyg;
+
+	return res;
+}
+
+int exec_sign_all(struct signatures *signed_vals, size_t val)
+{
+	int new_stdin[2];
+	int new_stdout[2];
+	int status;
+	ssize_t ret;
+	pid_t pid;
+
+	ret = pipe(new_stdin);
+	if (ret == -1) {
+		perror("pipe returned error");
+		return -1;
+	}
+
+	ret = pipe(new_stdout);
+	if (ret == -1) {
+		perror("pipe returned error");
+		return -1;
+	}
+
+	pid = fork();
+	// child
+	if (pid == 0) {
+		dup2(new_stdin[0], STDIN_FILENO);
+		if (ret == -1) {
+			perror("dup2 returned error");
+			exit(1);
+		}
+
+		dup2(new_stdout[1], STDOUT_FILENO);
+		if (ret == -1) {
+			perror("dup2 returned error");
+			exit(1);
+		}
+
+		close(new_stdin[0]);
+		close(new_stdin[1]);
+		close(new_stdout[0]);
+		close(new_stdout[1]);
+
+		ret = execl("exec_target", "exec_target", (char *) NULL);
+		if (ret == -1) {
+			perror("exec returned error");
+			exit(1);
+		}
+	}
+
+	close(new_stdin[0]);
+	close(new_stdout[1]);
+
+	ret = write(new_stdin[1], &val, sizeof(size_t));
+	if (ret == -1) {
+		perror("write returned error");
+		return -1;
+	}
+
+	/*
+	 * wait for the worker to finish, so that read() reads all data
+	 * will also context switch with worker so that this function can be used
+	 * for context switch tests
+	 */
+	waitpid(pid, &status, 0);
+	if (WIFEXITED(status) == 0) {
+		fprintf(stderr, "worker exited unexpectedly\n");
+		return -1;
+	}
+	if (WEXITSTATUS(status) != 0) {
+		fprintf(stderr, "worker exited with error\n");
+		return -1;
+	}
+
+	ret = read(new_stdout[0], signed_vals, sizeof(struct signatures));
+	if (ret == -1) {
+		perror("read returned error");
+		return -1;
+	}
+
+	return 0;
+}
+
 /* check that a corrupted PAC results in SIGSEGV */
 TEST_SIGNAL(corrupt_pac, SIGSEGV)
 {
@@ -79,5 +192,40 @@ TEST(pac_instructions_not_nop_generic)
 	ASSERT_NE(0, keyg)  TH_LOG("keyg instructions did nothing");
 }
 
+/*
+ * 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
+ */
+TEST(exec_unique_keys)
+{
+	struct signatures new_keys;
+	struct signatures old_keys;
+	int ret;
+	int different = 0;
+	int nkeys = NKEYS;
+	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;
+	}
+
+	for (int i = 0; i < PAC_COLLISION_ATTEMPTS; i++) {
+		ret = exec_sign_all(&new_keys, i);
+		ASSERT_EQ(0, ret) TH_LOG("failed to run worker");
+
+		if (nkeys == NKEYS)
+			sign_all(&old_keys, i);
+		else
+			sign_specific(&old_keys, i);
+
+		different |= !are_same(&old_keys, &new_keys, nkeys);
+	}
+
+	ASSERT_EQ(1, different) TH_LOG("exec() did not change keys");
+}
+
 TEST_HARNESS_MAIN
 
-- 
2.17.1

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