kselftests/arm64: add nop checks for PAuth tests

PAuth adds sign/verify controls to enable and disable groups of
instructions in hardware for compatibility with libraries that do not
implement PAuth. The kernel always enables them if it detects PAuth.

Add a test that checks that each group of instructions is enabled, if the
kernel reports PAuth as detected.

Note: For groups, for the purpose of this patch, we intend instructions
that use a certain key.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200918104715.182310-3-boian4o1@gmail.com
Signed-off-by: Will Deacon <will@kernel.org>

tools/testing/selftests/arm64/pauth/.gitignore

@@ -1 +1,2 @@
+exec_target
 pac

tools/testing/selftests/arm64/pauth/Makefile

@@ -12,7 +12,7 @@ pauth_cc_support := $(shell if ($(CC) $(CFLAGS) -march=armv8.3-a -E -x c /dev/nu
 
 ifeq ($(pauth_cc_support),1)
 TEST_GEN_PROGS := pac
-TEST_GEN_FILES := pac_corruptor.o
+TEST_GEN_FILES := pac_corruptor.o helper.o
 endif
 
 include ../../lib.mk
@@ -23,10 +23,13 @@ ifeq ($(pauth_cc_support),1)
 $(OUTPUT)/pac_corruptor.o: pac_corruptor.S
 	$(CC) -c $^ -o $@ $(CFLAGS) -march=armv8.3-a
 
+$(OUTPUT)/helper.o: helper.c
+	$(CC) -c $^ -o $@ $(CFLAGS) -march=armv8.3-a
+
 # when -mbranch-protection is enabled and the target architecture is ARMv8.3 or
 # greater, gcc emits pac* instructions which are not in HINT NOP space,
 # preventing the tests from occurring at all. Compile for ARMv8.2 so tests can
 # run on earlier targets and print a meaningful error messages
-$(OUTPUT)/pac: pac.c $(OUTPUT)/pac_corruptor.o
+$(OUTPUT)/pac: pac.c $(OUTPUT)/pac_corruptor.o $(OUTPUT)/helper.o
 	$(CC) $^ -o $@ $(CFLAGS) -march=armv8.2-a
 endif

tools/testing/selftests/arm64/pauth/helper.c

@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2020 ARM Limited
+
+#include "helper.h"
+
+size_t keyia_sign(size_t ptr)
+{
+	asm volatile("paciza %0" : "+r" (ptr));
+	return ptr;
+}
+
+size_t keyib_sign(size_t ptr)
+{
+	asm volatile("pacizb %0" : "+r" (ptr));
+	return ptr;
+}
+
+size_t keyda_sign(size_t ptr)
+{
+	asm volatile("pacdza %0" : "+r" (ptr));
+	return ptr;
+}
+
+size_t keydb_sign(size_t ptr)
+{
+	asm volatile("pacdzb %0" : "+r" (ptr));
+	return ptr;
+}
+
+size_t keyg_sign(size_t ptr)
+{
+	/* output is encoded in the upper 32 bits */
+	size_t dest = 0;
+	size_t modifier = 0;
+
+	asm volatile("pacga %0, %1, %2" : "=r" (dest) : "r" (ptr), "r" (modifier));
+
+	return dest;
+}

tools/testing/selftests/arm64/pauth/helper.h

@@ -4,6 +4,15 @@
 #ifndef _HELPER_H_
 #define _HELPER_H_
 
+#include <stdlib.h>
+
 void pac_corruptor(void);
 
+/* PAuth sign a value with key ia and modifier value 0 */
+size_t keyia_sign(size_t val);
+size_t keyib_sign(size_t val);
+size_t keyda_sign(size_t val);
+size_t keydb_sign(size_t val);
+size_t keyg_sign(size_t val);
+
 #endif

tools/testing/selftests/arm64/pauth/pac.c

@@ -8,12 +8,25 @@
 #include "../../kselftest_harness.h"
 #include "helper.h"
 
+#define PAC_COLLISION_ATTEMPTS 10
+/*
+ * The kernel sets TBID by default. So bits 55 and above should remain
+ * untouched no matter what.
+ * The VA space size is 48 bits. Bigger is opt-in.
+ */
+#define PAC_MASK (~0xff80ffffffffffff)
 #define ASSERT_PAUTH_ENABLED() \
 do { \
 	unsigned long hwcaps = getauxval(AT_HWCAP); \
 	/* data key instructions are not in NOP space. This prevents a SIGILL */ \
 	ASSERT_NE(0, hwcaps & HWCAP_PACA) TH_LOG("PAUTH not enabled"); \
 } while (0)
+#define ASSERT_GENERIC_PAUTH_ENABLED() \
+do { \
+	unsigned long hwcaps = getauxval(AT_HWCAP); \
+	/* generic key instructions are not in NOP space. This prevents a SIGILL */ \
+	ASSERT_NE(0, hwcaps & HWCAP_PACG) TH_LOG("Generic PAUTH not enabled"); \
+} while (0)
 
 sigjmp_buf jmpbuf;
 void pac_signal_handler(int signum, siginfo_t *si, void *uc)
@@ -41,4 +54,42 @@ TEST(corrupt_pac)
 	}
 }
 
+/*
+ * There are no separate pac* and aut* controls so checking only the pac*
+ * instructions is sufficient
+ */
+TEST(pac_instructions_not_nop)
+{
+	size_t keyia = 0;
+	size_t keyib = 0;
+	size_t keyda = 0;
+	size_t keydb = 0;
+
+	ASSERT_PAUTH_ENABLED();
+
+	for (int i = 0; i < PAC_COLLISION_ATTEMPTS; i++) {
+		keyia |= keyia_sign(i) & PAC_MASK;
+		keyib |= keyib_sign(i) & PAC_MASK;
+		keyda |= keyda_sign(i) & PAC_MASK;
+		keydb |= keydb_sign(i) & PAC_MASK;
+	}
+
+	ASSERT_NE(0, keyia) TH_LOG("keyia instructions did nothing");
+	ASSERT_NE(0, keyib) TH_LOG("keyib instructions did nothing");
+	ASSERT_NE(0, keyda) TH_LOG("keyda instructions did nothing");
+	ASSERT_NE(0, keydb) TH_LOG("keydb instructions did nothing");
+}
+
+TEST(pac_instructions_not_nop_generic)
+{
+	size_t keyg = 0;
+
+	ASSERT_GENERIC_PAUTH_ENABLED();
+
+	for (int i = 0; i < PAC_COLLISION_ATTEMPTS; i++)
+		keyg |= keyg_sign(i) & PAC_MASK;
+
+	ASSERT_NE(0, keyg)  TH_LOG("keyg instructions did nothing");
+}
+
 TEST_HARNESS_MAIN