Pointer Authentication (PAuth) is a security feature introduced in ARMv8.3. It introduces instructions to sign addresses and later check for potential corruption using a second modifier value and one of a set of keys. The signature, in the form of the Pointer Authentication Code (PAC), is stored in some of the top unused bits of the virtual address (e.g. [54: 49] if TBID0 is enabled and TnSZ is set to use a 48 bit VA space). A set of controls are present to enable/disable groups of instructions (which use certain keys) for compatibility with libraries that do not utilize the feature. PAuth is used to verify the integrity of return addresses on the stack with less memory than the stack canary.
This patchset adds kselftests to verify the kernel's configuration of the feature and its runtime behaviour. There are 7 tests which verify that: * an authentication failure leads to a SIGSEGV * the data/instruction instruction groups are enabled * the generic instructions are enabled * all 5 keys are different for a single thread * exec() changes all keys to new different ones * context switching preserves the 4 data/instruction keys * context switching preserves the generic keys
The tests have been verified to work on qemu without a working PAUTH Implementation and on ARM's FVP with a full or partial PAuth implementation.
Changes in v3: * remove double blank lines * Patch 1: "kselftests: add a basic arm64 Pointer Authentication test" * shorten pac_corruptor.S to cut out unnecessary code * add second signal handler to cover ARMv8.6 compatibily * Patch 3: "kselftests/arm64: add PAuth test for whether exec() changes keys" * change name of "exec_unique_keys" to "exec_changed_keys" * change reporting of error to be how many keys were left unchanged * Path 4: "kselftests/arm64: add PAuth tests for single threaded consistency and key uniqueness" * change unique to different * rename "single_thread_unique_keys" to "single_thread_different_keys" * change reporting of error to be how many keys were left unchanged
Changes in v2: * remove extra lines at end of files * Patch 1: "kselftests: add a basic arm64 Pointer Authentication test" * add checks for a compatible compiler in Makefile * Patch 4: "kselftests: add PAuth tests for single threaded consistency and key uniqueness" * rephrase comment for clarity in pac.c
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 Signed-off-by: Boyan Karatotev boyan.karatotev@arm.com Acked-by: Shuah Khan skhan@linuxfoundation.org
Boyan Karatotev (4): kselftests/arm64: add a basic Pointer Authentication test kselftests/arm64: add nop checks for PAuth tests kselftests/arm64: add PAuth test for whether exec() changes keys kselftests/arm64: add PAuth tests for single threaded consistency and differently initialized keys
tools/testing/selftests/arm64/Makefile | 2 +- .../testing/selftests/arm64/pauth/.gitignore | 2 + tools/testing/selftests/arm64/pauth/Makefile | 39 ++ .../selftests/arm64/pauth/exec_target.c | 34 ++ tools/testing/selftests/arm64/pauth/helper.c | 39 ++ tools/testing/selftests/arm64/pauth/helper.h | 28 ++ tools/testing/selftests/arm64/pauth/pac.c | 368 ++++++++++++++++++ .../selftests/arm64/pauth/pac_corruptor.S | 19 + 8 files changed, 530 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/arm64/pauth/.gitignore create mode 100644 tools/testing/selftests/arm64/pauth/Makefile create mode 100644 tools/testing/selftests/arm64/pauth/exec_target.c create mode 100644 tools/testing/selftests/arm64/pauth/helper.c create mode 100644 tools/testing/selftests/arm64/pauth/helper.h create mode 100644 tools/testing/selftests/arm64/pauth/pac.c create mode 100644 tools/testing/selftests/arm64/pauth/pac_corruptor.S
-- 2.28.0
From: Boyan Karatotev boyan.karatotev@arm.com
PAuth signs and verifies return addresses on the stack. It does so by inserting a Pointer Authentication code (PAC) into some of the unused top bits of an address. This is achieved by adding paciasp/autiasp instructions at the beginning and end of a function.
This feature is partially backwards compatible with earlier versions of the ARM architecture. To coerce the compiler into emitting fully backwards compatible code the main file is compiled to target an earlier ARM version. This allows the tests to check for the feature and print meaningful error messages instead of crashing.
Add a test to verify that corrupting the return address results in a SIGSEGV on return.
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/Makefile | 2 +- .../testing/selftests/arm64/pauth/.gitignore | 1 + tools/testing/selftests/arm64/pauth/Makefile | 32 ++++++++++++++ tools/testing/selftests/arm64/pauth/helper.h | 9 ++++ tools/testing/selftests/arm64/pauth/pac.c | 44 +++++++++++++++++++ .../selftests/arm64/pauth/pac_corruptor.S | 19 ++++++++ 6 files changed, 106 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/arm64/pauth/.gitignore create mode 100644 tools/testing/selftests/arm64/pauth/Makefile create mode 100644 tools/testing/selftests/arm64/pauth/helper.h create mode 100644 tools/testing/selftests/arm64/pauth/pac.c create mode 100644 tools/testing/selftests/arm64/pauth/pac_corruptor.S
diff --git a/tools/testing/selftests/arm64/Makefile b/tools/testing/selftests/arm64/Makefile index 93b567d23c8b..525506fd97b9 100644 --- a/tools/testing/selftests/arm64/Makefile +++ b/tools/testing/selftests/arm64/Makefile @@ -4,7 +4,7 @@ ARCH ?= $(shell uname -m 2>/dev/null || echo not)
ifneq (,$(filter $(ARCH),aarch64 arm64)) -ARM64_SUBTARGETS ?= tags signal +ARM64_SUBTARGETS ?= tags signal pauth else ARM64_SUBTARGETS := endif diff --git a/tools/testing/selftests/arm64/pauth/.gitignore b/tools/testing/selftests/arm64/pauth/.gitignore new file mode 100644 index 000000000000..b557c916720a --- /dev/null +++ b/tools/testing/selftests/arm64/pauth/.gitignore @@ -0,0 +1 @@ +pac diff --git a/tools/testing/selftests/arm64/pauth/Makefile b/tools/testing/selftests/arm64/pauth/Makefile new file mode 100644 index 000000000000..01d35aaa610a --- /dev/null +++ b/tools/testing/selftests/arm64/pauth/Makefile @@ -0,0 +1,32 @@ +# SPDX-License-Identifier: GPL-2.0 +# Copyright (C) 2020 ARM Limited + +# preserve CC value from top level Makefile +ifeq ($(CC),cc) +CC := $(CROSS_COMPILE)gcc +endif + +CFLAGS += -mbranch-protection=pac-ret +# check if the compiler supports ARMv8.3 and branch protection with PAuth +pauth_cc_support := $(shell if ($(CC) $(CFLAGS) -march=armv8.3-a -E -x c /dev/null -o /dev/null 2>&1) then echo "1"; fi) + +ifeq ($(pauth_cc_support),1) +TEST_GEN_PROGS := pac +TEST_GEN_FILES := pac_corruptor.o +endif + +include ../../lib.mk + +ifeq ($(pauth_cc_support),1) +# pac* and aut* instructions are not available on architectures berfore +# ARMv8.3. Therefore target ARMv8.3 wherever they are used directly +$(OUTPUT)/pac_corruptor.o: pac_corruptor.S + $(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 + $(CC) $^ -o $@ $(CFLAGS) -march=armv8.2-a +endif diff --git a/tools/testing/selftests/arm64/pauth/helper.h b/tools/testing/selftests/arm64/pauth/helper.h new file mode 100644 index 000000000000..3e0a2a404bf4 --- /dev/null +++ b/tools/testing/selftests/arm64/pauth/helper.h @@ -0,0 +1,9 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* Copyright (C) 2020 ARM Limited */ + +#ifndef _HELPER_H_ +#define _HELPER_H_ + +void pac_corruptor(void); + +#endif diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c new file mode 100644 index 000000000000..0293310ba70a --- /dev/null +++ b/tools/testing/selftests/arm64/pauth/pac.c @@ -0,0 +1,44 @@ +// SPDX-License-Identifier: GPL-2.0 +// Copyright (C) 2020 ARM Limited + +#include <sys/auxv.h> +#include <signal.h> +#include <setjmp.h> + +#include "../../kselftest_harness.h" +#include "helper.h" + +#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) + +sigjmp_buf jmpbuf; +void pac_signal_handler(int signum, siginfo_t *si, void *uc) +{ + if (signum == SIGSEGV || signum == SIGILL) + siglongjmp(jmpbuf, 1); +} + +/* check that a corrupted PAC results in SIGSEGV or SIGILL */ +TEST(corrupt_pac) +{ + struct sigaction sa; + + ASSERT_PAUTH_ENABLED(); + if (sigsetjmp(jmpbuf, 1) == 0) { + sa.sa_sigaction = pac_signal_handler; + sa.sa_flags = SA_SIGINFO | SA_RESETHAND; + sigemptyset(&sa.sa_mask); + + sigaction(SIGSEGV, &sa, NULL); + sigaction(SIGILL, &sa, NULL); + + pac_corruptor(); + ASSERT_TRUE(0) TH_LOG("SIGSEGV/SIGILL signal did not occur"); + } +} + +TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/arm64/pauth/pac_corruptor.S b/tools/testing/selftests/arm64/pauth/pac_corruptor.S new file mode 100644 index 000000000000..aa6588050752 --- /dev/null +++ b/tools/testing/selftests/arm64/pauth/pac_corruptor.S @@ -0,0 +1,19 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* Copyright (C) 2020 ARM Limited */ + +.global pac_corruptor + +.text +/* + * Corrupting a single bit of the PAC ensures the authentication will fail. It + * also guarantees no possible collision. TCR_EL1.TBI0 is set by default so no + * top byte PAC is tested + */ + pac_corruptor: + paciasp + + /* corrupt the top bit of the PAC */ + eor lr, lr, #1 << 53 + + autiasp + ret
From: Boyan Karatotev boyan.karatotev@arm.com
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.
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 --- .../testing/selftests/arm64/pauth/.gitignore | 1 + tools/testing/selftests/arm64/pauth/Makefile | 7 ++- tools/testing/selftests/arm64/pauth/helper.c | 39 ++++++++++++++ tools/testing/selftests/arm64/pauth/helper.h | 9 ++++ tools/testing/selftests/arm64/pauth/pac.c | 51 +++++++++++++++++++ 5 files changed, 105 insertions(+), 2 deletions(-) create mode 100644 tools/testing/selftests/arm64/pauth/helper.c
diff --git a/tools/testing/selftests/arm64/pauth/.gitignore b/tools/testing/selftests/arm64/pauth/.gitignore index b557c916720a..155137d92722 100644 --- a/tools/testing/selftests/arm64/pauth/.gitignore +++ b/tools/testing/selftests/arm64/pauth/.gitignore @@ -1 +1,2 @@ +exec_target pac diff --git a/tools/testing/selftests/arm64/pauth/Makefile b/tools/testing/selftests/arm64/pauth/Makefile index 01d35aaa610a..5c0dd129562f 100644 --- a/tools/testing/selftests/arm64/pauth/Makefile +++ b/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 diff --git a/tools/testing/selftests/arm64/pauth/helper.c b/tools/testing/selftests/arm64/pauth/helper.c new file mode 100644 index 000000000000..2c201e7d0d50 --- /dev/null +++ b/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; +} diff --git a/tools/testing/selftests/arm64/pauth/helper.h b/tools/testing/selftests/arm64/pauth/helper.h index 3e0a2a404bf4..35c4f3357ae3 100644 --- a/tools/testing/selftests/arm64/pauth/helper.h +++ b/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 diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c index 0293310ba70a..bd3d4c0eca9d 100644 --- a/tools/testing/selftests/arm64/pauth/pac.c +++ b/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
From: Boyan Karatotev boyan.karatotev@arm.com
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@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/Makefile | 4 + .../selftests/arm64/pauth/exec_target.c | 34 ++++ tools/testing/selftests/arm64/pauth/helper.h | 10 ++ tools/testing/selftests/arm64/pauth/pac.c | 150 ++++++++++++++++++ 4 files changed, 198 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 5c0dd129562f..72e290b0b10c 100644 --- a/tools/testing/selftests/arm64/pauth/Makefile +++ b/tools/testing/selftests/arm64/pauth/Makefile @@ -13,6 +13,7 @@ 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 helper.o +TEST_GEN_PROGS_EXTENDED := exec_target endif
include ../../lib.mk @@ -30,6 +31,9 @@ $(OUTPUT)/helper.o: helper.c # greater, gcc emits pac* instructions which are not in HINT NOP space, # preventing the tests from occurring at all. Compile for ARMv8.2 so tests can # run on earlier targets and print a meaningful error messages +$(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 endif 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..4435600ca400 --- /dev/null +++ b/tools/testing/selftests/arm64/pauth/exec_target.c @@ -0,0 +1,34 @@ +// 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 35c4f3357ae3..652496c7b411 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);
/* PAuth sign a value with key ia and modifier value 0 */ diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c index bd3d4c0eca9d..b363ad6a0b50 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 <setjmp.h>
@@ -28,6 +30,117 @@ do { \ ASSERT_NE(0, hwcaps & HWCAP_PACG) TH_LOG("Generic PAUTH not enabled"); \ } 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 n_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; +} + sigjmp_buf jmpbuf; void pac_signal_handler(int signum, siginfo_t *si, void *uc) { @@ -92,4 +205,41 @@ 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_changed_keys) +{ + struct signatures new_keys; + struct signatures old_keys; + int ret; + int same = 10; + 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); + + ret = n_same(&old_keys, &new_keys, nkeys); + if (ret < same) + same = ret; + } + + ASSERT_EQ(0, same) TH_LOG("exec() did not change %d keys", same); +} + TEST_HARNESS_MAIN
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
On Fri, 18 Sep 2020 11:47:11 +0100, Boyan Karatotev wrote:
Pointer Authentication (PAuth) is a security feature introduced in ARMv8.3. It introduces instructions to sign addresses and later check for potential corruption using a second modifier value and one of a set of keys. The signature, in the form of the Pointer Authentication Code (PAC), is stored in some of the top unused bits of the virtual address (e.g. [54: 49] if TBID0 is enabled and TnSZ is set to use a 48 bit VA space). A set of controls are present to enable/disable groups of instructions (which use certain keys) for compatibility with libraries that do not utilize the feature. PAuth is used to verify the integrity of return addresses on the stack with less memory than the stack canary.
[...]
Applied to arm64 (for-next/selftests), thanks!
[1/4] kselftests/arm64: add a basic Pointer Authentication test https://git.kernel.org/arm64/c/e74e1d557285 [2/4] kselftests/arm64: add nop checks for PAuth tests https://git.kernel.org/arm64/c/766d95b1ed93 [3/4] kselftests/arm64: add PAuth test for whether exec() changes keys https://git.kernel.org/arm64/c/806a15b2545e [4/4] kselftests/arm64: add PAuth tests for single threaded consistency and differently initialized keys https://git.kernel.org/arm64/c/d21435e9670b
Cheers,
linux-kselftest-mirror@lists.linaro.org
-
Boyan Karatotev -
Will Deacon