Re: [PATCH v4 07/10] selftests: riscv: Add a pointer masking test

[Charlie Jenkins <charlie@rivosinc.com>]

On Wed, Aug 28, 2024 at 06:01:29PM -0700, Samuel Holland wrote:
> This test covers the behavior of the PR_SET_TAGGED_ADDR_CTRL and
> PR_GET_TAGGED_ADDR_CTRL prctl() operations, their effects on the
> userspace ABI, and their effects on the system call ABI.
> 
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>

> ---
> 
> (no changes since v2)
> 
> Changes in v2:
>  - Rename "tags" directory to "pm" to avoid .gitignore rules
>  - Add .gitignore file to ignore the compiled selftest binary
>  - Write to a pipe to force dereferencing the user pointer
>  - Handle SIGSEGV in the child process to reduce dmesg noise
> 
>  tools/testing/selftests/riscv/Makefile        |   2 +-
>  tools/testing/selftests/riscv/pm/.gitignore   |   1 +
>  tools/testing/selftests/riscv/pm/Makefile     |  10 +
>  .../selftests/riscv/pm/pointer_masking.c      | 330 ++++++++++++++++++
>  4 files changed, 342 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/riscv/pm/.gitignore
>  create mode 100644 tools/testing/selftests/riscv/pm/Makefile
>  create mode 100644 tools/testing/selftests/riscv/pm/pointer_masking.c
> 
> diff --git a/tools/testing/selftests/riscv/Makefile b/tools/testing/selftests/riscv/Makefile
> index 7ce03d832b64..2ee1d1548c5f 100644
> --- a/tools/testing/selftests/riscv/Makefile
> +++ b/tools/testing/selftests/riscv/Makefile
> @@ -5,7 +5,7 @@
>  ARCH ?= $(shell uname -m 2>/dev/null || echo not)
>  
>  ifneq (,$(filter $(ARCH),riscv))
> -RISCV_SUBTARGETS ?= hwprobe vector mm sigreturn
> +RISCV_SUBTARGETS ?= hwprobe mm pm sigreturn vector
>  else
>  RISCV_SUBTARGETS :=
>  endif
> diff --git a/tools/testing/selftests/riscv/pm/.gitignore b/tools/testing/selftests/riscv/pm/.gitignore
> new file mode 100644
> index 000000000000..b38358f91c4d
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/pm/.gitignore
> @@ -0,0 +1 @@
> +pointer_masking
> diff --git a/tools/testing/selftests/riscv/pm/Makefile b/tools/testing/selftests/riscv/pm/Makefile
> new file mode 100644
> index 000000000000..ed82ff9c664e
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/pm/Makefile
> @@ -0,0 +1,10 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +CFLAGS += -I$(top_srcdir)/tools/include
> +
> +TEST_GEN_PROGS := pointer_masking
> +
> +include ../../lib.mk
> +
> +$(OUTPUT)/pointer_masking: pointer_masking.c
> +	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
> diff --git a/tools/testing/selftests/riscv/pm/pointer_masking.c b/tools/testing/selftests/riscv/pm/pointer_masking.c
> new file mode 100644
> index 000000000000..0fe80f963ace
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/pm/pointer_masking.c
> @@ -0,0 +1,330 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <setjmp.h>
> +#include <signal.h>
> +#include <stdbool.h>
> +#include <sys/prctl.h>
> +#include <sys/wait.h>
> +#include <unistd.h>
> +
> +#include "../../kselftest.h"
> +
> +#ifndef PR_PMLEN_SHIFT
> +#define PR_PMLEN_SHIFT			24
> +#endif
> +#ifndef PR_PMLEN_MASK
> +#define PR_PMLEN_MASK			(0x7fUL << PR_PMLEN_SHIFT)
> +#endif
> +
> +static int dev_zero;
> +
> +static int pipefd[2];
> +
> +static sigjmp_buf jmpbuf;
> +
> +static void sigsegv_handler(int sig)
> +{
> +	siglongjmp(jmpbuf, 1);
> +}
> +
> +static int min_pmlen;
> +static int max_pmlen;
> +
> +static inline bool valid_pmlen(int pmlen)
> +{
> +	return pmlen == 0 || pmlen == 7 || pmlen == 16;
> +}
> +
> +static void test_pmlen(void)
> +{
> +	ksft_print_msg("Testing available PMLEN values\n");
> +
> +	for (int request = 0; request <= 16; request++) {
> +		int pmlen, ret;
> +
> +		ret = prctl(PR_SET_TAGGED_ADDR_CTRL, request << PR_PMLEN_SHIFT, 0, 0, 0);
> +		if (ret)
> +			goto pr_set_error;
> +
> +		ret = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
> +		ksft_test_result(ret >= 0, "PMLEN=%d PR_GET_TAGGED_ADDR_CTRL\n", request);
> +		if (ret < 0)
> +			goto pr_get_error;
> +
> +		pmlen = (ret & PR_PMLEN_MASK) >> PR_PMLEN_SHIFT;
> +		ksft_test_result(pmlen >= request, "PMLEN=%d constraint\n", request);
> +		ksft_test_result(valid_pmlen(pmlen), "PMLEN=%d validity\n", request);
> +
> +		if (min_pmlen == 0)
> +			min_pmlen = pmlen;
> +		if (max_pmlen < pmlen)
> +			max_pmlen = pmlen;
> +
> +		continue;
> +
> +pr_set_error:
> +		ksft_test_result_skip("PMLEN=%d PR_GET_TAGGED_ADDR_CTRL\n", request);
> +pr_get_error:
> +		ksft_test_result_skip("PMLEN=%d constraint\n", request);
> +		ksft_test_result_skip("PMLEN=%d validity\n", request);
> +	}
> +
> +	if (max_pmlen == 0)
> +		ksft_exit_fail_msg("Failed to enable pointer masking\n");
> +}
> +
> +static int set_tagged_addr_ctrl(int pmlen, bool tagged_addr_abi)
> +{
> +	int arg, ret;
> +
> +	arg = pmlen << PR_PMLEN_SHIFT | tagged_addr_abi;
> +	ret = prctl(PR_SET_TAGGED_ADDR_CTRL, arg, 0, 0, 0);
> +	if (!ret) {
> +		ret = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
> +		if (ret == arg)
> +			return 0;
> +	}
> +
> +	return ret < 0 ? -errno : -ENODATA;
> +}
> +
> +static void test_dereference_pmlen(int pmlen)
> +{
> +	static volatile int i;
> +	volatile int *p;
> +	int ret;
> +
> +	ret = set_tagged_addr_ctrl(pmlen, false);
> +	if (ret)
> +		return ksft_test_result_error("PMLEN=%d setup (%d)\n", pmlen, ret);
> +
> +	i = pmlen;
> +
> +	if (pmlen) {
> +		p = (volatile int *)((uintptr_t)&i | 1UL << __riscv_xlen - pmlen);
> +
> +		/* These dereferences should succeed. */
> +		if (sigsetjmp(jmpbuf, 1))
> +			return ksft_test_result_fail("PMLEN=%d valid tag\n", pmlen);
> +		if (*p != pmlen)
> +			return ksft_test_result_fail("PMLEN=%d bad value\n", pmlen);
> +		*p++;
> +	}
> +
> +	p = (volatile int *)((uintptr_t)&i | 1UL << __riscv_xlen - pmlen - 1);
> +
> +	/* These dereferences should raise SIGSEGV. */
> +	if (sigsetjmp(jmpbuf, 1))
> +		return ksft_test_result_pass("PMLEN=%d dereference\n", pmlen);
> +	*p++;
> +	ksft_test_result_fail("PMLEN=%d invalid tag\n", pmlen);
> +}
> +
> +static void test_dereference(void)
> +{
> +	ksft_print_msg("Testing userspace pointer dereference\n");
> +
> +	signal(SIGSEGV, sigsegv_handler);
> +
> +	test_dereference_pmlen(0);
> +	test_dereference_pmlen(min_pmlen);
> +	test_dereference_pmlen(max_pmlen);
> +
> +	signal(SIGSEGV, SIG_DFL);
> +}
> +
> +static void execve_child_sigsegv_handler(int sig)
> +{
> +	exit(42);
> +}
> +
> +static int execve_child(void)
> +{
> +	static volatile int i;
> +	volatile int *p = (volatile int *)((uintptr_t)&i | 1UL << __riscv_xlen - 7);
> +
> +	signal(SIGSEGV, execve_child_sigsegv_handler);
> +
> +	/* This dereference should raise SIGSEGV. */
> +	return *p;
> +}
> +
> +static void test_fork_exec(void)
> +{
> +	int ret, status;
> +
> +	ksft_print_msg("Testing fork/exec behavior\n");
> +
> +	ret = set_tagged_addr_ctrl(min_pmlen, false);
> +	if (ret)
> +		return ksft_test_result_error("setup (%d)\n", ret);
> +
> +	if (fork()) {
> +		wait(&status);
> +		ksft_test_result(WIFEXITED(status) && WEXITSTATUS(status) == 42,
> +				 "dereference after fork\n");
> +	} else {
> +		static volatile int i = 42;
> +		volatile int *p = (volatile int *)((uintptr_t)&i | 1UL << __riscv_xlen - min_pmlen);
> +
> +		/* This dereference should succeed. */
> +		exit(*p);
> +	}
> +
> +	if (fork()) {
> +		wait(&status);
> +		ksft_test_result(WIFEXITED(status) && WEXITSTATUS(status) == 42,
> +				 "dereference after fork+exec\n");
> +	} else {
> +		/* Will call execve_child(). */
> +		execve("/proc/self/exe", (char *const []) { "", NULL }, NULL);
> +	}
> +}
> +
> +static void test_tagged_addr_abi_sysctl(void)
> +{
> +	char value;
> +	int fd;
> +
> +	ksft_print_msg("Testing tagged address ABI sysctl\n");
> +
> +	fd = open("/proc/sys/abi/tagged_addr_disabled", O_WRONLY);
> +	if (fd < 0) {
> +		ksft_test_result_skip("failed to open sysctl file\n");
> +		ksft_test_result_skip("failed to open sysctl file\n");
> +		return;
> +	}
> +
> +	value = '1';
> +	pwrite(fd, &value, 1, 0);
> +	ksft_test_result(set_tagged_addr_ctrl(min_pmlen, true) == -EINVAL,
> +			 "sysctl disabled\n");
> +
> +	value = '0';
> +	pwrite(fd, &value, 1, 0);
> +	ksft_test_result(set_tagged_addr_ctrl(min_pmlen, true) == 0,
> +			 "sysctl enabled\n");
> +
> +	set_tagged_addr_ctrl(0, false);
> +
> +	close(fd);
> +}
> +
> +static void test_tagged_addr_abi_pmlen(int pmlen)
> +{
> +	int i, *p, ret;
> +
> +	i = ~pmlen;
> +
> +	if (pmlen) {
> +		p = (int *)((uintptr_t)&i | 1UL << __riscv_xlen - pmlen);

I am trying to put something together with
https://lore.kernel.org/linux-mm/20240905-patches-below_hint_mmap-v3-2-3cd5564efbbb@rivosinc.com/T/
to ensure that the upper addresses aren't allocated. This is only
relevant on sv57 and PMLEN=16 hardware where addresses could overlap.

> +
> +		ret = set_tagged_addr_ctrl(pmlen, false);
> +		if (ret)
> +			return ksft_test_result_error("PMLEN=%d ABI disabled setup (%d)\n",
> +						      pmlen, ret);
> +
> +		ret = write(pipefd[1], p, sizeof(*p));
> +		if (ret >= 0 || errno != EFAULT)
> +			return ksft_test_result_fail("PMLEN=%d ABI disabled write\n", pmlen);
> +
> +		ret = read(dev_zero, p, sizeof(*p));
> +		if (ret >= 0 || errno != EFAULT)
> +			return ksft_test_result_fail("PMLEN=%d ABI disabled read\n", pmlen);
> +
> +		if (i != ~pmlen)
> +			return ksft_test_result_fail("PMLEN=%d ABI disabled value\n", pmlen);
> +
> +		ret = set_tagged_addr_ctrl(pmlen, true);
> +		if (ret)
> +			return ksft_test_result_error("PMLEN=%d ABI enabled setup (%d)\n",
> +						      pmlen, ret);
> +
> +		ret = write(pipefd[1], p, sizeof(*p));
> +		if (ret != sizeof(*p))
> +			return ksft_test_result_fail("PMLEN=%d ABI enabled write\n", pmlen);
> +
> +		ret = read(dev_zero, p, sizeof(*p));
> +		if (ret != sizeof(*p))
> +			return ksft_test_result_fail("PMLEN=%d ABI enabled read\n", pmlen);
> +
> +		if (i)
> +			return ksft_test_result_fail("PMLEN=%d ABI enabled value\n", pmlen);
> +
> +		i = ~pmlen;
> +	} else {
> +		/* The tagged address ABI cannot be enabled when PMLEN == 0. */
> +		ret = set_tagged_addr_ctrl(pmlen, true);
> +		if (ret != -EINVAL)
> +			return ksft_test_result_error("PMLEN=%d ABI setup (%d)\n",
> +						      pmlen, ret);
> +	}
> +
> +	p = (int *)((uintptr_t)&i | 1UL << __riscv_xlen - pmlen - 1);
> +
> +	ret = write(pipefd[1], p, sizeof(*p));
> +	if (ret >= 0 || errno != EFAULT)
> +		return ksft_test_result_fail("PMLEN=%d invalid tag write (%d)\n", pmlen, errno);
> +
> +	ret = read(dev_zero, p, sizeof(*p));
> +	if (ret >= 0 || errno != EFAULT)
> +		return ksft_test_result_fail("PMLEN=%d invalid tag read\n", pmlen);
> +
> +	if (i != ~pmlen)
> +		return ksft_test_result_fail("PMLEN=%d invalid tag value\n", pmlen);
> +
> +	ksft_test_result_pass("PMLEN=%d tagged address ABI\n", pmlen);
> +}
> +
> +static void test_tagged_addr_abi(void)
> +{
> +	ksft_print_msg("Testing tagged address ABI\n");
> +
> +	test_tagged_addr_abi_pmlen(0);
> +	test_tagged_addr_abi_pmlen(min_pmlen);
> +	test_tagged_addr_abi_pmlen(max_pmlen);
> +}
> +
> +static struct test_info {
> +	unsigned int nr_tests;
> +	void (*test_fn)(void);
> +} tests[] = {
> +	{ .nr_tests = 17 * 3, test_pmlen },
> +	{ .nr_tests = 3, test_dereference },
> +	{ .nr_tests = 2, test_fork_exec },
> +	{ .nr_tests = 2, test_tagged_addr_abi_sysctl },
> +	{ .nr_tests = 3, test_tagged_addr_abi },
> +};
> +
> +int main(int argc, char **argv)
> +{
> +	unsigned int plan = 0;
> +	int ret;
> +
> +	/* Check if this is the child process after execve(). */
> +	if (!argv[0][0])
> +		return execve_child();
> +
> +	dev_zero = open("/dev/zero", O_RDWR);
> +	if (dev_zero < 0)
> +		return 1;
> +
> +	/* Write to a pipe so the kernel must dereference the buffer pointer. */
> +	ret = pipe(pipefd);
> +	if (ret)
> +		return 1;
> +
> +	ksft_print_header();
> +
> +	for (int i = 0; i < ARRAY_SIZE(tests); ++i)
> +		plan += tests[i].nr_tests;
> +
> +	ksft_set_plan(plan);
> +
> +	for (int i = 0; i < ARRAY_SIZE(tests); ++i)
> +		tests[i].test_fn();
> +
> +	ksft_finished();
> +}
> -- 
> 2.45.1
> 
> 
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