[PATCH v6 0/3] selftests/lam: get_user additions and LAM enabled check

[PATCH v6 0/3] selftests/lam: get_user additions and LAM enabled check

[Maciej Wieczor-Retman]

Changes in v6:
- Move la57 check to using mmap().
- Merge kernel_has_lam() and cpu_has_lam() into lam_is_available() since
  the syscall (if CONFIG_ADDRESS_MASKING is set) and cpuid check
  provides the same information.

Recent change in how get_user() handles pointers [1] has a specific case
for LAM. It assigns a different bitmask that's later used to check
whether a pointer comes from userland in get_user().

While currently commented out (until LASS [2] is merged into the kernel)
it's worth making changes to the LAM selftest ahead of time.

Modify cpu_has_la57() so it provides current paging level information
instead of the cpuid one.

Add test case to LAM that utilizes a ioctl (FIOASYNC) syscall which uses
get_user() in its implementation. Execute the syscall with differently
tagged pointers to verify that valid user pointers are passing through
and invalid kernel/non-canonical pointers are not.

Also to avoid unhelpful test failures add a check in main() to skip
running tests if LAM was not compiled into the kernel.

Code was tested on a Sierra Forest Xeon machine that's LAM capable. The
test was ran without issues with both the LAM lines from [1] untouched
and commented out. The test was also ran without issues with LAM_SUP
both enabled and disabled.

4/5 level pagetables code paths were also successfully tested in Simics
on a 5-level capable machine.

[1] https://lore.kernel.org/all/20241024013214.129639-1-torvalds@linux-foundation.org/
[2] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/

Previous series entries:
[v1] https://lore.kernel.org/all/20241029141421.715686-1-maciej.wieczor-retman@intel.com/
[v2] https://lore.kernel.org/all/20241121090651.254054-1-maciej.wieczor-retman@intel.com/
[v3] https://lore.kernel.org/all/20241122085521.270802-1-maciej.wieczor-retman@intel.com/
[v4] https://lore.kernel.org/all/cover.1732627541.git.maciej.wieczor-retman@intel.com/
[v5] https://lore.kernel.org/all/cover.1732728879.git.maciej.wieczor-retman@intel.com/

Maciej Wieczor-Retman (3):
  selftests/lam: Move cpu_has_la57() to use cpuinfo flag
  selftests/lam: Skip test if LAM is disabled
  selftests/lam: Test get_user() LAM pointer handling

 tools/testing/selftests/x86/lam.c | 147 +++++++++++++++++++++++++++---
 1 file changed, 136 insertions(+), 11 deletions(-)

-- 
2.47.1

[PATCH v6 1/3] selftests/lam: Move cpu_has_la57() to use cpuinfo flag

[Maciej Wieczor-Retman]

In current form cpu_has_la57() reports platform's support for LA57
through reading the output of cpuid. A much more useful information is
whether 5-level paging is actually enabled on the running system.

Check whether 5-level paging is enabled by trying to map a page in the
high linear address space.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v6:
- Go back to using mmap() to check la57 status.

Changelog v5:
- Remove "cat" from system() call and use only "grep".

Changelog v4:
- Add this patch to the series.

 tools/testing/selftests/x86/lam.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 0ea4f6813930..1ce6cf322c3c 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -124,14 +124,18 @@ static inline int cpu_has_lam(void)
 	return (cpuinfo[0] & (1 << 26));
 }
 
-/* Check 5-level page table feature in CPUID.(EAX=07H, ECX=00H):ECX.[bit 16] */
-static inline int cpu_has_la57(void)
+static inline int la57_enabled(void)
 {
-	unsigned int cpuinfo[4];
+	int ret;
+	void *p;
+
+	p = mmap((void *)HIGH_ADDR, PAGE_SIZE, PROT_READ | PROT_WRITE,
+		 MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
 
-	__cpuid_count(0x7, 0, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
+	ret = p == MAP_FAILED ? 0 : 1;
 
-	return (cpuinfo[2] & (1 << 16));
+	munmap(p, PAGE_SIZE);
+	return ret;
 }
 
 /*
@@ -322,7 +326,7 @@ static int handle_mmap(struct testcases *test)
 		   flags, -1, 0);
 	if (ptr == MAP_FAILED) {
 		if (test->addr == HIGH_ADDR)
-			if (!cpu_has_la57())
+			if (!la57_enabled())
 				return 3; /* unsupport LA57 */
 		return 1;
 	}
-- 
2.47.1

[PATCH v6 2/3] selftests/lam: Skip test if LAM is disabled

[Maciej Wieczor-Retman]

Until LASS is merged into the kernel [1], LAM is left disabled in the
config file. Running the LAM selftest with disabled LAM only results in
unhelpful output.

Use one of LAM syscalls() to determine whether the kernel was compiled
with LAM support (CONFIG_ADDRESS_MASKING) or not. Skip running the tests
in the latter case.

Merge cpuid checking function with the one mentioned above to achieve a
single function that shows LAM's availability from both CPU and the
kernel.

[1] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v6:
- Merge cpuid and kernel_has_lam() functions into one
  lam_is_available().

Changelog v4:
- Add this patch to the series.

 tools/testing/selftests/x86/lam.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 1ce6cf322c3c..140011bc39c0 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -115,13 +115,28 @@ static void segv_handler(int sig)
 	siglongjmp(segv_env, 1);
 }
 
-static inline int cpu_has_lam(void)
+static inline int lam_is_available(void)
 {
 	unsigned int cpuinfo[4];
+	unsigned long bits = 0;
+	int ret;
 
 	__cpuid_count(0x7, 1, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
 
-	return (cpuinfo[0] & (1 << 26));
+	/* Check if cpu supports LAM */
+	if (!(cpuinfo[0] & (1 << 26))) {
+		ksft_print_msg("LAM is not supported!\n");
+		return 0;
+	}
+
+	/* Return 0 if CONFIG_ADDRESS_MASKING is not set */
+	ret = syscall(SYS_arch_prctl, ARCH_GET_MAX_TAG_BITS, &bits);
+	if (ret) {
+		ksft_print_msg("LAM is disabled in the kernel!\n");
+		return 0;
+	}
+
+	return 1;
 }
 
 static inline int la57_enabled(void)
@@ -1185,10 +1200,8 @@ int main(int argc, char **argv)
 
 	tests_cnt = 0;
 
-	if (!cpu_has_lam()) {
-		ksft_print_msg("Unsupported LAM feature!\n");
+	if (!lam_is_available())
 		return KSFT_SKIP;
-	}
 
 	while ((c = getopt(argc, argv, "ht:")) != -1) {
 		switch (c) {
-- 
2.47.1

[PATCH v6 3/3] selftests/lam: Test get_user() LAM pointer handling

[Maciej Wieczor-Retman]

Recent change in how get_user() handles pointers [1] has a specific case
for LAM. It assigns a different bitmask that's later used to check
whether a pointer comes from userland in get_user().

Add test case to LAM that utilizes a ioctl (FIOASYNC) syscall which uses
get_user() in its implementation. Execute the syscall with differently
tagged pointers to verify that valid user pointers are passing through
and invalid kernel/non-canonical pointers are not.

[1] https://lore.kernel.org/all/20241024013214.129639-1-torvalds@linux-foundation.org/

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v6:
- Update la57 checking function name.
- Fix typo and add comment to the ioctl() usage.

Changelog v4:
- Use the changed cpu_has_la57() instead of mmap() to figure out current
  paging level.
- Apply Kirill's other comments: Remove redundant always true check,
  close the ioctl file before exiting, change mapping size to PAGE_SIZE
  so it looks less odd.
- Turn this patch into a series and move some text to the cover letter.

Changelog v3:
- mmap the pointer passed to get_user to high address if 5 level paging
  is enabled and to low address if 4 level paging is enabled.

Changelog v2:
- Use mmap with HIGH_ADDR to check if we're in 5 or 4 level pagetables.

 tools/testing/selftests/x86/lam.c | 108 ++++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 140011bc39c0..6e013dfac35e 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -4,6 +4,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/syscall.h>
+#include <sys/ioctl.h>
 #include <time.h>
 #include <signal.h>
 #include <setjmp.h>
@@ -43,7 +44,15 @@
 #define FUNC_INHERITE           0x20
 #define FUNC_PASID              0x40
 
+/* get_user() pointer test cases */
+#define GET_USER_USER           0
+#define GET_USER_KERNEL_TOP     1
+#define GET_USER_KERNEL_BOT     2
+#define GET_USER_KERNEL         3
+
 #define TEST_MASK               0x7f
+#define L5_SIGN_EXT_MASK        (0xFFUL << 56)
+#define L4_SIGN_EXT_MASK        (0x1FFFFUL << 47)
 
 #define LOW_ADDR                (0x1UL << 30)
 #define HIGH_ADDR               (0x3UL << 48)
@@ -389,6 +398,78 @@ static int handle_syscall(struct testcases *test)
 	return ret;
 }
 
+static int get_user_syscall(struct testcases *test)
+{
+	uint64_t ptr_address, bitmask;
+	int fd, ret = 0;
+	void *ptr;
+
+	if (la57_enabled()) {
+		bitmask = L5_SIGN_EXT_MASK;
+		ptr_address = HIGH_ADDR;
+	} else {
+		bitmask = L4_SIGN_EXT_MASK;
+		ptr_address = LOW_ADDR;
+	}
+
+	ptr = mmap((void *)ptr_address, PAGE_SIZE, PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+
+	if (ptr == MAP_FAILED) {
+		perror("failed to map byte to pass into get_user");
+		return 1;
+	}
+
+	if (set_lam(test->lam) != 0) {
+		ret = 2;
+		goto error;
+	}
+
+	fd = memfd_create("lam_ioctl", 0);
+	if (fd == -1) {
+		munmap(ptr, PAGE_SIZE);
+		exit(EXIT_FAILURE);
+	}
+
+	switch (test->later) {
+	case GET_USER_USER:
+		/* Control group - properly tagged user pointer */
+		ptr = (void *)set_metadata((uint64_t)ptr, test->lam);
+		break;
+	case GET_USER_KERNEL_TOP:
+		/* Kernel address with top bit cleared */
+		bitmask &= (bitmask >> 1);
+		ptr = (void *)((uint64_t)ptr | bitmask);
+		break;
+	case GET_USER_KERNEL_BOT:
+		/* Kernel address with bottom sign-extension bit cleared */
+		bitmask &= (bitmask << 1);
+		ptr = (void *)((uint64_t)ptr | bitmask);
+		break;
+	case GET_USER_KERNEL:
+		/* Try to pass a kernel address */
+		ptr = (void *)((uint64_t)ptr | bitmask);
+		break;
+	default:
+		printf("Invalid test case value passed!\n");
+		break;
+	}
+
+	/*
+	 * Use FIOASYNC ioctl because it utilizes get_user() internally and is
+	 * very non-invasive to the system. Pass differently tagged pointers to
+	 * get_user() in order to verify that valid user pointers are going
+	 * through and invalid kernel/non-canonical pointers are not.
+	 */
+	if (ioctl(fd, FIOASYNC, ptr) != 0)
+		ret = 1;
+
+	close(fd);
+error:
+	munmap(ptr, PAGE_SIZE);
+	return ret;
+}
+
 int sys_uring_setup(unsigned int entries, struct io_uring_params *p)
 {
 	return (int)syscall(__NR_io_uring_setup, entries, p);
@@ -902,6 +983,33 @@ static struct testcases syscall_cases[] = {
 		.test_func = handle_syscall,
 		.msg = "SYSCALL:[Negative] Disable LAM. Dereferencing pointer with metadata.\n",
 	},
+	{
+		.later = GET_USER_USER,
+		.lam = LAM_U57_BITS,
+		.test_func = get_user_syscall,
+		.msg = "GET_USER: get_user() and pass a properly tagged user pointer.\n",
+	},
+	{
+		.later = GET_USER_KERNEL_TOP,
+		.expected = 1,
+		.lam = LAM_U57_BITS,
+		.test_func = get_user_syscall,
+		.msg = "GET_USER:[Negative] get_user() with a kernel pointer and the top bit cleared.\n",
+	},
+	{
+		.later = GET_USER_KERNEL_BOT,
+		.expected = 1,
+		.lam = LAM_U57_BITS,
+		.test_func = get_user_syscall,
+		.msg = "GET_USER:[Negative] get_user() with a kernel pointer and the bottom sign-extension bit cleared.\n",
+	},
+	{
+		.later = GET_USER_KERNEL,
+		.expected = 1,
+		.lam = LAM_U57_BITS,
+		.test_func = get_user_syscall,
+		.msg = "GET_USER:[Negative] get_user() and pass a kernel pointer.\n",
+	},
 };
 
 static struct testcases mmap_cases[] = {
-- 
2.47.1