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.

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.

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/20240710160655.3402786-1-alexander.shishkin@linux.intel.com/

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v2:
- Use mmap with HIGH_ADDR to check if we're in 5 or 4 level pagetables.

 tools/testing/selftests/x86/lam.c | 89 +++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 0ea4f6813930..5818c075e1cd 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)
@@ -370,6 +379,59 @@ static int handle_syscall(struct testcases *test)
 	return ret;
 }
 
+static int get_user_syscall(struct testcases *test)
+{
+	int ptr_value = 0;
+	int ret = 0;
+	int fd;
+	void *p, *ptr = &ptr_value;
+
+	p = mmap((void *)HIGH_ADDR, 1, PROT_READ | PROT_WRITE,
+		 MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+
+	uint64_t bitmask = (p == MAP_FAILED) ? L4_SIGN_EXT_MASK :
+					       L5_SIGN_EXT_MASK;
+
+	munmap(p, 1);
+
+	if (test->lam != 0)
+		if (set_lam(test->lam) != 0)
+			return 2;
+
+	fd = memfd_create("lam_ioctl", 0);
+	if (fd == -1)
+		exit(EXIT_FAILURE);
+
+	switch (test->later) {
+	case GET_USER_USER:
+		/* Control group - properly tagger 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;
+	}
+
+	if (ioctl(fd, FIOASYNC, ptr) != 0)
+		ret = 1;
+
+	return ret;
+}
+
 int sys_uring_setup(unsigned int entries, struct io_uring_params *p)
 {
 	return (int)syscall(__NR_io_uring_setup, entries, p);
@@ -883,6 +945,33 @@ 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[] = {
-- 
2.46.2