On 2024-11-22 at 11:13:44 +0200, Kirill A. Shutemov wrote:
On Fri, Nov 22, 2024 at 09:55:20AM +0100, Maciej Wieczor-Retman wrote:
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-foundatio... [2] https://lore.kernel.org/all/20240710160655.3402786-1-alexander.shishkin@linu...
Signed-off-by: Maciej Wieczor-Retman maciej.wieczor-retman@intel.com
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 | 110 ++++++++++++++++++++++++++++++ 1 file changed, 110 insertions(+)
diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c index 0ea4f6813930..616a523c3262 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 +379,80 @@ static int handle_syscall(struct testcases *test) return ret; } +static int get_user_syscall(struct testcases *test) +{
- uint64_t ptr_address, bitmask;
- void *p, *ptr;
- int ret = 0;
- int fd;
- p = mmap((void *)HIGH_ADDR, 1, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);- if (p == MAP_FAILED) {
bitmask = L4_SIGN_EXT_MASK;ptr_address = LOW_ADDR;- } else {
bitmask = L5_SIGN_EXT_MASK;ptr_address = HIGH_ADDR;- }
Hm. Why not use cpu_has_lam() for the paging check?
cpu_has_lam() seems to return what the cpuid reports about LAM being available on the system.
The problem I was trying to solve here was to determine what pagetable level is used currently so I can setup the bitmask to create fake kernel pointers below. Can cpu_has_lam() achieve that? I didn't see any correlation between the cpuid and active paging mode.
- munmap(p, 1);
- ptr = mmap((void *)ptr_address, 1, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);Mapping sizer of 1 byte looks odd. It is not wrong, but looks strange. Maybe use PAGE_SIZE instead?
Okay, I'll try that.
- if (ptr == MAP_FAILED) {
perror("failed to map byte to pass into get_user");return 1;- }
- if (test->lam != 0) {
It is always true, right?
Right, I forgot to remove it.
if (set_lam(test->lam) != 0) {ret = 2;goto error;}- }
- fd = memfd_create("lam_ioctl", 0);
- if (fd == -1) {
munmap(ptr, 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;+error:
- munmap(ptr, 1);
close(fd);
Thanks :)
- 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 +966,33 @@ 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
-- Kiryl Shutsemau / Kirill A. Shutemov