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@xxxxxxxxxxxxxxxxxxxx/ >> [2] https://lore.kernel.org/all/20240710160655.3402786-1-alexander.shishkin@xxxxxxxxxxxxxxx/ >> >> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx> >> --- >> 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 -- Kind regards Maciej Wieczór-Retman
