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? > + > + 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? > + > + 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? > + 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); > + 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
