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Message-ID: <kabcughnduiak2ipmzujq5gmsqu4ugfwxpd23gbic2hcinirb4@r3quhedtuvms>
Date: Fri, 22 Nov 2024 11:13:44 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3] selftests/lam: Test get_user() LAM pointer handling
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-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@...el.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?
> +
> + 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
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