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Message-ID: <20241122085521.270802-1-maciej.wieczor-retman@intel.com>
Date: Fri, 22 Nov 2024 09:55:20 +0100
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
To: 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>
Cc: kirill@...temov.name,
maciej.wieczor-retman@...el.com,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH v3] selftests/lam: Test get_user() LAM pointer handling
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;
+ }
+
+ munmap(p, 1);
+
+ ptr = mmap((void *)ptr_address, 1, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+
+ if (ptr == MAP_FAILED) {
+ perror("failed to map byte to pass into get_user");
+ return 1;
+ }
+
+ if (test->lam != 0) {
+ 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);
+ 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
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