On 9/22/20 4:11 PM, Catalin Marinas wrote:
On Tue, Sep 01, 2020 at 02:57:19PM +0530, Amit Daniel Kachhap wrote:
Add a testcase to check that user address with valid/invalid
mte tag works in kernel mode. This test verifies the kernel API's
__arch_copy_from_user/__arch_copy_to_user works by considering
if the user pointer has valid/invalid allocation tags.
In MTE sync mode a SIGSEV fault is generated if a user memory
with invalid tag is accessed in kernel. In async mode no such
fault occurs.
We don't generate a SIGSEGV for faults in the uaccess routines. The
kernel simply returns less copied bytes than what was requested or -1
and setting errno.
ok. I will update in the next iteration.
BTW, Qemu has a bug and it reports the wrong exception class (lower
DABT) for a tag check fault while in the uaccess routines, leading to
kernel panic (bad mode in synchronous abort handler).
Yes I am also seeing this.
+static int check_usermem_access_fault(int mem_type, int mode, int mapping)
+{
+ int fd, ret, i, err;
+ char val = 'A';
+ size_t len, read_len;
+ void *ptr, *ptr_next;
+ bool fault;
+
+ len = 2 * page_sz;
+ err = KSFT_FAIL;
+ /*
+ * Accessing user memory in kernel with invalid tag should fault in sync
+ * mode but may not fault in async mode as per the implemented MTE
+ * support in Arm64 kernel.
+ */
+ if (mode == MTE_ASYNC_ERR)
+ fault = false;
+ else
+ fault = true;
+ mte_switch_mode(mode, MTE_ALLOW_NON_ZERO_TAG);
+ fd = create_temp_file();
+ if (fd == -1)
+ return KSFT_FAIL;
+ for (i = 0; i < len; i++)
+ write(fd, &val, sizeof(val));
+ lseek(fd, 0, 0);
+ ptr = mte_allocate_memory(len, mem_type, mapping, true);
+ if (check_allocated_memory(ptr, len, mem_type, true) != KSFT_PASS) {
+ close(fd);
+ return KSFT_FAIL;
+ }
+ mte_initialize_current_context(mode, (uintptr_t)ptr, len);
+ /* Copy from file into buffer with valid tag */
+ read_len = read(fd, ptr, len);
+ ret = errno;
My reading of the man page is that errno is set only if read() returns
-1.
Yes. The checks should be optimized here.
+ mte_wait_after_trig();
+ if ((cur_mte_cxt.fault_valid == true) || ret == EFAULT || read_len < len)
+ goto usermem_acc_err;
+ /* Verify same pattern is read */
+ for (i = 0; i < len; i++)
+ if (*(char *)(ptr + i) != val)
+ break;
+ if (i < len)
+ goto usermem_acc_err;
+
+ /* Tag the next half of memory with different value */
+ ptr_next = (void *)((unsigned long)ptr + page_sz);
+ ptr_next = mte_insert_tags(ptr_next, page_sz);
+ if (!ptr_next)
+ goto usermem_acc_err;
+ lseek(fd, 0, 0);
+ /* Copy from file into buffer with invalid tag */
+ read_len = read(fd, ptr, len);
+ ret = errno;
+ mte_wait_after_trig();
+ if ((fault == true) &&
Nitpick: just use "if (fault &&), it's a bool already.
ok.
+ (cur_mte_cxt.fault_valid == true || ret == EFAULT || read_len < len)) {
+ err = KSFT_PASS;
+ } else if ((fault == false) &&
+ (cur_mte_cxt.fault_valid == false && read_len == len)) {
Same here, !fault, !cur_mte_cxt.fault_valid.
ok.
