kselftest/arm64: Check mte tagged user address in kernel

Add a testcase to check that user address with valid/invalid
mte tag works in kernel mode. This test verifies that 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, file memory read/write and other similar interfaces
fails if a user memory with invalid tag is accessed in kernel. In async
mode no such failure occurs.

Signed-off-by: Amit Daniel Kachhap <[e-mail]>
Tested-by: Catalin Marinas <[e-mail]>
Acked-by: Catalin Marinas <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Will Deacon <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

tools/testing/selftests/arm64/mte/.gitignore

···
 check_child_memory
 check_mmap_options
 check_ksm_options
+check_user_mem

tools/testing/selftests/arm64/mte/check_user_mem.c

···
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2020 ARM Limited
+
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <ucontext.h>
+#include <unistd.h>
+#include <sys/mman.h>
+
+#include "kselftest.h"
+#include "mte_common_util.h"
+#include "mte_def.h"
+
+static size_t page_sz;
+
+static int check_usermem_access_fault(int mem_type, int mode, int mapping)
+{
+	int fd, i, err;
+	char val = 'A';
+	size_t len, read_len;
+	void *ptr, *ptr_next;
+
+	err = KSFT_FAIL;
+	len = 2 * page_sz;
+	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);
+	mte_wait_after_trig();
+	if (cur_mte_cxt.fault_valid || 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_new_tag(ptr_next);
+	mte_set_tag_address_range(ptr_next, page_sz);
+
+	lseek(fd, 0, 0);
+	/* Copy from file into buffer with invalid tag */
+	read_len = read(fd, ptr, len);
+	mte_wait_after_trig();
+	/*
+	 * Accessing user memory in kernel with invalid tag should fail in sync
+	 * mode without fault but may not fail in async mode as per the
+	 * implemented MTE userspace support in Arm64 kernel.
+	 */
+	if (mode == MTE_SYNC_ERR &&
+	    !cur_mte_cxt.fault_valid && read_len < len) {
+		err = KSFT_PASS;
+	} else if (mode == MTE_ASYNC_ERR &&
+		   !cur_mte_cxt.fault_valid && read_len == len) {
+		err = KSFT_PASS;
+	}
+usermem_acc_err:
+	mte_free_memory((void *)ptr, len, mem_type, true);
+	close(fd);
+	return err;
+}
+
+int main(int argc, char *argv[])
+{
+	int err;
+
+	page_sz = getpagesize();
+	if (!page_sz) {
+		ksft_print_msg("ERR: Unable to get page size\n");
+		return KSFT_FAIL;
+	}
+	err = mte_default_setup();
+	if (err)
+		return err;
+	/* Register signal handlers */
+	mte_register_signal(SIGSEGV, mte_default_handler);
+
+	evaluate_test(check_usermem_access_fault(USE_MMAP, MTE_SYNC_ERR, MAP_PRIVATE),
+		"Check memory access from kernel in sync mode, private mapping and mmap memory\n");
+	evaluate_test(check_usermem_access_fault(USE_MMAP, MTE_SYNC_ERR, MAP_SHARED),
+		"Check memory access from kernel in sync mode, shared mapping and mmap memory\n");
+
+	evaluate_test(check_usermem_access_fault(USE_MMAP, MTE_ASYNC_ERR, MAP_PRIVATE),
+		"Check memory access from kernel in async mode, private mapping and mmap memory\n");
+	evaluate_test(check_usermem_access_fault(USE_MMAP, MTE_ASYNC_ERR, MAP_SHARED),
+		"Check memory access from kernel in async mode, shared mapping and mmap memory\n");
+
+	mte_restore_setup();
+	ksft_print_cnts();
+	return ksft_get_fail_cnt() == 0 ? KSFT_PASS : KSFT_FAIL;
+}

tools/testing/selftests/arm64/mte/mte_common_util.h

···
 
 /* Assembly MTE utility functions */
 void *mte_insert_random_tag(void *ptr);
+void *mte_insert_new_tag(void *ptr);
 void *mte_get_tag_address(void *ptr);
 void mte_set_tag_address_range(void *ptr, int range);
 void mte_clear_tag_address_range(void *ptr, int range);

tools/testing/selftests/arm64/mte/mte_helper.S

···
 ENDPROC(mte_insert_random_tag)
 
 /*
+ * mte_insert_new_tag: Insert new tag and different from the source tag if
+ *		       source pointer has it.
+ * Input:
+ *		x0 - source pointer with a tag/no-tag
+ * Return:
+ *		x0 - pointer with random tag
+ */
+ENTRY(mte_insert_new_tag)
+	gmi	x1, x0, xzr
+	irg	x0, x0, x1
+	ret
+ENDPROC(mte_insert_new_tag)
+
+/*
  * mte_get_tag_address: Get the tag from given address.
  * Input:
  *		x0 - source pointer