kallsyms: Utilize ksymbol table for unauthorized address access

Access the system symbols with root permission to test whether it's
possible to read and write the memory addresses of kernel-space
from user-space. This helps in identifying potential vulnerabilities
where user-space processes can inappropriately access kernel memory.

Suggested-by: Rafael Aquini <[email protected]>
Suggested-by: Cyril Hrubis <[email protected]>
Signed-off-by: Li Wang <[email protected]>
Reviewed-by: Cyril Hrubis <[email protected]>

runtest/mm

@@ -58,6 +58,8 @@ mmap10_2 mmap10 -s
 mmap10_3 mmap10 -a -s
 mmap10_4 mmap10 -a -s -i 60
 
+kallsyms kallsyms
+
 ksm01 ksm01
 ksm01_1 ksm01 -u 128
 ksm02 ksm02

testcases/kernel/security/kallsyms/.gitignore

@@ -0,0 +1 @@
+kallsyms

testcases/kernel/security/kallsyms/Makefile

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+top_srcdir		?= ../../../..
+
+include $(top_srcdir)/include/mk/testcases.mk
+include $(top_srcdir)/include/mk/generic_leaf_target.mk

testcases/kernel/security/kallsyms/kallsyms.c

@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2024 Red Hat, Inc.
+ */
+
+/*\
+ * [Description]
+ *
+ *  Utilize kernel's symbol table for unauthorized address access.
+ *
+ *  Access the system symbols with root permission to test whether it's
+ *  possible to read and write the memory addresses of kernel-space
+ *  from user-space. This helps in identifying potential vulnerabilities
+ *  where user-space processes can inappropriately access kernel memory.
+ *
+ * Steps:
+ *  1. Start a process that reads all symbols and their addresses from
+ *     '/proc/kallsyms' and stores them in a linked list.
+ *
+ *  2. Attempt to write to each kernel address found in the linked list.
+ *     The expectation is that each attempt will fail with a SIGSEGV
+ *     (segmentation fault), indicating that the user-space process
+ *     cannot write to kernel memory.
+ *
+ *  3. Handle each SIGSEGV using a signal handler that sets a flag and
+ *     long jumps out of the faulting context.
+ *
+ *  4. If any write operation does not result in a SIGSEGV, log this as
+ *     a potential security vulnerability.
+ *
+ *  5. Observe and log the behavior and any system responses to these
+ *     unauthorized access attempts.
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <unistd.h>
+#include <string.h>
+#include <setjmp.h>
+#include <signal.h>
+
+#include "tst_test.h"
+#include "tst_safe_stdio.h"
+
+struct kallsym {
+	unsigned long addr;
+	char type;
+	char name[128];
+};
+
+static struct kallsym *sym_table;
+static unsigned int nr_symbols;
+static sigjmp_buf jmpbuf;
+volatile sig_atomic_t segv_caught;
+
+static void segv_handler(int sig)
+{
+	if (sig == SIGSEGV)
+		segv_caught++;
+	else
+		tst_res(TFAIL, "Unexpected signal %s", strsignal(sig));
+
+	siglongjmp(jmpbuf, 1);
+}
+
+static unsigned int read_kallsyms(struct kallsym *table, unsigned int table_size)
+{
+	char *line = NULL;
+	size_t len = 0;
+	unsigned int nr_syms = 0;
+	FILE *stream = SAFE_FOPEN("/proc/kallsyms", "r");
+
+	while (getline(&line, &len, stream) != -1) {
+
+		if (table && nr_syms < table_size) {
+			sscanf(line, "%lx %c %s",
+					&table[nr_syms].addr,
+					&table[nr_syms].type,
+					table[nr_syms].name);
+		}
+
+		nr_syms++;
+	}
+
+	SAFE_FCLOSE(stream);
+
+	return nr_syms;
+}
+
+static void setup(void)
+{
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = segv_handler;
+	sigaction(SIGSEGV, &sa, NULL);
+
+	nr_symbols = read_kallsyms(NULL, 0);
+	sym_table = SAFE_CALLOC(nr_symbols, sizeof(*sym_table));
+	unsigned int read_symbols = read_kallsyms(sym_table, nr_symbols);
+
+	if (nr_symbols != read_symbols)
+		tst_res(TWARN, "/proc/kallsyms changed size!?");
+}
+
+static void access_ksymbols_address(struct kallsym *table)
+{
+	tst_res(TDEBUG, "Access kernel addr: 0x%lx (%c) (%s)",
+				table->addr, table->type, table->name);
+
+	if (sigsetjmp(jmpbuf, 1) == 0) {
+		*(volatile unsigned long *)table->addr = 0;
+
+		tst_res(TFAIL, "Successfully accessed kernel addr 0x%lx (%c) (%s)",
+				table->addr, table->type, table->name);
+	}
+}
+
+static void test_access_kernel_address(void)
+{
+	segv_caught = 0;
+
+	for (unsigned int i = 0; i < nr_symbols; i++)
+		access_ksymbols_address(&sym_table[i]);
+
+	if (segv_caught == (sig_atomic_t)nr_symbols)
+		tst_res(TPASS, "Caught %d SIGSEGV in access ksymbols addr", segv_caught);
+	else
+		tst_res(TFAIL, "Caught %d SIGSEGV but expected %d", segv_caught, nr_symbols);
+}
+
+static void cleanup(void)
+{
+	if (sym_table)
+		free(sym_table);
+}
+
+static struct tst_test test = {
+	.needs_root = 1,
+	.setup = setup,
+	.cleanup = cleanup,
+	.max_runtime = 60,
+	.test_all = test_access_kernel_address,
+};