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Commit 7cca071c authored by Kees Cook's avatar Kees Cook Committed by Ingo Molnar
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lkdtm: Verify that '__ro_after_init' works correctly 



The new __ro_after_init section should be writable before init, but
not after. Validate that it gets updated at init and can't be written
to afterwards.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Brown <david.brown@linaro.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Emese Revfy <re.emese@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathias Krause <minipli@googlemail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: PaX Team <pageexec@freemail.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-hardening@lists.openwall.com
Cc: linux-arch <linux-arch@vger.kernel.org>
Link: http://lkml.kernel.org/r/1455748879-21872-6-git-send-email-keescook@chromium.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent c74ba8b3

drivers/misc/lkdtm.c

+26 −3
Original line number Diff line number Diff line
@@ -103,6 +103,7 @@ enum ctype { 
	CT_EXEC_USERSPACE,

	CT_ACCESS_USERSPACE,

	CT_WRITE_RO,

	CT_WRITE_RO_AFTER_INIT,

	CT_WRITE_KERN,

};
@@ -140,6 +141,7 @@ static char* cp_type[] = { 
	"EXEC_USERSPACE",

	"ACCESS_USERSPACE",

	"WRITE_RO",

	"WRITE_RO_AFTER_INIT",

	"WRITE_KERN",

};
@@ -162,6 +164,7 @@ static DEFINE_SPINLOCK(lock_me_up); 
static u8 data_area[EXEC_SIZE];



static const unsigned long rodata = 0xAA55AA55;

static unsigned long ro_after_init __ro_after_init = 0x55AA5500;



module_param(recur_count, int, 0644);

MODULE_PARM_DESC(recur_count, " Recursion level for the stack overflow test");
@@ -503,11 +506,28 @@ static void lkdtm_do_action(enum ctype which) 
		break;

	}

	case CT_WRITE_RO: {

		unsigned long *ptr;

		/* Explicitly cast away "const" for the test. */

		unsigned long *ptr = (unsigned long *)&rodata;



		ptr = (unsigned long *)&rodata;

		pr_info("attempting bad rodata write at %p\n", ptr);

		*ptr ^= 0xabcd1234;



		pr_info("attempting bad write at %p\n", ptr);

		break;

	}

	case CT_WRITE_RO_AFTER_INIT: {

		unsigned long *ptr = &ro_after_init;



		/*

		 * Verify we were written to during init. Since an Oops

		 * is considered a "success", a failure is to just skip the

		 * real test.

		 */

		if ((*ptr & 0xAA) != 0xAA) {

			pr_info("%p was NOT written during init!?\n", ptr);

			break;

		}



		pr_info("attempting bad ro_after_init write at %p\n", ptr);

		*ptr ^= 0xabcd1234;



		break;
@@ -817,6 +837,9 @@ static int __init lkdtm_module_init(void) 
	int n_debugfs_entries = 1; /* Assume only the direct entry */

	int i;



	/* Make sure we can write to __ro_after_init values during __init */

	ro_after_init |= 0xAA;



	/* Register debugfs interface */

	lkdtm_debugfs_root = debugfs_create_dir("provoke-crash", NULL);

	if (!lkdtm_debugfs_root) {