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Commit f90d1e0c authored by Alexander Popov's avatar Alexander Popov Committed by Kees Cook
Browse files

lkdtm: Add a test for STACKLEAK 



Introduce an lkdtm test for the STACKLEAK feature: check that the
current task stack is properly erased (filled with STACKLEAK_POISON).

Signed-off-by: default avatarAlexander Popov <alex.popov@linux.com>
Signed-off-by: default avatarTycho Andersen <tycho@tycho.ws>
Tested-by: default avatarLaura Abbott <labbott@redhat.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 10e9ae9f

drivers/misc/lkdtm/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -8,7 +8,9 @@ lkdtm-$(CONFIG_LKDTM) += perms.o 
lkdtm-$(CONFIG_LKDTM)		+= refcount.o

lkdtm-$(CONFIG_LKDTM)		+= rodata_objcopy.o

lkdtm-$(CONFIG_LKDTM)		+= usercopy.o

lkdtm-$(CONFIG_LKDTM)		+= stackleak.o



KASAN_SANITIZE_stackleak.o	:= n

KCOV_INSTRUMENT_rodata.o	:= n



OBJCOPYFLAGS :=

drivers/misc/lkdtm/core.c

+1 −0
Original line number Diff line number Diff line
@@ -183,6 +183,7 @@ static const struct crashtype crashtypes[] = { 
	CRASHTYPE(USERCOPY_STACK_FRAME_FROM),

	CRASHTYPE(USERCOPY_STACK_BEYOND),

	CRASHTYPE(USERCOPY_KERNEL),

	CRASHTYPE(STACKLEAK_ERASING),

};

drivers/misc/lkdtm/lkdtm.h

+3 −0
Original line number Diff line number Diff line
@@ -83,4 +83,7 @@ void lkdtm_USERCOPY_STACK_FRAME_FROM(void); 
void lkdtm_USERCOPY_STACK_BEYOND(void);

void lkdtm_USERCOPY_KERNEL(void);



/* lkdtm_stackleak.c */

void lkdtm_STACKLEAK_ERASING(void);



#endif

drivers/misc/lkdtm/stackleak.c

0 → 100644
+73 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/*

 * This code tests that the current task stack is properly erased (filled

 * with STACKLEAK_POISON).

 *

 * Authors:

 *   Alexander Popov <alex.popov@linux.com>

 *   Tycho Andersen <tycho@tycho.ws>

 */



#include "lkdtm.h"

#include <linux/stackleak.h>



void lkdtm_STACKLEAK_ERASING(void)

{

	unsigned long *sp, left, found, i;

	const unsigned long check_depth =

			STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);



	/*

	 * For the details about the alignment of the poison values, see

	 * the comment in stackleak_track_stack().

	 */

	sp = PTR_ALIGN(&i, sizeof(unsigned long));



	left = ((unsigned long)sp & (THREAD_SIZE - 1)) / sizeof(unsigned long);

	sp--;



	/*

	 * One 'long int' at the bottom of the thread stack is reserved

	 * and not poisoned.

	 */

	if (left > 1) {

		left--;

	} else {

		pr_err("FAIL: not enough stack space for the test\n");

		return;

	}



	pr_info("checking unused part of the thread stack (%lu bytes)...\n",

					left * sizeof(unsigned long));



	/*

	 * Search for 'check_depth' poison values in a row (just like

	 * stackleak_erase() does).

	 */

	for (i = 0, found = 0; i < left && found <= check_depth; i++) {

		if (*(sp - i) == STACKLEAK_POISON)

			found++;

		else

			found = 0;

	}



	if (found <= check_depth) {

		pr_err("FAIL: thread stack is not erased (checked %lu bytes)\n",

						i * sizeof(unsigned long));

		return;

	}



	pr_info("first %lu bytes are unpoisoned\n",

				(i - found) * sizeof(unsigned long));



	/* The rest of thread stack should be erased */

	for (; i < left; i++) {

		if (*(sp - i) != STACKLEAK_POISON) {

			pr_err("FAIL: thread stack is NOT properly erased\n");

			return;

		}

	}



	pr_info("OK: the rest of the thread stack is properly erased\n");

	return;

}