Commit 72a86433 authored by Christophe Leroy's avatar Christophe Leroy Committed by Michael Ellerman
Browse files

lkdtm: Fix execute_[user]_location() 



execute_location() and execute_user_location() intent
to copy do_nothing() text and execute it at a new location.
However, at the time being it doesn't copy do_nothing() function
but do_nothing() function descriptor which still points to the
original text. So at the end it still executes do_nothing() at
its original location allthough using a copied function descriptor.

So, fix that by really copying do_nothing() text and build a new
function descriptor by copying do_nothing() function descriptor and
updating the target address with the new location.

Also fix the displayed addresses by dereferencing do_nothing()
function descriptor.

Signed-off-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/4055839683d8d643cd99be121f4767c7c611b970.1644928018.git.christophe.leroy@csgroup.eu
parent b6491339

drivers/misc/lkdtm/perms.c

+28 −9
Original line number Diff line number Diff line
@@ -44,19 +44,34 @@ static noinline void do_overwritten(void) 
	return;

}



static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)

{

	if (!have_function_descriptors())

		return dst;



	memcpy(fdesc, do_nothing, sizeof(*fdesc));

	fdesc->addr = (unsigned long)dst;

	barrier();



	return fdesc;

}



static noinline void execute_location(void *dst, bool write)

{

	void (*func)(void) = dst;

	void (*func)(void);

	func_desc_t fdesc;

	void *do_nothing_text = dereference_function_descriptor(do_nothing);



	pr_info("attempting ok execution at %px\n", do_nothing);

	pr_info("attempting ok execution at %px\n", do_nothing_text);

	do_nothing();



	if (write == CODE_WRITE) {

		memcpy(dst, do_nothing, EXEC_SIZE);

		memcpy(dst, do_nothing_text, EXEC_SIZE);

		flush_icache_range((unsigned long)dst,

				   (unsigned long)dst + EXEC_SIZE);

	}

	pr_info("attempting bad execution at %px\n", func);

	pr_info("attempting bad execution at %px\n", dst);

	func = setup_function_descriptor(&fdesc, dst);

	func();

	pr_err("FAIL: func returned\n");

}
@@ -66,16 +81,19 @@ static void execute_user_location(void *dst) 
	int copied;



	/* Intentionally crossing kernel/user memory boundary. */

	void (*func)(void) = dst;

	void (*func)(void);

	func_desc_t fdesc;

	void *do_nothing_text = dereference_function_descriptor(do_nothing);



	pr_info("attempting ok execution at %px\n", do_nothing);

	pr_info("attempting ok execution at %px\n", do_nothing_text);

	do_nothing();



	copied = access_process_vm(current, (unsigned long)dst, do_nothing,

	copied = access_process_vm(current, (unsigned long)dst, do_nothing_text,

				   EXEC_SIZE, FOLL_WRITE);

	if (copied < EXEC_SIZE)

		return;

	pr_info("attempting bad execution at %px\n", func);

	pr_info("attempting bad execution at %px\n", dst);

	func = setup_function_descriptor(&fdesc, dst);

	func();

	pr_err("FAIL: func returned\n");

}
@@ -153,7 +171,8 @@ void lkdtm_EXEC_VMALLOC(void) 


void lkdtm_EXEC_RODATA(void)

{

	execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);

	execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing),

			 CODE_AS_IS);

}



void lkdtm_EXEC_USERSPACE(void)