[PATCH v1 10/10] lkdtm: Fix execute_[user]_location()

Christophe Leroy
2021-10-11T15:25:37Z

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: Christophe Leroy <christophe.leroy@csgroup.eu>
---
drivers/misc/lkdtm/perms.c | 45 +++++++++++++++++++++++++++++++-------
1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index da16564e1ecd..1d03cd44c21d 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -44,19 +44,42 @@ static noinline void do_overwritten(void)
return;
}

+static void *setup_function_descriptor(funct_descr_t *fdesc, void *dst)
+{
+ int err;
+
+ if (!__is_defined(HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR))
+ return dst;
+
+ err = copy_from_kernel_nofault(fdesc, do_nothing, sizeof(*fdesc));
+ if (err < 0)
+ return ERR_PTR(err);
+
+ fdesc->addr = (unsigned long)dst;
+ barrier();
+
+ return fdesc;
+}
+
static noinline void execute_location(void *dst, bool write)
{
- void (*func)(void) = dst;
+ void (*func)(void);
+ funct_descr_t fdesc;
+ void *do_nothing_text = dereference_symbol_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);
+ func = setup_function_descriptor(&fdesc, dst);
+ if (IS_ERR(func))
+ return;
+
+ pr_info("attempting bad execution at %px\n", dst);
func();
pr_err("FAIL: func returned\n");
}
@@ -66,16 +89,22 @@ static void execute_user_location(void *dst)
int copied;

/* Intentionally crossing kernel/user memory boundary. */
- void (*func)(void) = dst;
+ void (*func)(void);
+ funct_descr_t fdesc;
+ void *do_nothing_text = dereference_symbol_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);
+ func = setup_function_descriptor(&fdesc, dst);
+ if (IS_ERR(func))
+ return;
+
+ pr_info("attempting bad execution at %px\n", dst);
func();
pr_err("FAIL: func returned\n");
}
--
2.31.1