[PATCH v4 12/13] lkdtm: Fix execute_[user]_location()

[Christophe Leroy]

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.le...@csgroup.eu>
Acked-by: Kees Cook <keesc...@chromium.org>
---
 drivers/misc/lkdtm/perms.c | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 035fcca441f0..1cf24c4a79e9 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -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)
-- 
2.34.1