Le 13/10/2021 à 09:39, Christophe Leroy a écrit :
Le 13/10/2021 à 09:23, Kees Cook a écrit :
On Mon, Oct 11, 2021 at 05:25:36PM +0200, Christophe Leroy wrote:
Behind a location, lkdtm_EXEC_RODATA() executes a real function,
not a copy of do_nothing().
So do it directly instead of using execute_location().
And fix displayed addresses by dereferencing the function descriptors.
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
drivers/misc/lkdtm/perms.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 442d60ed25ef..da16564e1ecd 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -153,7 +153,14 @@ void lkdtm_EXEC_VMALLOC(void)
void lkdtm_EXEC_RODATA(void)
{
- execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
+ pr_info("attempting ok execution at %px\n",
+ dereference_symbol_descriptor(do_nothing));
+ do_nothing();
+
+ pr_info("attempting bad execution at %px\n",
+ dereference_symbol_descriptor(lkdtm_rodata_do_nothing));
+ lkdtm_rodata_do_nothing();
+ pr_err("FAIL: func returned\n");
}
(In re-reading this more carefully, I see now why kallsyms.h is used
earlier: _function_ vs _symbol_ descriptor.)
In the next patch:
static noinline void execute_location(void *dst, bool write)
{
...
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");
}
What are the conditions for which dereference_symbol_descriptor works
but dereference _function_descriptor doesn't?
When LKDTM is built as a module I guess ?
To be more precise, dereference_symbol_descriptor() calls either
dereference_kernel_function_descriptor() or
dereference_module_function_descriptor()
Both functions call dereference_function_descriptor() after checking
that we want to dereference something that is in the OPD section.
If we call dereference_function_descriptor() directly instead of
dereference_symbol_descriptor() we skip the range verification and may
dereference something that is not a function descriptor.
Should we do that ?
Christophe
