Le 13/10/2021 à 09:05, Kees Cook a écrit :
On Mon, Oct 11, 2021 at 05:25:35PM +0200, Christophe Leroy wrote:
WRITE_KERN is supposed to overwrite some kernel text, namely
do_overwritten() function.
But at the time being it overwrites do_overwritten() function
descriptor, not function text.
Fix it by dereferencing the function descriptor to obtain
function text pointer.
And make do_overwritten() noinline so that it is really
do_overwritten() which is called by lkdtm_WRITE_KERN().
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
drivers/misc/lkdtm/perms.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 60b3b2fe929d..442d60ed25ef 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -5,6 +5,7 @@
* even non-readable regions.
*/
#include "lkdtm.h"
+#include <linux/kallsyms.h>
Why not #include <asm/sections.h> instead here?
dereference_symbol_descriptor() is defined in linux/kallsyms.h
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mman.h>
@@ -37,7 +38,7 @@ static noinline void do_nothing(void)
}
/* Must immediately follow do_nothing for size calculuations to work out. */
-static void do_overwritten(void)
+static noinline void do_overwritten(void)
{
pr_info("do_overwritten wasn't overwritten!\n");
return;
@@ -113,8 +114,9 @@ void lkdtm_WRITE_KERN(void)
size_t size;
volatile unsigned char *ptr;
- size = (unsigned long)do_overwritten - (unsigned long)do_nothing;
- ptr = (unsigned char *)do_overwritten;
+ size = (unsigned long)dereference_symbol_descriptor(do_overwritten) -
+ (unsigned long)dereference_symbol_descriptor(do_nothing);
+ ptr = dereference_symbol_descriptor(do_overwritten);
But otherwise, yup, I expect there will be a bunch of things like this
to clean up in LKDTM. :| Sorry about that!
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
pr_info("attempting bad %zu byte write at %px\n", size, ptr);
memcpy((void *)ptr, (unsigned char *)do_nothing, size);
--
2.31.1
