lkdtm/usercopy: Expand size of "out of frame" object

BugLink: https://bugs.launchpad.net/bugs/1982968
[ Upstream commit f387e86d3a74407bdd9c5815820ac9d060962840 ]

To be sufficiently out of range for the usercopy test to see the lifetime
mismatch, expand the size of the "bad" buffer, which will let it be
beyond current_stack_pointer regardless of stack growth direction.
Paired with the recent addition of stack depth checking under
CONFIG_HARDENED_USERCOPY=y, this will correctly start tripping again.

Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Link: https://lore.kernel.org/lkml/762faf1b-0443-5ddf-4430-44a20cf2ec4d@collabora.com/
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index 9161ce7ed47a6ce56cf9229c2a7300e15f53d0bc..3fead5efe523abb09274df2c68c14f301a8d60cb 100644 (file)
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -30,12 +30,12 @@ static const unsigned char test_text[] = "This is a test.\n";
  */
 static noinline unsigned char *trick_compiler(unsigned char *stack)
 {
-       return stack + 0;
+       return stack + unconst;
 }
 
 static noinline unsigned char *do_usercopy_stack_callee(int value)
 {
-       unsigned char buf[32];
+       unsigned char buf[128];
        int i;
 
        /* Exercise stack to avoid everything living in registers. */
@@ -43,7 +43,12 @@ static noinline unsigned char *do_usercopy_stack_callee(int value)
                buf[i] = value & 0xff;
        }
 
-       return trick_compiler(buf);
+       /*
+        * Put the target buffer in the middle of stack allocation
+        * so that we don't step on future stack users regardless
+        * of stack growth direction.
+        */
+       return trick_compiler(&buf[(128/2)-32]);
 }
 
 static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
@@ -66,6 +71,12 @@ static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
                bad_stack -= sizeof(unsigned long);
        }
 
+#ifdef ARCH_HAS_CURRENT_STACK_POINTER
+       pr_info("stack     : %px\n", (void *)current_stack_pointer);
+#endif
+       pr_info("good_stack: %px-%px\n", good_stack, good_stack + sizeof(good_stack));
+       pr_info("bad_stack : %px-%px\n", bad_stack, bad_stack + sizeof(good_stack));
+
        user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
                            PROT_READ | PROT_WRITE | PROT_EXEC,
                            MAP_ANONYMOUS | MAP_PRIVATE, 0);