On Sun, Oct 17, 2021 at 02:38:24PM +0200, Christophe Leroy wrote:
> 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>
This looks good. I might rename variables in the future (e.g. to avoid
the churn from adding _text) but also, that does help keep it clear. :)
Acked-by: Kees Cook <keesc...@chromium.org>
-Kees
> ---
> 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)
> --
> 2.31.1
>
--
Kees Cook
