Le 13/10/2021 à 09:16, Kees Cook a écrit :
On Mon, Oct 11, 2021 at 05:25:37PM +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.leroy@xxxxxxxxxx> --- drivers/misc/lkdtm/perms.c | 45 +++++++++++++++++++++++++++++++------- 1 file changed, 37 insertions(+), 8 deletions(-) diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c index da16564e1ecd..1d03cd44c21d 100644 --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -44,19 +44,42 @@ static noinline void do_overwritten(void) return; }+static void *setup_function_descriptor(funct_descr_t *fdesc, void *dst)+{ + int err; + + if (!__is_defined(HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR)) + return dst; + + err = copy_from_kernel_nofault(fdesc, do_nothing, sizeof(*fdesc)); + if (err < 0) + return ERR_PTR(err); + + fdesc->addr = (unsigned long)dst; + barrier(); + + return fdesc; +} + static noinline void execute_location(void *dst, bool write) { - void (*func)(void) = dst; + void (*func)(void); + funct_descr_t fdesc; + void *do_nothing_text = dereference_symbol_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); + func = setup_function_descriptor(&fdesc, dst); + if (IS_ERR(func)) + return;I think this error case should complain with some details. :) Maybe: pr_err("FAIL: could not build function descriptor for %px\n", dst);
Ok, I was going to add that in v2, but after one more thought I realise that there's no need to use copy_from_kernel_nofault() here, we are copying a static object into our stack, so a memcpy() will be good enough.
+ + pr_info("attempting bad execution at %px\n", dst);And then leave this pr_info() as it was, before the setup_function_descriptor() call.func(); pr_err("FAIL: func returned\n"); } @@ -66,16 +89,22 @@ static void execute_user_location(void *dst) int copied;/* Intentionally crossing kernel/user memory boundary. */- void (*func)(void) = dst; + void (*func)(void); + funct_descr_t fdesc; + void *do_nothing_text = dereference_symbol_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); + func = setup_function_descriptor(&fdesc, dst); + if (IS_ERR(func)) + return; + + pr_info("attempting bad execution at %px\n", dst);Same here.func(); pr_err("FAIL: func returned\n"); } -- 2.31.1
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