On Sat, Apr 18, 2020 at 10:15:42AM +0200, Christophe Leroy wrote: > > > Le 14/04/2020 à 09:01, Christoph Hellwig a écrit : >> Currently copy_string_kernel is just a wrapper around copy_strings that >> simplifies the calling conventions and uses set_fs to allow passing a >> kernel pointer. But due to the fact the we only need to handle a single >> kernel argument pointer, the logic can be sigificantly simplified while >> getting rid of the set_fs. > > > Instead of duplicating almost identical code, can you write a function that > takes whether the source is from user or from kernel, then you just do > things like: > > if (from_user) > len = strnlen_user(str, MAX_ARG_STRLEN); > else > len = strnlen(str, MAX_ARG_STRLEN); > > > if (from_user) > copy_from_user(kaddr+offset, str, bytes_to_copy); > else > memcpy(kaddr+offset, str, bytes_to_copy); We'll need two different str variables then with and without __user annotations to keep type safety. And introduce a branch-y and unreadable mess in the exec fast path instead of adding a simple and well understood function for the kernel case that just deals with the much simpler case of just copying a single arg vector from a kernel address.
