Le 19/04/2020 à 10:06, Christoph Hellwig a écrit :
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.
About the branch, I was expecting GCC to inline and eliminate the unused
branch.
