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Subjectuaccess.h: implement unsafe_copy_{to,from}_user()?
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Commit 5b24a7a2aa2040c8c50c3b71122901d01661ff78 introduced the 
unsafe_get_user and unsafe_put_user replacement functions for batched calls
to put_user and get_user. I'm trying to make the kernel smaller and reduce
stac/clac overhead on x86 by substituting the new functions for such
batched calls. But there's no corresponding unsafe_copy_to_user()
or unsafe_copy_from_user() functions to copy an arbitrary-sized buffer to
and from userspace without calling access_ok and __uaccess_begin/end.

I know that the matter of replacing these uaccess functions has been
discussed at length (see https://lkml.org/lkml/2017/5/13/134), so before I
started hacking away implementing new unsafe_copy_{to,from}_user functions,
I wanted to ask if a solution to this is already being worked on or if
there's some way of accomplishing this goal without new functions.

To illustrate, here's a batched function call (from fs/fat/dir.c):

if (put_user(0, d2->d_name) ||
put_user(0, &d2->d_reclen) ||
copy_to_user(d1->d_name, name, name_len) ||
// etc...
goto efault;

This should read:

if (!access_ok(VERIFY_WRITE, d1, 2*sizeof(*infop))
goto efault;
user_access_begin();
unsafe_put_user(0, d2->d_name, efault)
unsafe_put_user(0, &d2->d_reclen, efault)
unsafe_copy_to_user(d1->d_name, name, name_len, efault); // we don't have
// this function

// etc...
user_access_end();



Thanks.

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