From: Geert Uytterhoeven
Sent: 24 February 2022 08:59
...
+register unsigned long current_stack_pointer __asm__("sp");I don't know what HARDENED_USERCOPY does, so I don't know if you need "usp" (see rdusp()) or "sp"?
HARDENED_USERCOPY significantly slows down some systems calls (especially things like sendmsg()) by trying to run-time verify that the kernel buffer doesn't overrun a stack frame or kmalloc()ed buffer. I've got measurable improvements by either using __copy_to/from_user() (which skips the tests) or user_access_begin() and __get_user(). At the moment the code for reading a compat iovec[] is actually faster than that for a native one! David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
