RE: [PATCH 04/14] x86: use more conventional access_ok() definition
From: David Laight <hidden>
Date: 2022-02-14 22:13:43
Also in:
linux-alpha, linux-api, linux-arch, linux-m68k, linux-mm, linux-riscv, linux-s390, linux-sh, linux-um, linuxppc-dev, lkml, sparclinux
From: Linus Torvalds
Sent: 14 February 2022 20:24quoted
x86-64 has always(*) used TASK_SIZE_MAX for access_ok(), and the get_user() assembler implementation does the same.Side note: we could just check the sign bit instead, and avoid big constants that way.
The cheap test for most 64bit is (addr | size) >> 62 != 0. I did some tests last week and the compilers correctly optimise out constant size. Doesn't sparc64 still need a wrap test? Or is that assumed because there is always an unmapped page and transfer are 'adequately' done on increasing addresses? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)