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Date: Thu, 24 Feb 2022 09:12:51 +0000 From: David Laight <David.Laight@...LAB.COM> To: 'Geert Uytterhoeven' <geert@...ux-m68k.org>, Kees Cook <keescook@...omium.org> CC: linux-m68k <linux-m68k@...ts.linux-m68k.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org> Subject: RE: [PATCH] m68k: Implement "current_stack_pointer" 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)
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