Messages in this thread | | | Date | Thu, 12 May 2022 16:23:48 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFCv2 05/10] x86/mm: Provide untagged_addr() helper |
| |
On Thu, May 12, 2022 at 03:06:38PM +0200, Thomas Gleixner wrote:
> #define untagged_addr(addr) ({ \ > u64 __addr = (__force u64)(addr); \ > \ > __addr &= current->thread.lam_untag_mask; \ > (__force __typeof__(addr))__addr; \ > }) > > No conditionals, fast _and_ correct. Setting this untag mask up once > when LAM is enabled is not rocket science.
But that goes wrong if someone ever wants to untag a kernel address and not use the result for access_ok().
I'd feel better about something like:
s64 __addr = (addr); s64 __sign = __addr;
__sign >>= 63; __sign &= lam_untag_mask; __addr &= lam_untag_mask; __addr |= __sign;
__addr;
Which simply extends bit 63 downwards -- although possibly there's an easier way to do that, this is pretty gross.
| |