From: Bharata B Rao <bharata@xxxxxxx> > Sent: 10 March 2022 11:16 > > This patchset makes use of Upper Address Ignore (UAI) feature available > on upcoming AMD processors to provide user address tagging support for x86/AMD. > > UAI allows software to store a tag in the upper 7 bits of a logical > address [63:57]. When enabled, the processor will suppress the > traditional canonical address checks on the addresses. More information > about UAI can be found in section 5.10 of 'AMD64 Architecture > Programmer's Manual, Vol 2: System Programming' which is available from > > https://bugzilla.kernel.org/attachment.cgi?id=300549 Is that really allowing bit 63 to be used? That is normally the user-kernel bit. I can't help feeling that will just badly break things. Otherwise the best thing is just to change access_ok() to only reject addresses with the top bit set. Then you shouldn't need any extra tests in the fast-path of access_ok(). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
