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Date: Sun, 26 Nov 2017 08:24:37 -0800 From: Dave Hansen <dave.hansen@...ux.intel.com> To: Andy Lutomirski <luto@...nel.org> Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, richard.fellner@...dent.tugraz.at, moritz.lipp@...k.tugraz.at, Daniel Gruss <daniel.gruss@...k.tugraz.at>, michael.schwarz@...k.tugraz.at, Linus Torvalds <torvalds@...ux-foundation.org>, Kees Cook <keescook@...gle.com>, Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org> Subject: Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch) On 11/26/2017 08:10 AM, Andy Lutomirski wrote: >> As a side benefit, this shouldn't have magical interactions with the >> vsyscall page any more. >> >> Are there cases that this would get wrong? >> > Quick ping: did this get lost? It does drop a warning that the other version of the code has, but that's pretty minor. Basically, we need two checks: pgd_userspace_access() (aka _PAGE_USER) and pgdp_maps_userspace() The original code does pgd_userspace_access() in a top-level if and then the pgdp_maps_userspace() checks at the second level. I think you are basically suggesting that we flip that. Logically, I'm sure we can make it work. It's just a matter of needing to look at other things first. BTW, this comment is, I think incorrect: > if (pgdp_maps_userspace(pgdp)) { ... > } else { > /* > * We can get here due to vmalloc, a vmalloc fault, memory > hot-add, or initial setup > * of kernelmode page tables. Regardless of which particular code > path we're in, > * these mappings should not be automatically propagated to the > usermode tables. > */ Since we pre-populated the entire kernel area's PGDs, I don't think we'll ever have a valid reason to be doing a set_pgd() again on the kernel area.
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