Date: Tue, 12 Jul 2016 11:03:02 -0700 From: Andy Lutomirski <luto@...capital.net> To: Dave Hansen <dave.hansen@...el.com> Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, Borislav Petkov <bp@...en8.de>, Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jann@...jh.net>, Heiko Carstens <heiko.carstens@...ibm.com>, Andy Lutomirski <luto@...nel.org> Subject: Re: [PATCH v5 13/32] x86/mm/64: In vmalloc_fault(), use CR3 instead of current->active_mm On Tue, Jul 12, 2016 at 10:51 AM, Dave Hansen <dave.hansen@...el.com> wrote: > On 07/11/2016 01:53 PM, Andy Lutomirski wrote: >> If we get a vmalloc fault while current->active_mm->pgd doesn't >> match CR3, we'll crash without this change. I've seen this failure >> mode on heavily instrumented kernels with virtually mapped stacks. > > When does this happen, btw? Crossing page boundaries on the stack > between the time we swap mm's and the time we switch stacks? This can happen for any vmalloc fault between the mm swap and writing to current or current->active_mm. I hit it when playing with KASAN during the first clone. (KASAN has other issues, but this was one of them AFAICT.) --Andy
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