linux-kernel - Re: [PATCH v3 15/37] x86/mm: Check Shadow Stack page fault errors

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y3S258Vtj63/fBsI@hirez.programming.kicks-ass.net>
Date:   Wed, 16 Nov 2022 11:09:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "bsingharora@...il.com" <bsingharora@...il.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Syromiatnikov, Eugene" <esyr@...hat.com>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        "Eranian, Stephane" <eranian@...gle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "nadav.amit@...il.com" <nadav.amit@...il.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "dethoma@...rosoft.com" <dethoma@...rosoft.com>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>, "oleg@...hat.com" <oleg@...hat.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "Yang, Weijiang" <weijiang.yang@...el.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "pavel@....cz" <pavel@....cz>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "rppt@...nel.org" <rppt@...nel.org>,
        "john.allen@....com" <john.allen@....com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "corbet@....net" <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "gorcunov@...il.com" <gorcunov@...il.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 15/37] x86/mm: Check Shadow Stack page fault errors

On Tue, Nov 15, 2022 at 11:13:34PM +0000, Edgecombe, Rick P wrote:

> When a page becomes COW it changes from a shadow stack permissioned
> page (Write=0,Dirty=1) to (Write=0,Dirty=0,CoW=1), which is simply
> read-only to the CPU. When shadow stack is enabled, a RET would
> normally pop the shadow stack by reading it with a "shadow stack read"
> access. However, in the COW case the shadow stack memory does not have
> shadow stack permissions, it is read-only. So it will generate a fault.
> 
> For conventionally writable pages, a read can be serviced with a read
> only PTE, and COW would not have to happen. But for shadow stack, there
> isn't the concept of read-only shadow stack memory. If it is shadow
> stack permissioned, it can be modified via CALL and RET instructions.
> So COW needs to happen before any memory can be mapped with shadow
> stack permissions.
> 
> Shadow stack accesses (read or write) need to be serviced with shadow
> stack permissioned memory, so in the case of a shadow stack read
> access, treat it as a WRITE fault so both COW will happen and the write
> fault path will tickle maybe_mkwrite() and map the memory shadow stack.

ACK.