linux-kernel - Re: [PATCH v7 21/41] mm: Add guard pages around a shadow stack.

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 for Android: free password hash cracker in your pocket

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

Message-ID: <f91bbe94b51c0855da921a770685aa17c06c8beb.camel@intel.com>
Date:   Tue, 7 Mar 2023 01:29:50 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "bp@...en8.de" <bp@...en8.de>
CC:     "david@...hat.com" <david@...hat.com>,
        "bsingharora@...il.com" <bsingharora@...il.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Syromiatnikov, Eugene" <esyr@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Eranian, Stephane" <eranian@...gle.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>,
        "pavel@....cz" <pavel@....cz>, "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>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Schimpe, Christina" <christina.schimpe@...el.com>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "debug@...osinc.com" <debug@...osinc.com>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "john.allen@....com" <john.allen@....com>,
        "rppt@...nel.org" <rppt@...nel.org>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "mingo@...hat.com" <mingo@...hat.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>
Subject: Re: [PATCH v7 21/41] mm: Add guard pages around a shadow stack.

On Mon, 2023-03-06 at 09:08 +0100, Borislav Petkov wrote:
> Just typos:

All seem reasonable to me. Thanks. 

For using the log verbiage for the comment, it is quite big. Does
something like this seem reasonable?

/*
 * The shadow stack pointer(SSP) is moved by CALL, RET, and INCSSPQ.
 * The INCSSP instruction can increment the shadow stack pointer. It
 * is the shadow stack analog of an instruction like:
 *
 *   addq $0x80, %rsp
 *
 * However, there is one important difference between an ADD on %rsp 
 * and INCSSP. In addition to modifying SSP, INCSSP also reads from the
 * memory of the first and last elements that were "popped". It can be
 * thought of as acting like this:
 *
 * READ_ONCE(ssp);       // read+discard top element on stack
 * ssp += nr_to_pop * 8; // move the shadow stack
 * READ_ONCE(ssp-8);     // read+discard last popped stack element
 *
 * The maximum distance INCSSP can move the SSP is 2040 bytes, before
 * it would read the memory. Therefore a single page gap will be enough
 * to prevent any operation from shifting the SSP to an adjacent stack,
 * since it would have to land in the gap at least once, causing a
 * fault.
 *
 * Prevent using INCSSP to move the SSP between shadow stacks by
 * having a PAGE_SIZE gaurd gap.
 */