linux-kernel - Re: [PATCH v3 20/37] mm/mprotect: Exclude shadow stack from preserve

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]

Date:   Tue, 15 Nov 2022 20:41:05 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>
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>,
        "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>,
        "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>,
        "pavel@....cz" <pavel@....cz>, "arnd@...db.de" <arnd@...db.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "john.allen@....com" <john.allen@....com>,
        "rppt@...nel.org" <rppt@...nel.org>,
        "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 20/37] mm/mprotect: Exclude shadow stack from
 preserve_write

On Tue, 2022-11-15 at 13:05 +0100, Peter Zijlstra wrote:
> On Fri, Nov 04, 2022 at 03:35:47PM -0700, Rick Edgecombe wrote:
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 73b9b78f8cf4..7643a4db1b50 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1803,6 +1803,13 @@ int change_huge_pmd(struct mmu_gather *tlb,
> > struct vm_area_struct *vma,
> >                return 0;
> >   
> >        preserve_write = prot_numa && pmd_write(*pmd);
> > +
> > +     /*
> > +      * Preserve only normal writable huge PMD, but not shadow
> > +      * stack (RW=0, Dirty=1).
> > +      */
> > +     if (vma->vm_flags & VM_SHADOW_STACK)
> > +             preserve_write = false;
> >        ret = 1;
> >   
> >   #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> > diff --git a/mm/mprotect.c b/mm/mprotect.c
> > index 668bfaa6ed2a..ea82ce5f38fe 100644
> > --- a/mm/mprotect.c
> > +++ b/mm/mprotect.c
> > @@ -115,6 +115,13 @@ static unsigned long change_pte_range(struct
> > mmu_gather *tlb,
> >                        pte_t ptent;
> >                        bool preserve_write = prot_numa &&
> > pte_write(oldpte);
> >   
> > +                     /*
> > +                      * Preserve only normal writable PTE, but not
> > shadow
> > +                      * stack (RW=0, Dirty=1).
> > +                      */
> > +                     if (vma->vm_flags & VM_SHADOW_STACK)
> > +                             preserve_write = false;
> > +
> >                        /*
> >                         * Avoid trapping faults against the zero or
> > KSM
> >                         * pages. See similar comment in
> > change_huge_pmd.
> 
> These comments lack a why component; someone is going to wonder wtf
> this
> code is doing in the near future -- that someone might be you.

Good point, I'll expand it.