linux-kernel - Re: [PATCH v6 22/41] mm/mmap: Add shadow stack pages to memory accounting

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:   Mon, 20 Feb 2023 22:44:13 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "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>,
        "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>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "kcc@...gle.com" <kcc@...gle.com>, "pavel@....cz" <pavel@....cz>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "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>,
        "x86@...nel.org" <x86@...nel.org>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "Yang, Weijiang" <weijiang.yang@...el.com>,
        "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>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v6 22/41] mm/mmap: Add shadow stack pages to memory
 accounting

On Mon, 2023-02-20 at 13:58 +0100, David Hildenbrand wrote:
> On 18.02.23 22:14, Rick Edgecombe wrote:
> > From: Yu-cheng Yu <yu-cheng.yu@...el.com>
> > 
> > The x86 Control-flow Enforcement Technology (CET) feature includes
> > a new
> > type of memory called shadow stack. This shadow stack memory has
> > some
> > unusual properties, which requires some core mm changes to function
> > properly.
> > 
> > Account shadow stack pages to stack memory.
> > 
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> > Tested-by: Pengfei Xu <pengfei.xu@...el.com>
> > Tested-by: John Allen <john.allen@....com>
> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> > Co-developed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> > Cc: Kees Cook <keescook@...omium.org>
> > 
> > ---
> > v3:
> >    - Remove unneeded VM_SHADOW_STACK check in accountable_mapping()
> >      (Kirill)
> > 
> > v2:
> >    - Remove is_shadow_stack_mapping() and just change it to
> > directly bitwise
> >      and VM_SHADOW_STACK.
> > 
> > Yu-cheng v26:
> >    - Remove redundant #ifdef CONFIG_MMU.
> > 
> > Yu-cheng v25:
> >    - Remove #ifdef CONFIG_ARCH_HAS_SHADOW_STACK for
> > is_shadow_stack_mapping().
> > ---
> >    mm/mmap.c | 2 ++
> >    1 file changed, 2 insertions(+)
> > 
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 425a9349e610..9f85596cce31 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -3290,6 +3290,8 @@ void vm_stat_account(struct mm_struct *mm,
> > vm_flags_t flags, long npages)
> >                mm->exec_vm += npages;
> >        else if (is_stack_mapping(flags))
> >                mm->stack_vm += npages;
> > +     else if (flags & VM_SHADOW_STACK)
> > +             mm->stack_vm += npages;
> 
> Why not modify is_stack_mapping() ?

It kind of sticks out a little in this conditional, but
is_stack_mapping() has this comment:
/*
 * Stack area - automatically grows in one direction
 *
 * VM_GROWSUP / VM_GROWSDOWN VMAs are always private anonymous:
 * do_mmap() forbids all other combinations.
 */

Shadow stack don't grow, so it doesn't quite fit. There used to be an
is_shadow_stack_mapping(), but it was removed because all that was
needed (for the time being) was the simple bitwise AND:

https://lore.kernel.org/lkml/804adbac-61e6-0fd2-f726-5735fb290199@intel.com/