linux-kernel - Re: [PATCH v7 24/41] mm: Don't allow write GUPs to shadow stack memory

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Message-ID: <CAKC1njRh8zz9jUM3xwCeZ1hs9K8o=mF8VKTsYyG73a5tTe4FkA@mail.gmail.com>
Date:   Fri, 17 Mar 2023 10:05:19 -0700
From:   Deepak Gupta <debug@...osinc.com>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Allen <john.allen@....com>, kcc@...gle.com,
        eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, akpm@...ux-foundation.org,
        Andrew.Cooper3@...rix.com, christina.schimpe@...el.com,
        david@...hat.com
Subject: Re: [PATCH v7 24/41] mm: Don't allow write GUPs to shadow stack memory

On Mon, Feb 27, 2023 at 2:31 PM Rick Edgecombe
<rick.p.edgecombe@...el.com> wrote:
> diff --git a/mm/gup.c b/mm/gup.c
> index eab18ba045db..e7c7bcc0e268 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -978,7 +978,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
>                 return -EFAULT;
>
>         if (write) {
> -               if (!(vm_flags & VM_WRITE)) {
> +               if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) {

I think I missed this in the review.
`VM_SHADOW_STACK` is an x86 specific vmaflag to represent a shadow stack VMA.
Since this is arch agnostic code. Can we instead have
`is_arch_shadow_stack_vma` which consumes vma flags and returns true.
This allows different architectures to choose whatever encoding of the
vma flag to represent a shadow stack.


>                         if (!(gup_flags & FOLL_FORCE))
>                                 return -EFAULT;
>                         /* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */
> --
> 2.17.1
>