linux-kernel - Re: [RFC PATCH v9 16/27] mm: Update can_follow_write

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:   Wed, 26 Feb 2020 16:34:49 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>, 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>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>, x86-patch-review@...el.com
Subject: Re: [RFC PATCH v9 16/27] mm: Update can_follow_write_pte() for Shadow
 Stack

> +inline bool pte_exclusive(pte_t pte, struct vm_area_struct *vma)
> +{
> +	if (vma->vm_flags & VM_SHSTK)
> +		return pte_dirty_hw(pte);
> +	else
> +		return pte_dirty(pte);
> +}

I'm not really getting the naming.  What is exclusive?

> diff --git a/mm/gup.c b/mm/gup.c
> index 7646bf993b25..d1dbfbde8443 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -164,10 +164,12 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
>   * FOLL_FORCE can write to even unwritable pte's, but only
>   * after we've gone through a COW cycle and they are dirty.
>   */
> -static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
> +static inline bool can_follow_write(pte_t pte, unsigned int flags,
> +				    struct vm_area_struct *vma)

Having two identically named functions in two files in the same
subsystem seems like a recipe for confusion when I grep or cscope for
things.  It hardly seems worth the 4 characters of space savings IMNHO.

>  {
>  	return pte_write(pte) ||
> -		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
> +		((flags & FOLL_FORCE) && (flags & FOLL_COW) &&
> +		 pte_exclusive(pte, vma));
>  }

FWIW, this is the hunk that fixed DirtyCOW.

The least this deserves is acknowledgement of that in the changelog and
a missive about how you're sure you didn't just introduce
ShadowDirtyCOW.  Don't bother.  I already registered the domain. ;)