linux-kernel - Re: [PATCH v2 17/39] mm: Fixup places that call pte

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Message-ID: <Y0mFqGvtSrw/kS4b@hirez.programming.kicks-ass.net>
Date:   Fri, 14 Oct 2022 17:52:08 +0200
From:   Peter Zijlstra <peterz@...radead.org>
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>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v2 17/39] mm: Fixup places that call pte_mkwrite()
 directly

On Thu, Sep 29, 2022 at 03:29:14PM -0700, Rick Edgecombe wrote:
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 7327b2573f7c..b49372c7de41 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -63,6 +63,7 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
>  	int ret;
>  	pte_t _dst_pte, *dst_pte;
>  	bool writable = dst_vma->vm_flags & VM_WRITE;
> +	bool shstk = dst_vma->vm_flags & VM_SHADOW_STACK;
>  	bool vm_shared = dst_vma->vm_flags & VM_SHARED;
>  	bool page_in_cache = page->mapping;
>  	spinlock_t *ptl;
> @@ -83,9 +84,12 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
>  		writable = false;
>  	}
>  
> -	if (writable)
> -		_dst_pte = pte_mkwrite(_dst_pte);
> -	else
> +	if (writable) {
> +		if (shstk)
> +			_dst_pte = pte_mkwrite_shstk(_dst_pte);
> +		else
> +			_dst_pte = pte_mkwrite(_dst_pte);
> +	} else
>  		/*
>  		 * We need this to make sure write bit removed; as mk_pte()
>  		 * could return a pte with write bit set.

Urgh.. that's unfortunate. But yeah, I don't see a way to make that
pretty either.