linux-kernel - Re: [PATCH 5/5] x86, pti: filter at vma->vm_page

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Message-ID: <30d4fd5a-a82f-2a94-e8cb-ad9b7d2dc5e7@linux.intel.com>
Date:   Mon, 23 Apr 2018 04:37:24 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Nadav Amit <namit@...are.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Dan Williams <dan.j.williams@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "keescook@...gle.com" <keescook@...gle.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...nel.org" <mingo@...nel.org>
Subject: Re: [PATCH 5/5] x86, pti: filter at vma->vm_page_prot population

On 04/20/2018 06:21 PM, Nadav Amit wrote:
>> pgprot_t vm_get_page_prot(unsigned long vm_flags)
>> {
>> -	return __pgprot(pgprot_val(protection_map[vm_flags &
>> +	pgprot_t ret = __pgprot(pgprot_val(protection_map[vm_flags &
>> 				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
>> 			pgprot_val(arch_vm_get_page_prot(vm_flags)));
>> +
>> +	return arch_filter_pgprot(ret);
>> }
>> EXPORT_SYMBOL(vm_get_page_prot);
> Wouldn’t it be simpler or at least cleaner to change the protection map if
> NX is not supported? I presume it can be done paging_init() similarly to the
> way other archs (e.g., arm, mips) do.

I thought about it, but doing it there requires getting the _timing_
right.  You have to do it before the protection map gets used but after
__supported_pte_mask is totally initialized.  This seemed more
straightforward, especially as a bug fix.

What you are talking about might be a good cleanup, though.