linux-kernel - Re: [PATCH] [v2] x86/doc: add PTI description

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Date:   Thu, 4 Jan 2018 21:32:22 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Hector Martin 'marcan' <marcan@...can.st>,
        linux-kernel@...r.kernel.org
Cc:     x86@...nel.org
Subject: Re: [PATCH] [v2] x86/doc: add PTI description

On 01/04/2018 05:43 PM, Hector Martin 'marcan' wrote:
> On 2018-01-05 09:24, Dave Hansen wrote:
>> +			Not specifying this option nothing is equivalent to
>> +			pti=auto.
> 
> -nothing

Sure, will fix.

>> +Page Table Isolation (pti, previously known as KAISER[1]) is a
>> +countermeasure against attacks on kernel address information such
>> +as the "Meltdown" approach[2].
> 
> It's not really just address information, but any data. Maybe "attacks
> that leak kernel memory"?

It's not just kernel leaks either, though.

>> +To avoid leaking address information, we create an new, independent
> 
> Same issue here. Also an -> a.

Will fix.

>> +copy of the page tables which are used only when running userspace
> 
> are -> is. The copy is singular.

I've reworded the sentence to remove the ambiguity.

>> +applications.  When the kernel is entered via syscalls, interrupts or
>> +exceptions, page tables are switched to the full "kernel" copy.  When
> 
> "the page tables".

No thanks.  It's fine the way it is.

>> +crippled by setting the NX bit in the top level.  This ensures
>> +that if a kernel->user CR3 switch is missed that userspace will
>> +crash immediately upon executing its first instruction.
> 
> "that userspace" -> "then userspace"