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From: Kees Cook <keescook@google.com>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
	Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Rik van Riel <riel@redhat.com>,
	Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
	Hugh Dickins <hughd@google.com>, Linux-MM <linux-mm@kvack.org>,
	michael.schwarz@iaik.tugraz.at, moritz.lipp@iaik.tugraz.at,
	richard.fellner@student.tugraz.at
Subject: Re: [patch V2 1/5] x86/kaiser: Respect disabled CPU features
Date: Mon, 27 Nov 2017 10:37:19 -0800	[thread overview]
Message-ID: <CAGXu5jKyx1T+NZGgPUUPt_-MqZe3-zrpFbAVFzsWbW=aD-D6_Q@mail.gmail.com> (raw)
In-Reply-To: <07d101b3-d17a-7781-f05e-96738e6d6848@linux.intel.com>

On Mon, Nov 27, 2017 at 10:11 AM, Dave Hansen
<dave.hansen@linux.intel.com> wrote:
>> --- a/arch/x86/include/asm/pgtable_64.h
>> +++ b/arch/x86/include/asm/pgtable_64.h
>> @@ -222,7 +222,8 @@ static inline pgd_t kaiser_set_shadow_pg
>>                        * wrong CR3 value, userspace will crash
>>                        * instead of running.
>>                        */
>> -                     pgd.pgd |= _PAGE_NX;
>> +                     if (__supported_pte_mask & _PAGE_NX)
>> +                             pgd.pgd |= _PAGE_NX;
>>               }
>
> Thanks for catching that.  It's definitely a bug.  Although,
> practically, it's hard to hit, right?  I think everything 64-bit
> supports NX unless the hypervisor disabled it or something.

There was a very narrow window where x86_64 machines were made without
NX. :( This is reflected in x86_report_nx(), though maybe we should
add a "OMG, why?" when 64-bit but no NX. ;)

-Kees

-- 
Kees Cook
Pixel Security

WARNING: multiple messages have this Message-ID
From: Kees Cook <keescook@google.com>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
	Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Rik van Riel <riel@redhat.com>,
	Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
	Hugh Dickins <hughd@google.com>, Linux-MM <linux-mm@kvack.org>,
	michael.schwarz@iaik.tugraz.at, moritz.lipp@iaik.tugraz.at,
	richard.fellner@student.tugraz.at
Subject: Re: [patch V2 1/5] x86/kaiser: Respect disabled CPU features
Date: Mon, 27 Nov 2017 10:37:19 -0800	[thread overview]
Message-ID: <CAGXu5jKyx1T+NZGgPUUPt_-MqZe3-zrpFbAVFzsWbW=aD-D6_Q@mail.gmail.com> (raw)
In-Reply-To: <07d101b3-d17a-7781-f05e-96738e6d6848@linux.intel.com>

On Mon, Nov 27, 2017 at 10:11 AM, Dave Hansen
<dave.hansen@linux.intel.com> wrote:
>> --- a/arch/x86/include/asm/pgtable_64.h
>> +++ b/arch/x86/include/asm/pgtable_64.h
>> @@ -222,7 +222,8 @@ static inline pgd_t kaiser_set_shadow_pg
>>                        * wrong CR3 value, userspace will crash
>>                        * instead of running.
>>                        */
>> -                     pgd.pgd |= _PAGE_NX;
>> +                     if (__supported_pte_mask & _PAGE_NX)
>> +                             pgd.pgd |= _PAGE_NX;
>>               }
>
> Thanks for catching that.  It's definitely a bug.  Although,
> practically, it's hard to hit, right?  I think everything 64-bit
> supports NX unless the hypervisor disabled it or something.

There was a very narrow window where x86_64 machines were made without
NX. :( This is reflected in x86_report_nx(), though maybe we should
add a "OMG, why?" when 64-bit but no NX. ;)

-Kees

-- 
Kees Cook
Pixel Security

--
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  reply	other threads:[~2017-11-27 18:37 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-26 23:14 [patch V2 0/5] x86/kaiser: Boot time disabling and debug support Thomas Gleixner
2017-11-26 23:14 ` Thomas Gleixner
2017-11-26 23:14 ` [patch V2 1/5] x86/kaiser: Respect disabled CPU features Thomas Gleixner
2017-11-26 23:14   ` Thomas Gleixner
2017-11-27  9:57   ` Peter Zijlstra
2017-11-27  9:57     ` Peter Zijlstra
2017-11-27 11:47     ` Thomas Gleixner
2017-11-27 11:47       ` Thomas Gleixner
2017-11-27 12:31       ` Brian Gerst
2017-11-27 12:31         ` Brian Gerst
2017-11-27 13:18         ` Thomas Gleixner
2017-11-27 13:18           ` Thomas Gleixner
2017-11-27 18:11   ` Dave Hansen
2017-11-27 18:11     ` Dave Hansen
2017-11-27 18:37     ` Kees Cook [this message]
2017-11-27 18:37       ` Kees Cook
2017-11-26 23:14 ` [patch V2 2/5] x86/kaiser: Simplify disabling of global pages Thomas Gleixner
2017-11-26 23:14   ` Thomas Gleixner
2017-11-27 11:49   ` Thomas Gleixner
2017-11-27 11:49     ` Thomas Gleixner
2017-11-27 18:15   ` Dave Hansen
2017-11-27 18:15     ` Dave Hansen
2017-11-27 20:28     ` Thomas Gleixner
2017-11-27 20:28       ` Thomas Gleixner
2017-11-26 23:14 ` [patch V2 3/5] x86/dump_pagetables: Check KAISER shadow page table for WX pages Thomas Gleixner
2017-11-26 23:14   ` Thomas Gleixner
2017-11-27 18:17   ` Dave Hansen
2017-11-27 18:17     ` Dave Hansen
2017-11-26 23:14 ` [patch V2 4/5] x86/mm/debug_pagetables: Allow dumping current pagetables Thomas Gleixner
2017-11-26 23:14   ` Thomas Gleixner
2017-11-27  9:41   ` Peter Zijlstra
2017-11-27  9:41     ` Peter Zijlstra
2017-11-27 10:06     ` [PATCH] vfs: Add PERM_* symbolic helpers for common file mode/permissions Ingo Molnar
2017-11-27 10:06       ` Ingo Molnar
2017-11-27 19:21       ` Linus Torvalds
2017-11-27 19:21         ` Linus Torvalds
2017-11-28 10:54         ` Ingo Molnar
2017-11-28 10:54           ` Ingo Molnar
2017-11-28 11:12         ` Ingo Molnar
2017-11-28 11:12           ` Ingo Molnar
2017-11-29  8:52           ` Michael Ellerman
2017-11-29  8:52             ` Michael Ellerman
2017-11-27 18:18   ` [patch V2 4/5] x86/mm/debug_pagetables: Allow dumping current pagetables Dave Hansen
2017-11-27 18:18     ` Dave Hansen
2017-11-26 23:14 ` [patch V2 5/5] x86/kaiser: Add boottime disable switch Thomas Gleixner
2017-11-26 23:14   ` Thomas Gleixner
2017-11-27  9:48   ` Peter Zijlstra
2017-11-27  9:48     ` Peter Zijlstra
2017-11-27 10:22     ` Peter Zijlstra
2017-11-27 10:22       ` Peter Zijlstra
2017-11-27 11:50       ` Thomas Gleixner
2017-11-27 11:50         ` Thomas Gleixner
2017-11-27 12:49         ` Peter Zijlstra
2017-11-27 12:49           ` Peter Zijlstra
2017-11-27 21:43       ` Peter Zijlstra
2017-11-27 21:43         ` Peter Zijlstra
2017-11-27 18:22   ` Dave Hansen
2017-11-27 18:22     ` Dave Hansen
2017-11-27 19:00     ` Thomas Gleixner
2017-11-27 19:00       ` Thomas Gleixner
2017-11-27 19:18       ` Josh Poimboeuf
2017-11-27 19:18         ` Josh Poimboeuf
2017-11-27 20:47         ` Thomas Gleixner
2017-11-27 20:47           ` Thomas Gleixner

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