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Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated

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On Fri, Jul 22, 2016 at 11:21 AM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Fri, Jul 22, 2016 at 3:21 AM, Ingo Molnar <mingo@kernel.org> wrote:
>>
>> * Andy Lutomirski <luto@kernel.org> wrote:
>>
>>> On 07/21/2016 09:43 PM, Valdis.Kletnieks@vt.edu wrote:
>>> >On Mon, 11 Jul 2016 13:53:36 -0700, Andy Lutomirski said:
>>> >>This avoids pointless races in which another CPU or task might see a
>>> >>partially populated global pgd entry.  These races should normally
>>> >>be harmless, but, if another CPU propagates the entry via
>>> >>vmalloc_fault and then populate_pgd fails (due to memory allocation
>>> >>failure, for example), this prevents a use-after-free of the pgd
>>> >>entry.
>>> >>
>>> >>Signed-off-by: Andy Lutomirski <luto@kernel.org>
>>> >>---
>>> >> arch/x86/mm/pageattr.c | 9 ++++++---
>>> >> 1 file changed, 6 insertions(+), 3 deletions(-)
>>> >
>>> >I just bisected a failure to boot down to this patch.  On my Dell Latitude
>>> >laptop, it results in the kernel being loaded and then just basically sitting
>>> >there dead in the water - as far as I can tell, it dies before the kernel
>>> >ever gets going far enough to do any console I/O (even with ignore_loglevel).
>>> >Nothing in /sys/fs/pstore either.  I admit not understanding the VM code
>>> >at all, so I don't have a clue *why* this causes indigestion...
>>> >
>>> >CPU is an Intel Core i5-3340M in case that matters....
>>> >
>>>
>>> How much memory do you have and what's your config?  My code is obviously
>>> buggy, but I'm wondering why neither I nor the 0day bot caught this.
>>>
>>> The attached patch is compile-tested only.  (Even Thunderbird doesn't want
>>> to send non-flowed text right now, sigh.)
>>>
>>> --Andy
>>
>>> From 6589ddf69a1369e1ecb95f0af489d90b980e256e Mon Sep 17 00:00:00 2001
>>> Message-Id: <6589ddf69a1369e1ecb95f0af489d90b980e256e.1469165371.git.luto@kernel.org>
>>> From: Andy Lutomirski <luto@kernel.org>
>>> Date: Thu, 21 Jul 2016 22:22:02 -0700
>>> Subject: [PATCH] x86/mm: Fix populate_pgd()
>>>
>>> I make an obvious error in populate_pgd() -- it would fail to correctly
>>> populate the page tables when it allocated a new pud page.
>>
>> JFYI, on allnoconfig it gives:
>>
>>   arch/x86/mm/pageattr.c:1016:20: error: implicit declaration of function ‘pud_index’ [-Werror=implicit-function-declaration]
>
> As it happens, my fix interacts badly with the steaming pile of crap
> that is Linux's support for <4 page table levels.  Can you just revert
> the offending patch and I'll redo it differently?

No, don't revert it.  The result doesn't work.  I'll send something.

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[PATCH v5 00/32] virtually mapped stacks and thread_info cleanup Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 18/32] signal: Consolidate {TS,TLF}_RESTORE_SIGMASK code Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
    Re: [PATCH v5 18/32] signal: Consolidate {TS,TLF}_RESTORE_SIGMASK code Brian Gerst <brgerst@gmail.com> - 2016-07-12 14:00 +0200
      Re: [PATCH v5 18/32] signal: Consolidate {TS,TLF}_RESTORE_SIGMASK code Andy Lutomirski <luto@amacapital.net> - 2016-07-13 01:10 +0200
  [PATCH v5 08/32] dma-api: Teach the "DMA-from-stack" check about vmapped stacks Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 32/32] fork: Cache two thread stacks per cpu if CONFIG_VMAP_STACK is set Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 27/32] x86: Move thread_info into task_struct Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 31/32] sched: Free the stack early if CONFIG_THREAD_INFO_IN_TASK Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 23/32] printk: When dumping regs, show the stack, not thread_info Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 19/32] x86/smp: Remove stack_smp_processor_id() Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 20/32] x86/smp: Remove unnecessary initialization of thread_info::cpu Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 16/32] x86: Move uaccess_err and sig_on_uaccess_err to thread_struct Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:00 +0200
  [PATCH v5 04/32] x86/mm: Remove kernel_unmap_pages_in_pgd() and efi_cleanup_page_tables() Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
  [PATCH v5 01/32] bluetooth: Switch SMP to crypto_cipher_encrypt_one() Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
    Re: [PATCH v5 01/32] bluetooth: Switch SMP to crypto_cipher_encrypt_one() Andy Lutomirski <luto@amacapital.net> - 2016-07-14 21:20 +0200
      Re: [PATCH v5 01/32] bluetooth: Switch SMP to crypto_cipher_encrypt_one() Marcel Holtmann <marcel@holtmann.org> - 2016-07-14 22:40 +0200
      Re: [PATCH v5 01/32] bluetooth: Switch SMP to  crypto_cipher_encrypt_one() David Miller <davem@davemloft.net> - 2016-07-14 22:50 +0200
  [PATCH v5 05/32] mm: Track NR_KERNEL_STACK in KiB instead of number of stacks Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
  [PATCH v5 12/32] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
  [PATCH v5 06/32] mm: Fix memcg stack accounting for sub-page stacks Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
  [PATCH v5 03/32] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
    Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated Valdis.Kletnieks@vt.edu - 2016-07-22 06:50 +0200
      Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd,  don't set the pgd entry until it's populated Andy Lutomirski <luto@kernel.org> - 2016-07-22 07:40 +0200
        Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd,  don't set the pgd entry until it's populated Ingo Molnar <mingo@kernel.org> - 2016-07-22 12:30 +0200
          Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd,  don't set the pgd entry until it's populated Andy Lutomirski <luto@amacapital.net> - 2016-07-22 20:30 +0200
            Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd,  don't set the pgd entry until it's populated Andy Lutomirski <luto@amacapital.net> - 2016-07-22 20:40 +0200
            Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd,  don't set the pgd entry until it's populated Ingo Molnar <mingo@kernel.org> - 2016-07-22 22:20 +0200
        Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated Nicolai Stange <nicstange@gmail.com> - 2016-07-23 17:00 +0200
  [PATCH v5 10/32] x86/dumpstack: Honor supplied @regs arg Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
  [PATCH v5 02/32] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable() Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
  [PATCH v5 15/32] x86/mm: Improve stack-overflow #PF handling Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
  [PATCH v5 11/32] x86/dumpstack: Try harder to get a call trace on stack overflow Andy Lutomirski <luto@kernel.org> - 2016-07-11 23:10 +0200
  Re: [PATCH v5 00/32] virtually mapped stacks and thread_info cleanup Herbert Xu <herbert@gondor.apana.org.au> - 2016-07-12 11:00 +0200
  Re: [PATCH v5 00/32] virtually mapped stacks and thread_info cleanup Christian Borntraeger <borntraeger@de.ibm.com> - 2016-07-13 11:00 +0200
    Re: [PATCH v5 00/32] virtually mapped stacks and thread_info cleanup Andy Lutomirski <luto@amacapital.net> - 2016-07-13 20:40 +0200
      Re: [PATCH v5 00/32] virtually mapped stacks and thread_info cleanup Christian Borntraeger <borntraeger@de.ibm.com> - 2016-07-13 21:00 +0200

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