Re: [RFC PATCH 00/16] PTI support for x86-32

[Nadav Amit <nadav.amit@gmail.com>]

Please ignore my previous email. I got it working… Sorry for the spam.


Nadav Amit <nadav.amit@gmail.com> wrote:

> I am looking on PTI on x86-32, but I did not mange to get the PoC to work on
> this setup (kaslr disabled, similar setup works on 64-bit).
> 
> Did you use any PoC to “test” the protection?
> 
> Thanks,
> Nadav
> 
> 
> Joerg Roedel <joro@8bytes.org> wrote:
> 
>> From: Joerg Roedel <jroedel@suse.de>
>> 
>> Hi,
>> 
>> here is my current WIP code to enable PTI on x86-32. It is
>> still in a pretty early state, but it successfully boots my
>> KVM guest with PAE and with legacy paging. The existing PTI
>> code for x86-64 already prepares a lot of the stuff needed
>> for 32 bit too, thanks for that to all the people involved
>> in its development :)
>> 
>> The patches are split as follows:
>> 
>> 	- 1-3 contain the entry-code changes to enter and
>> 	  exit the kernel via the sysenter trampoline stack.
>> 
>> 	- 4-7 are fixes to get the code compile on 32 bit
>> 	  with CONFIG_PAGE_TABLE_ISOLATION=y.
>> 
>> 	- 8-14 adapt the existing PTI code to work properly
>> 	  on 32 bit and add the needed parts to 32 bit
>> 	  page-table code.
>> 
>> 	- 15 switches PTI on by adding the CR3 switches to
>> 	  kernel entry/exit.
>> 
>> 	- 16 enables the Kconfig for all of X86
>> 
>> The code has not run on bare-metal yet, I'll test that in
>> the next days once I setup a 32 bit box again. I also havn't
>> tested Wine and DosEMU yet, so this might also be broken.
>> 
>> With that post I'd like to ask for all kinds of constructive
>> feedback on the approaches I have taken and of course the
>> many things I broke with it :)
>> 
>> One of the things that are surely broken is XEN_PV support.
>> I'd appreciate any help with testing and bugfixing on that
>> front.
>> 
>> So please review and let me know your thoughts.
>> 
>> Thanks,
>> 
>> 	Joerg
>> 
>> Joerg Roedel (16):
>> x86/entry/32: Rename TSS_sysenter_sp0 to TSS_sysenter_stack
>> x86/entry/32: Enter the kernel via trampoline stack
>> x86/entry/32: Leave the kernel via the trampoline stack
>> x86/pti: Define X86_CR3_PTI_PCID_USER_BIT on x86_32
>> x86/pgtable: Move pgdp kernel/user conversion functions to pgtable.h
>> x86/mm/ldt: Reserve high address-space range for the LDT
>> x86/mm: Move two more functions from pgtable_64.h to pgtable.h
>> x86/pgtable/32: Allocate 8k page-tables when PTI is enabled
>> x86/mm/pti: Clone CPU_ENTRY_AREA on PMD level on x86_32
>> x86/mm/pti: Populate valid user pud entries
>> x86/mm/pgtable: Move pti_set_user_pgd() to pgtable.h
>> x86/mm/pae: Populate the user page-table with user pgd's
>> x86/mm/pti: Add an overflow check to pti_clone_pmds()
>> x86/mm/legacy: Populate the user page-table with user pgd's
>> x86/entry/32: Switch between kernel and user cr3 on entry/exit
>> x86/pti: Allow CONFIG_PAGE_TABLE_ISOLATION for x86_32
>> 
>> arch/x86/entry/entry_32.S               | 170 +++++++++++++++++++++++++++++---
>> arch/x86/include/asm/pgtable-2level.h   |   3 +
>> arch/x86/include/asm/pgtable-3level.h   |   3 +
>> arch/x86/include/asm/pgtable.h          |  88 +++++++++++++++++
>> arch/x86/include/asm/pgtable_32_types.h |   5 +-
>> arch/x86/include/asm/pgtable_64.h       |  85 ----------------
>> arch/x86/include/asm/processor-flags.h  |   8 +-
>> arch/x86/include/asm/switch_to.h        |   6 +-
>> arch/x86/kernel/asm-offsets_32.c        |   5 +-
>> arch/x86/kernel/cpu/common.c            |   5 +-
>> arch/x86/kernel/head_32.S               |  23 ++++-
>> arch/x86/kernel/process.c               |   2 -
>> arch/x86/kernel/process_32.c            |   6 ++
>> arch/x86/mm/pgtable.c                   |  11 ++-
>> arch/x86/mm/pti.c                       |  34 ++++++-
>> security/Kconfig                        |   2 +-
>> 16 files changed, 333 insertions(+), 123 deletions(-)
>> 
>> -- 
>> 2.13.6
>> 
>> --
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