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Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization
Date 2017-03-24 11:40 +0100
Message-ID <touNr-aN-9@gated-at.bofh.it> (permalink)
References (1 earlier) <tosBY-79h-13@gated-at.bofh.it> <tosVj-7gO-1@gated-at.bofh.it> <tot4Z-7ku-5@gated-at.bofh.it> <totHH-7Sh-13@gated-at.bofh.it> <totRo-7Xq-23@gated-at.bofh.it>
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* Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:

> No. It is the firmware's EFI code, and the virtual translation applied by the OS 
> is made known to the firmware by means of a call into the runtime service 
> SetVirtualAddressMap(). This service can only be called once after each boot, 
> and so kexec kernels are forced to use the same VA mapping for runtime services 
> as the first kernel. This is the whole point of having a VA region reserved for 
> this, so that kexec kernels are guaranteed to be able to use the same VA 
> mapping.

Yes, but it's the kernel's EFI code that determines the area! So my suggestion:

> > Preserving virtual addresses for kexec is a red herring: the randomized offset 
> > could be passed to the kexec-ed kernel just fine.

Would solve the kexec problem, right?

I.e. the first kernel that boots randomizes the address range - and passes that 
offset off to any subsequent kernels.

Turning KASLR off actively degrades that randomization of the kernel virtual 
addresses.

Am I missing anything?

Thanks,

	Ingo

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[PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization Baoquan He <bhe@redhat.com> - 2017-03-24 06:10 +0100
  [tip:x86/urgent] x86/mm/KASLR: Exclude EFI region from KASLR VA  space randomization tip-bot for Baoquan He <tipbot@zytor.com> - 2017-03-24 09:20 +0100
  Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Ingo Molnar <mingo@kernel.org> - 2017-03-24 09:20 +0100
    Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Baoquan He <bhe@redhat.com> - 2017-03-24 09:40 +0100
      Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Dave Young <dyoung@redhat.com> - 2017-03-24 09:50 +0100
        Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Ingo Molnar <mingo@kernel.org> - 2017-03-24 10:30 +0100
          Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Borislav Petkov <bp@alien8.de> - 2017-03-24 10:40 +0100
          Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-03-24 10:40 +0100
            Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Borislav Petkov <bp@alien8.de> - 2017-03-24 10:50 +0100
              Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-03-24 11:00 +0100
            Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Borislav Petkov <bp@alien8.de> - 2017-03-24 10:50 +0100
              Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-03-24 10:50 +0100
            Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Ingo Molnar <mingo@kernel.org> - 2017-03-24 11:40 +0100
              Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-03-24 11:50 +0100
                Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Ingo Molnar <mingo@kernel.org> - 2017-03-24 12:00 +0100
          Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Baoquan He <bhe@redhat.com> - 2017-03-24 13:00 +0100
    Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into  KASLR VA space for randomization Dave Young <dyoung@redhat.com> - 2017-03-24 10:00 +0100

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