Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one whole page table in early boot code

From	Kees Cook <keescook@chromium.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one whole page table in early boot code
Date	2017-01-05 20:50 +0100
Message-ID	<sWmcV-7os-5@gated-at.bofh.it> (permalink)
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On Thu, Jan 5, 2017 at 6:01 AM, Borislav Petkov <bp@suse.de> wrote:
> On Thu, Jan 05, 2017 at 11:28:00AM +0800, Baoquan He wrote:
>> Possibly people worry more that no enough space left for kernel modules
>> mapping whthin 1G, just a guess. I am fine with making text mapping size
>> 1G by default. Kees must know more about the 1G only if kaslr enabled.
>
> So I'm thinking practically kaslr will be enabled on the majority
> of the systems anyway so we will have 1G text mapping size on most.
> The question is, are there any downsides/issues with making that the
> default.
>
> hpa, do you see any problems with it?

The only reason I had it as an option was for kernel module space. It
wasn't clear to me at the time if enough space remained for modules in
all use-cases. It seems like probably there is, so I have no objection
to making the mapping 1G unconditionally.

-Kees

-- 
Kees Cook
Nexus Security

Thread

[PATCH v3 0/3] Determine kernel image mapping size at runtime for x86_64 Baoquan He <bhe@redhat.com> - 2017-01-04 09:50 +0100
  [PATCH v3 1/3] x86/64: Make kernel text mapping always take one whole page table in early boot code Baoquan He <bhe@redhat.com> - 2017-01-04 09:50 +0100
    Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one whole page table in early boot code Boris Petkov <bp@suse.de> - 2017-01-04 16:50 +0100
      Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one  whole page table in early boot code Baoquan He <bhe@redhat.com> - 2017-01-05 04:30 +0100
        Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one  whole page table in early boot code Borislav Petkov <bp@suse.de> - 2017-01-05 15:20 +0100
          Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one  whole page table in early boot code Kees Cook <keescook@chromium.org> - 2017-01-05 20:50 +0100
            Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one  whole page table in early boot code Borislav Petkov <bp@suse.de> - 2017-01-05 22:00 +0100
              Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one  whole page table in early boot code Baoquan He <bhe@redhat.com> - 2017-01-06 10:40 +0100
  [PATCH v3 2/3] x86/64: Introduce a new constant KERNEL_MAPPING_SIZE Baoquan He <bhe@redhat.com> - 2017-01-04 09:50 +0100
  [PATCH v3 3/3] x86/64/KASLR: Determine the kernel mapping size at run time Baoquan He <bhe@redhat.com> - 2017-01-04 10:00 +0100

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