Re: [tip:efi/core] x86/efi: Unmap EFI boot services code/data regions from efi_pgd

From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>,
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Subject: Re: [tip:efi/core] x86/efi: Unmap EFI boot services code/data regions from efi_pgd
Date: Mon, 17 Dec 2018 19:10:58 +0100	[thread overview]
Message-ID: <CAKv+Gu_vTHFxpKRu_CxKP-GdNdgdFKr7fi87VkNur0sqGQNVDw@mail.gmail.com> (raw)
In-Reply-To: <FFF73D592F13FD46B8700F0A279B802F48604575@ORSMSX114.amr.corp.intel.com>

On Mon, 17 Dec 2018 at 19:06, Prakhya, Sai Praneeth
<sai.praneeth.prakhya@intel.com> wrote:
>
> > Commit-ID:  08cfb38f3ef49cfd1bba11a00401451606477d80
> > Gitweb:
> > https://git.kernel.org/tip/08cfb38f3ef49cfd1bba11a00401451606477d80
> > Author:     Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> > AuthorDate: Thu, 29 Nov 2018 18:12:24 +0100
> > Committer:  Ingo Molnar <mingo@kernel.org>
> > CommitDate: Fri, 30 Nov 2018 09:10:30 +0100
> >
> > x86/efi: Unmap EFI boot services code/data regions from efi_pgd
> >
> > efi_free_boot_services(), as the name suggests, frees EFI boot services
> > code/data regions but forgets to unmap these regions from efi_pgd. This means
> > that any code that's running in efi_pgd address space (e.g:
> > any EFI runtime service) would still be able to access these regions but the
> > contents of these regions would have long been over written by someone else.
> > So, it's important to unmap these regions. Hence, introduce efi_unmap_pages()
> > to unmap these regions from efi_pgd.
> >
> > After unmapping EFI boot services code/data regions, any illegal access by
> > buggy firmware to these regions would result in page fault which will be handled
> > by EFI specific fault handler.
>
> Hi Thomas and Ingo,
>
> I recently noticed that the below commits [1] and [2] are broken when kernel command line
> argument "efi=old_map" is passed. Sorry! I missed to test this condition prior to sending
> these patches to mailing list. I am working on a fix and will send it to mailing list as
> soon as it's ready.
>

Could you elaborate on the problem please?

> Meanwhile, could you please drop these patches before sending pull request to Linus?
>
> [1] Commit 08cfb38f3ef4 ("x86/efi: Unmap EFI boot services code/data regions from efi_pgd")
> [2] Commit 7e0dabd3010d ("x86/mm/pageattr: Introduce helper function to unmap EFI boot services")
>

I'd like to understand what the issue is before we drop anything.