linux-kernel - RE: [tip:efi/core] x86/efi: Unmap EFI boot services code/data regions from efi

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Message-ID: <FFF73D592F13FD46B8700F0A279B802F48604575@ORSMSX114.amr.corp.intel.com>
Date:   Mon, 17 Dec 2018 18:06:54 +0000
From:   "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>
To:     Ingo Molnar <mingo@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "bp@...en8.de" <bp@...en8.de>,
        "marc.zyngier@....com" <marc.zyngier@....com>,
        "eric.snowberg@...cle.com" <eric.snowberg@...cle.com>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>,
        "arend.vanspriel@...adcom.com" <arend.vanspriel@...adcom.com>,
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        "luto@...nel.org" <luto@...nel.org>,
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        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>
Subject: RE: [tip:efi/core] x86/efi: Unmap EFI boot services code/data
 regions from efi_pgd

> Commit-ID:  08cfb38f3ef49cfd1bba11a00401451606477d80
> Gitweb:
> https://git.kernel.org/tip/08cfb38f3ef49cfd1bba11a00401451606477d80
> Author:     Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
> AuthorDate: Thu, 29 Nov 2018 18:12:24 +0100
> Committer:  Ingo Molnar <mingo@...nel.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.

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")

Regards,
Sai