linux-kernel - Re: [PATCH 2/2] x86, pti: fix boot warning from Global-bit setting

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Date:   Tue, 17 Apr 2018 23:56:36 +0200
From:   Mariusz Ceier <mceier+kernel@...il.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, Aaro Koskinen <aaro.koskinen@...ia.com>,
        aarcange@...hat.com, luto@...nel.org, arjan@...ux.intel.com,
        Borislav Petkov <bp@...en8.de>, dan.j.williams@...el.com,
        dwmw2@...radead.org, gregkh@...uxfoundation.org, hughd@...gle.com,
        jpoimboe@...hat.com, jgross@...e.com, keescook@...gle.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        namit@...are.com, peterz@...radead.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] x86, pti: fix boot warning from Global-bit setting

On 17 April 2018 at 23:13, Dave Hansen <dave.hansen@...ux.intel.com> wrote:
>
> These are _very_ lightly tested.  I'm throwing them out there for
> folks are looking for a fix.
>
> ---
>
> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> pageattr.c is not friendly when it encounters empty (zero) PTEs.  The
> kernel linear map is exempt from these checks, but kernel text is not.
> This patch adds the code to also exempt kernel text from these checks.
> The proximate cause of these warnings was most likely an __init area
> that spanned a 2MB page boundary that resulted in a "zero" PMD.
>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Fixes: 39114b7a7 (x86/pti: Never implicitly clear _PAGE_GLOBAL for kernel image)
> Reported-by: Mariusz Ceier <mceier@...il.com>
> Reported-by: Aaro Koskinen <aaro.koskinen@...ia.com>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Arjan van de Ven <arjan@...ux.intel.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: David Woodhouse <dwmw2@...radead.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Kees Cook <keescook@...gle.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Nadav Amit <namit@...are.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: linux-mm@...ck.org
> ---
>
>  b/arch/x86/mm/pageattr.c |   17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff -puN arch/x86/mm/pageattr.c~pti-glb-warning-inpageattr arch/x86/mm/pageattr.c
> --- a/arch/x86/mm/pageattr.c~pti-glb-warning-inpageattr 2018-04-17 14:10:22.695395554 -0700
> +++ b/arch/x86/mm/pageattr.c    2018-04-17 14:10:22.721395554 -0700
> @@ -1151,6 +1151,16 @@ static int populate_pgd(struct cpa_data
>         return 0;
>  }
>
> +bool __cpa_pfn_in_highmap(unsigned long pfn)
> +{
> +       /*
> +        * Kernel text has an alias mapping at a high address, known
> +        * here as "highmap".
> +        */
> +       return within_inclusive(pfn, highmap_start_pfn(),
> +                       highmap_end_pfn());
> +}
> +
>  static int __cpa_process_fault(struct cpa_data *cpa, unsigned long vaddr,
>                                int primary)
>  {
> @@ -1183,6 +1193,10 @@ static int __cpa_process_fault(struct cp
>                 cpa->numpages = 1;
>                 cpa->pfn = __pa(vaddr) >> PAGE_SHIFT;
>                 return 0;
> +
> +       } else if (__cpa_pfn_in_highmap(cpa->pfn)) {
> +               /* Faults in the highmap are OK, so do not warn: */
> +               return -EFAULT;
>         } else {
>                 WARN(1, KERN_WARNING "CPA: called for zero pte. "
>                         "vaddr = %lx cpa->vaddr = %lx\n", vaddr,
> @@ -1335,8 +1349,7 @@ static int cpa_process_alias(struct cpa_
>          * to touch the high mapped kernel as well:
>          */
>         if (!within(vaddr, (unsigned long)_text, _brk_end) &&
> -           within_inclusive(cpa->pfn, highmap_start_pfn(),
> -                            highmap_end_pfn())) {
> +           __cpa_pfn_in_highmap(cpa->pfn)) {
>                 unsigned long temp_cpa_vaddr = (cpa->pfn << PAGE_SHIFT) +
>                                                __START_KERNEL_map - phys_base;
>                 alias_cpa = *cpa;
> _


I confirm that these 2 patches fix the BUG for me in kernel 4.17.0-rc1.

Thanks