Re: Patch "x86/kexec: Allocate 8k PGDs for PTI" has been added to the 3.18-stable tree

[Hugh Dickins <hughd@google.com>]

On Mon, 17 Sep 2018, gregkh@linuxfoundation.org wrote:
> 
> This is a note to let you know that I've just added the patch titled
> 
>     x86/kexec: Allocate 8k PGDs for PTI
> 
> to the 3.18-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      x86-kexec-allocate-8k-pgds-for-pti.patch
> and it can be found in the queue-3.18 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.

I believe this commit is an example of the auto-selector being too
eager, and this should not be in *any* of the stable trees.  As the
commit message indicates, it's a fix by Joerg for his PTI-x86-32
implementation - which has not been backported to any of the stable
trees (yet), has it?

In several of the recent stable trees, I think this will not do any
actual harm; but it looks as if it will prevent relevant x86-32 configs
from building on 3.18 (I see no definition of PGD_ALLOCATION_ORDER in
linux-3.18.y - you preferred not to have any PTI in that tree), and I
haven't checked whether its definition in older backports will build
correctly here or not.

Hugh

> 
> 
> From foo@baz Mon Sep 17 11:45:57 CEST 2018
> From: Joerg Roedel <jroedel@suse.de>
> Date: Wed, 25 Jul 2018 17:48:03 +0200
> Subject: x86/kexec: Allocate 8k PGDs for PTI
> 
> From: Joerg Roedel <jroedel@suse.de>
> 
> [ Upstream commit ca38dc8f2724d101038b1205122c93a1c7f38f11 ]
> 
> Fuzzing the PTI-x86-32 code with trinity showed unhandled
> kernel paging request oops-messages that looked a lot like
> silent data corruption.
> 
> Lot's of debugging and testing lead to the kexec-32bit code,
> which is still allocating 4k PGDs when PTI is enabled. But
> since it uses native_set_pud() to build the page-table, it
> will unevitably call into __pti_set_user_pgtbl(), which
> writes beyond the allocated 4k page.
> 
> Use PGD_ALLOCATION_ORDER to allocate PGDs in the kexec code
> to fix the issue.
> 
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Tested-by: David H. Gutteridge <dhgutteridge@sympatico.ca>
> Cc: "H . Peter Anvin" <hpa@zytor.com>
> Cc: linux-mm@kvack.org
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Jiri Kosina <jkosina@suse.cz>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Brian Gerst <brgerst@gmail.com>
> Cc: David Laight <David.Laight@aculab.com>
> Cc: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: Eduardo Valentin <eduval@amazon.com>
> Cc: Greg KH <gregkh@linuxfoundation.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: aliguori@amazon.com
> Cc: daniel.gruss@iaik.tugraz.at
> Cc: hughd@google.com
> Cc: keescook@google.com
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Waiman Long <llong@redhat.com>
> Cc: Pavel Machek <pavel@ucw.cz>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Jiri Olsa <jolsa@redhat.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: joro@8bytes.org
> Link: https://lkml.kernel.org/r/1532533683-5988-4-git-send-email-joro@8bytes.org
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  arch/x86/kernel/machine_kexec_32.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> --- a/arch/x86/kernel/machine_kexec_32.c
> +++ b/arch/x86/kernel/machine_kexec_32.c
> @@ -69,7 +69,7 @@ static void load_segments(void)
>  
>  static void machine_kexec_free_page_tables(struct kimage *image)
>  {
> -	free_page((unsigned long)image->arch.pgd);
> +	free_pages((unsigned long)image->arch.pgd, PGD_ALLOCATION_ORDER);
>  	image->arch.pgd = NULL;
>  #ifdef CONFIG_X86_PAE
>  	free_page((unsigned long)image->arch.pmd0);
> @@ -85,7 +85,8 @@ static void machine_kexec_free_page_tabl
>  
>  static int machine_kexec_alloc_page_tables(struct kimage *image)
>  {
> -	image->arch.pgd = (pgd_t *)get_zeroed_page(GFP_KERNEL);
> +	image->arch.pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
> +						    PGD_ALLOCATION_ORDER);
>  #ifdef CONFIG_X86_PAE
>  	image->arch.pmd0 = (pmd_t *)get_zeroed_page(GFP_KERNEL);
>  	image->arch.pmd1 = (pmd_t *)get_zeroed_page(GFP_KERNEL);
> 
> 
> Patches currently in stable-queue which might be from jroedel@suse.de are
> 
> queue-3.18/x86-kexec-allocate-8k-pgds-for-pti.patch
> queue-3.18/x86-mm-remove-in_nmi-warning-from-vmalloc_fault.patch
>