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Date: Fri, 17 Jun 2016 22:30:45 +0200
From: Borislav Petkov <bp@...en8.de>
To: Andy Lutomirski <luto@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, Nadav Amit <nadav.amit@...il.com>,
Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jann@...jh.net>,
Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v2 03/13] x86/cpa: Warn if kernel_unmap_pages_in_pgd is
used inappropriately
On Fri, Jun 17, 2016 at 01:00:39PM -0700, Andy Lutomirski wrote:
> It's currently only used in the EFI code, which is safe AFAICT.
"It is basically useful for a pagetable hierarchy which is not init_mm."
> Warn if anyone tries to use it on the normal kernel pgd.
>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
> arch/x86/mm/pageattr.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 6a8026918bf6..e9b9c5cedbb8 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -1996,6 +1996,9 @@ out:
> void kernel_unmap_pages_in_pgd(pgd_t *root, unsigned long address,
> unsigned numpages)
> {
> + /* Unmapping kernel entries from init_mm's pgd is not allowed. */
> + WARN_ON(root == init_mm.pgd);
We can also return and not do the unmapping:
if (WARN_ON(root == init_mm.pgd))
return;
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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