From: Kees Cook <keescook@chromium.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
x86@kernel.org, Florian Weimer <fweimer@redhat.com>,
Jann Horn <jannh@google.com>
Subject: Re: [PATCH] mm/gup: Remove some BUG_ONs from get_gate_page()
Date: Thu, 27 Jun 2019 08:53:26 -0700 [thread overview]
Message-ID: <201906270853.CB6DA7BC8@keescook> (raw)
In-Reply-To: <a1d9f4efb75b9d464e59fd6af00104b21c58f6f7.1561610798.git.luto@kernel.org>
On Wed, Jun 26, 2019 at 09:47:30PM -0700, Andy Lutomirski wrote:
> If we end up without a PGD or PUD entry backing the gate area, don't
> BUG -- just fail gracefully.
>
> It's not entirely implausible that this could happen some day on
> x86. It doesn't right now even with an execute-only emulated
> vsyscall page because the fixmap shares the PUD, but the core mm
> code shouldn't rely on that particular detail to avoid OOPSing.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
> ---
> mm/gup.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index ddde097cf9e4..9883b598fd6f 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -585,11 +585,14 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
> pgd = pgd_offset_k(address);
> else
> pgd = pgd_offset_gate(mm, address);
> - BUG_ON(pgd_none(*pgd));
> + if (pgd_none(*pgd))
> + return -EFAULT;
> p4d = p4d_offset(pgd, address);
> - BUG_ON(p4d_none(*p4d));
> + if (p4d_none(*p4d))
> + return -EFAULT;
> pud = pud_offset(p4d, address);
> - BUG_ON(pud_none(*pud));
> + if (pud_none(*pud))
> + return -EFAULT;
> pmd = pmd_offset(pud, address);
> if (!pmd_present(*pmd))
> return -EFAULT;
> --
> 2.21.0
>
--
Kees Cook
prev parent reply other threads:[~2019-06-27 15:53 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-27 4:47 [PATCH] mm/gup: Remove some BUG_ONs from get_gate_page() Andy Lutomirski
2019-06-27 15:53 ` Kees Cook [this message]
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