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[209.85.221.172]) by smtp.gmail.com with ESMTPSA id a26sm2935951vsq.29.2019.04.23.12.14.48 for (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Tue, 23 Apr 2019 12:14:48 -0700 (PDT) Received: by mail-vk1-f172.google.com with SMTP id x2so3455791vkx.13 for ; Tue, 23 Apr 2019 12:14:48 -0700 (PDT) X-Received: by 2002:a1f:7d8e:: with SMTP id y136mr8461809vkc.40.1556046888180; Tue, 23 Apr 2019 12:14:48 -0700 (PDT) MIME-Version: 1.0 References: <20190418154208.131118-1-glider@google.com> <20190418154208.131118-3-glider@google.com> <7bf6bd62-c8e0-df3d-8e98-70063f2d175a@intel.com> In-Reply-To: <7bf6bd62-c8e0-df3d-8e98-70063f2d175a@intel.com> From: Kees Cook Date: Tue, 23 Apr 2019 12:14:36 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 2/3] gfp: mm: introduce __GFP_NOINIT To: Dave Hansen Cc: Alexander Potapenko , Andrew Morton , Christoph Lameter , Dmitry Vyukov , Laura Abbott , Linux-MM , linux-security-module , Kernel Hardening Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Apr 18, 2019 at 9:52 AM Dave Hansen wrote: > > On 4/18/19 8:42 AM, Alexander Potapenko wrote: > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > > index be84f5f95c97..f9d1f1236cd0 100644 > > --- a/kernel/kexec_core.c > > +++ b/kernel/kexec_core.c > > @@ -302,7 +302,7 @@ static struct page *kimage_alloc_pages(gfp_t gfp_mask, unsigned int order) > > { > > struct page *pages; > > > > - pages = alloc_pages(gfp_mask & ~__GFP_ZERO, order); > > + pages = alloc_pages((gfp_mask & ~__GFP_ZERO) | __GFP_NOINIT, order); > > if (pages) { > > unsigned int count, i; > > While this is probably not super security-sensitive, it's also not > performance sensitive. It is, however, a pretty clear case of "and then we immediately zero it". > These sl*b ones seem like a bad idea. We already have rules that sl*b > allocations must be initialized by callers, and we have reasonably > frequent bugs where the rules are broken. Hm? No, this is saying that the page allocator can skip the auto-init because the slab internals will be doing it later. > Setting __GFP_NOINIT might be reasonable to do, though, for slabs that > have a constructor. We have much higher confidence that *those* are > going to get initialized properly. That's already handled in patch 1. -- Kees Cook