From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [RFC PATCH v2 11/15] khwasan, mm: perform untagged pointers comparison in krealloc Date: Sat, 24 Mar 2018 09:29:47 +0100 Message-ID: <20180324082947.3isostkpsjraefqt@gmail.com> References: <6eb08c160ae23eb890bd937ddf8346ba211df09f.1521828274.git.andreyknvl@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 7C99B4A045 for ; Sat, 24 Mar 2018 04:22:15 -0400 (EDT) Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id QP6xxj7Po5a5 for ; Sat, 24 Mar 2018 04:21:54 -0400 (EDT) Received: from mail-wm0-f68.google.com (mail-wm0-f68.google.com [74.125.82.68]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id D96C74A01F for ; Sat, 24 Mar 2018 04:21:53 -0400 (EDT) Received: by mail-wm0-f68.google.com with SMTP id t6so7263312wmt.5 for ; Sat, 24 Mar 2018 01:29:52 -0700 (PDT) Content-Disposition: inline In-Reply-To: <6eb08c160ae23eb890bd937ddf8346ba211df09f.1521828274.git.andreyknvl@google.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: Andrey Konovalov Cc: Julien Thierry , Catalin Marinas , Christopher Li , Tyler Baicar , Will Deacon , Paul Lawrence , Masahiro Yamada , Yury Norov , Alexander Potapenko , Christoph Lameter , Michael Weiser , kvmarm@lists.cs.columbia.edu, Kees Cook , Herbert Xu , Jonathan Corbet , linux-doc@vger.kernel.org, Mark Brand , kasan-dev@googlegroups.com, linux-sparse@vger.kernel.org, Geert Uytterhoeven , linux-arm-kernel@lists.infradead.org, David Rientjes , Andrey Ryabinin , Ramana List-Id: kvmarm@lists.cs.columbia.edu * Andrey Konovalov wrote: > The krealloc function checks where the same buffer was reused or a new one > allocated by comparing kernel pointers. KHWASAN changes memory tag on the > krealloc'ed chunk of memory and therefore also changes the pointer tag of > the returned pointer. Therefore we need to perform comparison on untagged > (with tags reset) pointers to check whether it's the same memory region or > not. > > Signed-off-by: Andrey Konovalov > --- > mm/slab_common.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index a33e61315ca6..5911f2194cf7 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1494,7 +1494,7 @@ void *krealloc(const void *p, size_t new_size, gfp_t flags) > } > > ret = __do_krealloc(p, new_size, flags); > - if (ret && p != ret) > + if (ret && khwasan_reset_tag(p) != khwasan_reset_tag(ret)) > kfree(p); Small nit: If 'reset' here means an all zeroes tag (upper byte) then khwasan_clear_tag() might be a slightly easier to read primitive? Thanks, Ingo