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[209.85.220.65]) by mx.google.com with SMTPS id m94sor753939uam.55.2019.05.29.22.21.36 for (Google Transport Security); Wed, 29 May 2019 22:21:36 -0700 (PDT) Received-SPF: pass (google.com: domain of dianzhangchen0@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=nOfp6xAb; spf=pass (google.com: domain of dianzhangchen0@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=dianzhangchen0@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=N8Kqu9XhDk4eyHxJOCvnDVEeURLn9nIM7WXDv7rJ8RQ=; b=nOfp6xAb07c7fhTyEPViJQwkSTSfmWU/+klmqnkI9vWOtbvMhwszY6GFh6ufjBdu7g lpAq4QP0/Cufz4WaULPfWsua/GesqDG2HDvXk+NuUgfQhTvzxOdjgBniDIDnyRqY+4fc An+1RHMH7FDXq/dua0p+KM1Wew9m4jHnfDye9QEjShQPodvTTw4FEv0fxvn2El8x5kYE u7wJAhoUmz/cK93kAVTxiCQyxdHucxSw2pHYN8eV3W/n4u9DHZgjW8VbNnVhqIJV20Tq LXlRJ1w0Pc3GwDkob5jfDxszTaaQka77OPeVhsoOcZ8gO8m8HX1jb2INfcKGvedR7Q4R 6U9g== X-Google-Smtp-Source: APXvYqyBATh4neWGs74AqOJks4aL5K6flzPg8l6Xjw6Lgiu2KpqI9R909KkBWb43GnuU+RKAbdUiztE2zTdgEAImfno= X-Received: by 2002:a9f:3241:: with SMTP id y1mr886824uad.107.1559193696177; Wed, 29 May 2019 22:21:36 -0700 (PDT) MIME-Version: 1.0 References: <1559133448-31779-1-git-send-email-dianzhangchen0@gmail.com> <20190529194852.GA23461@bombadil.infradead.org> In-Reply-To: <20190529194852.GA23461@bombadil.infradead.org> From: Dianzhang Chen Date: Thu, 30 May 2019 13:21:23 +0800 Message-ID: Subject: Re: [PATCH] mm/slab_common.c: fix possible spectre-v1 in kmalloc_slab() To: Matthew Wilcox Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-mm@kvack.org, LKML 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: thanks, i think your suggestion is ok. in my previous method is easy to understand for spectre logic, but your suggestion is more sense to use of array_index_nospec. On Thu, May 30, 2019 at 3:48 AM Matthew Wilcox wrote: > > On Wed, May 29, 2019 at 08:37:28PM +0800, Dianzhang Chen wrote: > > The `size` in kmalloc_slab() is indirectly controlled by userspace via syscall: poll(defined in fs/select.c), hence leading to a potential exploitation of the Spectre variant 1 vulnerability. > > The `size` can be controlled from: poll -> do_sys_poll -> kmalloc -> __kmalloc -> kmalloc_slab. > > > > Fix this by sanitizing `size` before using it to index size_index. > > I think it makes more sense to sanitize size in size_index_elem(), > don't you? > > static inline unsigned int size_index_elem(unsigned int bytes) > { > - return (bytes - 1) / 8; > + return array_index_nospec((bytes - 1) / 8, ARRAY_SIZE(size_index)); > } > > (untested)