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[209.85.220.65]) by mx.google.com with SMTPS id g7sor87820vsk.57.2019.05.29.09.40.06 for (Google Transport Security); Wed, 29 May 2019 09:40:06 -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=gy54YSWi; 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=+Esfl3nvaEBw2uCWEGOwNd1KcpJR7qnstyVJ5GKtC10=; b=gy54YSWi28xfcPumIcxdQBpxiv38UYPyQki2rU5FibosdeZ6MlUtt9mGYX3pMzpi1J eVhOA5uX5C/8oMK59ewu0GTbMw/NJWIUQ8b/ZIBDbt98ekfp++OMeCkgUOCvHQqDoN8q DaT+H9TyYWJTCERqolLABJA2fLCqFKB1pboH6qY+GtugTcyXA1u2hJOOP4KVS5o8T1W0 Nc3mxPD+goAx+22GUHKIz3rE9eBxPxsWhYqcyXvXu+t7PAS8w0XKOkNJlFUXgc+fItQU niid+sGwkxSgn5eDnRpH3eTcty2oJDRMsOtoLpYvHkC93a4vKqdqfiIJhAnbRHUedyz6 NvjA== X-Google-Smtp-Source: APXvYqwhVWfGociEat3pJKeWFTfSJFNJ89kc9w5M4Opt5Pu3UHJ1E0/+S9NVwIgBcTxJaDoqMh03meYLgWch4Id81Lc= X-Received: by 2002:a67:ea58:: with SMTP id r24mr5616881vso.60.1559148004894; Wed, 29 May 2019 09:40:04 -0700 (PDT) MIME-Version: 1.0 References: <1559133448-31779-1-git-send-email-dianzhangchen0@gmail.com> <20190529162532.GG18589@dhcp22.suse.cz> In-Reply-To: <20190529162532.GG18589@dhcp22.suse.cz> From: Dianzhang Chen Date: Thu, 30 May 2019 00:39:53 +0800 Message-ID: Subject: Re: [PATCH] mm/slab_common.c: fix possible spectre-v1 in kmalloc_slab() To: Michal Hocko 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: It's come from `192+1`. The more code fragment is: if (size <= 192) { if (!size) return ZERO_SIZE_PTR; size = array_index_nospec(size, 193); index = size_index[size_index_elem(size)]; } Sine array_index_nospec(index, size) can clamp the index within the range of [0, size), so in order to make the `size<=192`, need to clamp the index in the range of [0, 192+1) . On Thu, May 30, 2019 at 12:25 AM Michal Hocko wrote: > > On Wed 29-05-19 20:37:28, Dianzhang Chen wrote: > [...] > > @@ -1056,6 +1057,7 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags) > > if (!size) > > return ZERO_SIZE_PTR; > > > > + size = array_index_nospec(size, 193); > > index = size_index[size_index_elem(size)]; > > What is this 193 magic number? > -- > Michal Hocko > SUSE Labs