From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1D177C54FD0 for ; Fri, 24 Apr 2020 13:07:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0A9020736 for ; Fri, 24 Apr 2020 13:07:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587733621; bh=u/xP6CoK1MUmVKKpWlYTdz2lShxhmNKAh4XSY+FwLjI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=V+MZXtJNCtE2JAd8o7nlLmwMIcwlw8Ko6EuyS6oovHmdJevLCfWl9lRpQoxmQq/SJ LxaDNZSDgbZ63R4mfBjq4akYz0rRNM2X//ZKlUZm6INVm+jQElNFzdM1MKYe8iAnpc uOYHcE5EzRX72Xld9Gndgad6ObafqqMOkpTUJMhk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728193AbgDXNHA (ORCPT ); Fri, 24 Apr 2020 09:07:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:57592 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728124AbgDXNG4 (ORCPT ); Fri, 24 Apr 2020 09:06:56 -0400 Received: from e123331-lin.home (amontpellier-657-1-18-247.w109-210.abo.wanadoo.fr [109.210.65.247]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E50ED20728; Fri, 24 Apr 2020 13:06:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587733615; bh=u/xP6CoK1MUmVKKpWlYTdz2lShxhmNKAh4XSY+FwLjI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ej66MkSHbWOonlumdQ9GGnTn+UsiBagZBTkYO+Jv5zmh/HazYXl0bZV4rkQqIoVYE 2Zq5Wa+A8Lo66KcR8sJF+lDLkNmALZBcBSP9Tk6oBNaJ3p3v/y6lVTUmKy4RuZyuUQ IGI9ILrieHZ3fH6Y+0ISv4vHQ282P9wI5Wf3O8D8= From: Ard Biesheuvel To: linux-efi@vger.kernel.org, Ingo Molnar , Thomas Gleixner Cc: Ard Biesheuvel , linux-kernel@vger.kernel.org, Arvind Sankar , Atish Patra , Palmer Dabbelt , Zou Wei Subject: [PATCH 20/33] efi/libstub/random: Increase random alloc granularity Date: Fri, 24 Apr 2020 15:05:18 +0200 Message-Id: <20200424130531.30518-21-ardb@kernel.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200424130531.30518-1-ardb@kernel.org> References: <20200424130531.30518-1-ardb@kernel.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The implementation of efi_random_alloc() arbitrarily truncates the provided random seed to 16 bits, which limits the granularity of the randomly chosen allocation offset in memory. This is currently only an issue if the size of physical memory exceeds 128 GB, but going forward, we will reduce the allocation alignment to 64 KB, and this means we need to increase the granularity to ensure that the random memory allocations are distributed evenly. We will need to switch to 64-bit arithmetic for the multiplication, but this does not result in 64-bit integer intrinsic calls on ARM or on i386. Signed-off-by: Ard Biesheuvel --- drivers/firmware/efi/libstub/randomalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/firmware/efi/libstub/randomalloc.c b/drivers/firmware/efi/libstub/randomalloc.c index 6200dfa650f5..a408df474d83 100644 --- a/drivers/firmware/efi/libstub/randomalloc.c +++ b/drivers/firmware/efi/libstub/randomalloc.c @@ -87,7 +87,7 @@ efi_status_t efi_random_alloc(unsigned long size, } /* find a random number between 0 and total_slots */ - target_slot = (total_slots * (u16)random_seed) >> 16; + target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32; /* * target_slot is now a value in the range [0, total_slots), and so -- 2.17.1