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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2740DC64ED6 for ; Tue, 28 Feb 2023 11:02:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230459AbjB1LCC (ORCPT ); Tue, 28 Feb 2023 06:02:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52328 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230303AbjB1LCC (ORCPT ); Tue, 28 Feb 2023 06:02:02 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 265A625B85 for ; Tue, 28 Feb 2023 03:02:00 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B2E93C14; Tue, 28 Feb 2023 03:02:43 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.17.252]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 49DF53F881; Tue, 28 Feb 2023 03:01:59 -0800 (PST) Date: Tue, 28 Feb 2023 11:01:56 +0000 From: Mark Rutland To: Ard Biesheuvel Cc: linux-arm-kernel@lists.infradead.org, linux-efi@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, maz@kernel.org, broonie@kernel.org Subject: Re: [PATCH] arm64: kaslr: don't pretend KASLR is enabled if offset < MIN_KIMG_ALIGN Message-ID: References: <20230223204101.1500373-1-ardb@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230223204101.1500373-1-ardb@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org On Thu, Feb 23, 2023 at 09:41:01PM +0100, Ard Biesheuvel wrote: > Our virtual KASLR displacement is a randomly chosen multiple of > 2 MiB plus an offset that is equal to the physical placement modulo 2 > MiB. This arrangement ensures that we can always use 2 MiB block > mappings (or contiguous PTE mappings for 16k or 64k pages) to map the > kernel. > > This means that a KASLR offset of less than 2 MiB is simply the product > of this physical displacement, and no randomization has actually taken > place. Currently, we use 'kaslr_offset() > 0' to decide whether or not > randomization has occurred, and so we misidentify this case. > Fix this, by correctly identifying the case where the virtual > displacement is a result of the physical displacement only. > > Signed-off-by: Ard Biesheuvel Acked-by: Mark Rutland Mark. > --- > I have sent out the same patch with a much shorter commit log as part of > my LPA2 series before, but I only realized today that this is likely to > fix most occurrences of the issue where a single 10g vmalloc() call > break subsequent module loading, so I am reposting it in isolation. > > arch/arm64/include/asm/memory.h | 11 +++++++++++ > arch/arm64/kernel/cpufeature.c | 2 +- > arch/arm64/kernel/kaslr.c | 2 +- > 3 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index 9dd08cd339c3f028..78e5163836a0ab95 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -180,6 +180,7 @@ > #include > #include > #include > +#include > #include > > #if VA_BITS > 48 > @@ -203,6 +204,16 @@ static inline unsigned long kaslr_offset(void) > return kimage_vaddr - KIMAGE_VADDR; > } > > +static inline bool kaslr_enabled(void) > +{ > + /* > + * The KASLR offset modulo MIN_KIMG_ALIGN is taken from the physical > + * placement of the image rather than from the seed, so a displacement > + * of less than MIN_KIMG_ALIGN means that no seed was provided. > + */ > + return kaslr_offset() >= MIN_KIMG_ALIGN; > +} > + > /* > * Allow all memory at the discovery stage. We will clip it later. > */ > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 45a42cf2191c36c3..5643a9ca502af207 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1633,7 +1633,7 @@ bool kaslr_requires_kpti(void) > return false; > } > > - return kaslr_offset() > 0; > + return kaslr_enabled(); > } > > static bool __meltdown_safe = true; > diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c > index 325455d16dbcb31a..e7477f21a4c9d062 100644 > --- a/arch/arm64/kernel/kaslr.c > +++ b/arch/arm64/kernel/kaslr.c > @@ -41,7 +41,7 @@ static int __init kaslr_init(void) > return 0; > } > > - if (!kaslr_offset()) { > + if (!kaslr_enabled()) { > pr_warn("KASLR disabled due to lack of seed\n"); > return 0; > } > -- > 2.39.1 >