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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2E685C54EAA for ; Fri, 27 Jan 2023 15:15:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=C82R8uoQGg001YzxfjMIlVw/7p9V4bMWB7dphKIaJs4=; b=PQkf1nScUkR7el GrulChwT9UynkGqSxKD+DWVsUmlMzP/uuxzTuJhGLOazoBTugTNy5DrMABBYcbP9Pnl+HUrHF5d0V EcdcXWftDOl3T7nfNbK06sNyGnboBM2zqeUzjDDEZmBtpbPZyqQOXayUcg/JZifFRMr1eDbpoteFC mIvBn1t7R097TIRap+us8jI6DfV4sqHXdGvIpAPuWnHPt4BkCH+QPeCR6N7v3eqDxQf3FA1D0VjLI JqsDSem0scCd1f68zsW25ZWKfiBKJQoOlGGgSmxItmiPWfI8fEFlZx1P25qh0gUl1iFvc3ZGh6VfO Z80JeMGqacFTfZBFdhKg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pLQQt-00FQYG-Bv; Fri, 27 Jan 2023 15:14:27 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pLQQn-00FQWU-Fz for linux-arm-kernel@lists.infradead.org; Fri, 27 Jan 2023 15:14:24 +0000 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 E33752B; Fri, 27 Jan 2023 07:14:58 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.48.236]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DA2783F64C; Fri, 27 Jan 2023 07:14:15 -0800 (PST) Date: Fri, 27 Jan 2023 15:14:05 +0000 From: Mark Rutland To: Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, will@kernel.org, catalin.marinas@arm.com, Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] arm64/mm: Intercept pfn changes in set_pte_at() Message-ID: References: <20230109052816.405335-1-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230109052816.405335-1-anshuman.khandual@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230127_071421_652863_512C3B94 X-CRM114-Status: GOOD ( 28.25 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Annshuman, On Mon, Jan 09, 2023 at 10:58:16AM +0530, Anshuman Khandual wrote: > Changing pfn on a user page table mapped entry, without first going through > break-before-make (BBM) procedure is unsafe. This just updates set_pte_at() > to intercept such changes, via an updated pgattr_change_is_safe(). This new > check happens via __check_racy_pte_update(), which has now been renamed as > __check_safe_pte_update(). > > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Mark Rutland > Cc: Andrew Morton > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual > --- > This applies on v6.2-rc3. This patch had some test time on an internal CI > system without any issues being reported. Can you elaborate on this a little bit? It's not entirely clear what that internal CI system has tested. It would be helpful if you could indicate: * What sort of testing has been done by the CI system? e.g. is this just booting, running LTP, something else? * Has this tried a bunch of configurations and/or machines? * If any targetted stress tests have been used? e.g. stress-ng's memory system tests? I'm assuming that's hitting LTP on a few machines/configs, which'd be reasonable. It'd just be nice to confirm exactly what has been tested. I've added this to my lcoal syzkaller instance's test branch, and I'll shout if that hits anything over the weekend. > Changes in V1: > > https://lore.kernel.org/all/20221116031001.292236-1-anshuman.khandual@arm.com/ Did you mean to list some cahnges here? > > arch/arm64/include/asm/pgtable.h | 8 ++++++-- > arch/arm64/mm/mmu.c | 8 +++++++- > 2 files changed, 13 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index b4bbeed80fb6..832c9c8fb58f 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -275,6 +275,7 @@ static inline void set_pte(pte_t *ptep, pte_t pte) > } > > extern void __sync_icache_dcache(pte_t pteval); > +bool pgattr_change_is_safe(u64 old, u64 new); > > /* > * PTE bits configuration in the presence of hardware Dirty Bit Management > @@ -292,7 +293,7 @@ extern void __sync_icache_dcache(pte_t pteval); > * PTE_DIRTY || (PTE_WRITE && !PTE_RDONLY) > */ > > -static inline void __check_racy_pte_update(struct mm_struct *mm, pte_t *ptep, > +static inline void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep, > pte_t pte) > { > pte_t old_pte; > @@ -318,6 +319,9 @@ static inline void __check_racy_pte_update(struct mm_struct *mm, pte_t *ptep, > VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte), > "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx", > __func__, pte_val(old_pte), pte_val(pte)); > + VM_WARN_ONCE(!pgattr_change_is_safe(pte_val(old_pte), pte_val(pte)), > + "%s: unsafe attribute change: 0x%016llx -> 0x%016llx", > + __func__, pte_val(old_pte), pte_val(pte)); > } > > static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr, > @@ -346,7 +350,7 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr, > mte_sync_tags(old_pte, pte); > } > > - __check_racy_pte_update(mm, ptep, pte); > + __check_safe_pte_update(mm, ptep, pte); > > set_pte(ptep, pte); > } > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 14c87e8d69d8..a1d16b35c4f6 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -133,7 +133,7 @@ static phys_addr_t __init early_pgtable_alloc(int shift) > return phys; > } > > -static bool pgattr_change_is_safe(u64 old, u64 new) > +bool pgattr_change_is_safe(u64 old, u64 new) > { > /* > * The following mapping attributes may be updated in live > @@ -145,6 +145,12 @@ static bool pgattr_change_is_safe(u64 old, u64 new) > if (old == 0 || new == 0) > return true; These checks above should really use pte_valid(); we were just being lazy when this was originally written since for the init_*() cases the memory should be zero initially. So could you make that: if (!pte_valid(__pte(old)) || !pte_valid(__pte(new))) return true; > + /* If old and new ptes are valid, pfn should not change */ > + if (pte_valid(__pte(old)) && pte_valid(__pte(new))) { > + if (pte_pfn(__pte(old)) != pte_pfn(__pte(new))) > + return false; > + } With the above change, it's clear that both must be valid to get this far, and this check can be reduced to: /* A live entry's pfn should not change */ if (pte_pfn(__pte(old)) != pte_pfn(__pte(new))) return false; With those changes: Acked-by: Mark Rutland Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel