From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 77138BD; Mon, 11 Dec 2023 07:40:03 -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 A6B83FEC; Mon, 11 Dec 2023 07:40:49 -0800 (PST) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.34.127]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B4D573F738; Mon, 11 Dec 2023 07:39:58 -0800 (PST) Date: Mon, 11 Dec 2023 15:39:56 +0000 From: Mark Rutland To: Will Deacon Cc: Robin Murphy , Joerg Roedel , Christoph Hellwig , Vineet Gupta , Russell King , Catalin Marinas , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , Paul Walmsley , Palmer Dabbelt , Albert Ou , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Suravee Suthikulpanit , David Woodhouse , Lu Baolu , Niklas Schnelle , Matthew Rosato , Gerald Schaefer , Jean-Philippe Brucker , Rob Herring , Frank Rowand , Marek Szyprowski , Jason Gunthorpe , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org, iommu@lists.linux.dev, devicetree@vger.kernel.org Subject: Re: [PATCH 3/7] ACPI/IORT: Handle memory address size limits as limits Message-ID: References: <2ae6199a9cf035c1defd42e48675b827f41cdc95.1701268753.git.robin.murphy@arm.com> <20231211132757.GE25681@willie-the-truck> <91b22090-485f-49c9-a536-849fd7f92f8e@arm.com> <20231211153023.GA26048@willie-the-truck> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231211153023.GA26048@willie-the-truck> On Mon, Dec 11, 2023 at 03:30:24PM +0000, Will Deacon wrote: > On Mon, Dec 11, 2023 at 03:01:27PM +0000, Robin Murphy wrote: > > On 2023-12-11 1:27 pm, Will Deacon wrote: > > > On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote: > > > > Return the Root Complex/Named Component memory address size limit as an > > > > inclusive limit value, rather than an exclusive size. This saves us > > > > having to special-case 64-bit overflow, and simplifies our caller too. > > > > > > > > Signed-off-by: Robin Murphy > > > > --- > > > > drivers/acpi/arm64/dma.c | 9 +++------ > > > > drivers/acpi/arm64/iort.c | 18 ++++++++---------- > > > > include/linux/acpi_iort.h | 4 ++-- > > > > 3 files changed, 13 insertions(+), 18 deletions(-) > > > > > > [...] > > > > > > > diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c > > > > index 6496ff5a6ba2..eb64d8e17dd1 100644 > > > > --- a/drivers/acpi/arm64/iort.c > > > > +++ b/drivers/acpi/arm64/iort.c > > > > @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) > > > > { return -ENODEV; } > > > > #endif > > > > -static int nc_dma_get_range(struct device *dev, u64 *size) > > > > +static int nc_dma_get_range(struct device *dev, u64 *limit) > > > > { > > > > struct acpi_iort_node *node; > > > > struct acpi_iort_named_component *ncomp; > > > > @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) > > > > return -EINVAL; > > > > } > > > > - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : > > > > - 1ULL<memory_address_limit; > > > > + *limit = (1ULL << ncomp->memory_address_limit) - 1; > > > > > > The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe > > > to drop that? You mention it in the cover letter, so clearly I'm missing > > > something! > > > > Because an unsigned shift by 64 or more generates 0 (modulo 2^64), thus > > subtracting 1 results in the correct all-bits-set value for an inclusive > > 64-bit limit. > > Oh, I'd have thought you'd have gotten one of those "left shift count >= > width of type" warnings if you did that. I think you'll get a UBSAN splat, but here the compiler doesn't know what 'ncomp->memory_address_limit' will be and so doesn't produce a compile-time warning. Regardless, it's undefined behaviour. Mark. 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 8599AC4167B for ; Mon, 11 Dec 2023 15:40:34 +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=l4823EH/FOfslXDjOh/Gzwq+r8AN6RzhjEeOP8+4xRk=; b=v5APQz994OjG3+ 2I+0v9E410S6K/V5J+mIanLaSE38u2Uo84fsvEyQO5ybf93ck19m7hQ+L4/8KHsagjrz8os+EH6MO ZNdAuHMlJPXMLvcKb8kJWV+Zg91RlFOpZ5ebClm/LaWV5ZoxcGwNH8N9WIvYixorlM1OHDdStFb5p rNOlZQjS/2KBU1yiS1p9+l4QmHveVf2rEp6lEs5RROaCpilB6PUyK5OS0bX0wtnv9HMuKFYNVMc9/ nxX/6QLnkHtJsNNipUpvBPVCgMrFBbKi+mEgswKHW/O4gj24PIQXEMy2wOPbZKUk7aeFOqb1eG35H WZ0I8w89l1Kf4izKALKg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rCiO9-005V1b-1d; Mon, 11 Dec 2023 15:40:09 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rCiO5-005UzF-1U for linux-arm-kernel@lists.infradead.org; Mon, 11 Dec 2023 15:40:07 +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 A6B83FEC; Mon, 11 Dec 2023 07:40:49 -0800 (PST) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.34.127]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B4D573F738; Mon, 11 Dec 2023 07:39:58 -0800 (PST) Date: Mon, 11 Dec 2023 15:39:56 +0000 From: Mark Rutland To: Will Deacon Cc: Robin Murphy , Joerg Roedel , Christoph Hellwig , Vineet Gupta , Russell King , Catalin Marinas , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , Paul Walmsley , Palmer Dabbelt , Albert Ou , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Suravee Suthikulpanit , David Woodhouse , Lu Baolu , Niklas Schnelle , Matthew Rosato , Gerald Schaefer , Jean-Philippe Brucker , Rob Herring , Frank Rowand , Marek Szyprowski , Jason Gunthorpe , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org, iommu@lists.linux.dev, devicetree@vger.kernel.org Subject: Re: [PATCH 3/7] ACPI/IORT: Handle memory address size limits as limits Message-ID: References: <2ae6199a9cf035c1defd42e48675b827f41cdc95.1701268753.git.robin.murphy@arm.com> <20231211132757.GE25681@willie-the-truck> <91b22090-485f-49c9-a536-849fd7f92f8e@arm.com> <20231211153023.GA26048@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20231211153023.GA26048@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231211_074005_595487_68D8DEE8 X-CRM114-Status: GOOD ( 22.66 ) 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 On Mon, Dec 11, 2023 at 03:30:24PM +0000, Will Deacon wrote: > On Mon, Dec 11, 2023 at 03:01:27PM +0000, Robin Murphy wrote: > > On 2023-12-11 1:27 pm, Will Deacon wrote: > > > On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote: > > > > Return the Root Complex/Named Component memory address size limit as an > > > > inclusive limit value, rather than an exclusive size. This saves us > > > > having to special-case 64-bit overflow, and simplifies our caller too. > > > > > > > > Signed-off-by: Robin Murphy > > > > --- > > > > drivers/acpi/arm64/dma.c | 9 +++------ > > > > drivers/acpi/arm64/iort.c | 18 ++++++++---------- > > > > include/linux/acpi_iort.h | 4 ++-- > > > > 3 files changed, 13 insertions(+), 18 deletions(-) > > > > > > [...] > > > > > > > diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c > > > > index 6496ff5a6ba2..eb64d8e17dd1 100644 > > > > --- a/drivers/acpi/arm64/iort.c > > > > +++ b/drivers/acpi/arm64/iort.c > > > > @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) > > > > { return -ENODEV; } > > > > #endif > > > > -static int nc_dma_get_range(struct device *dev, u64 *size) > > > > +static int nc_dma_get_range(struct device *dev, u64 *limit) > > > > { > > > > struct acpi_iort_node *node; > > > > struct acpi_iort_named_component *ncomp; > > > > @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) > > > > return -EINVAL; > > > > } > > > > - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : > > > > - 1ULL<memory_address_limit; > > > > + *limit = (1ULL << ncomp->memory_address_limit) - 1; > > > > > > The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe > > > to drop that? You mention it in the cover letter, so clearly I'm missing > > > something! > > > > Because an unsigned shift by 64 or more generates 0 (modulo 2^64), thus > > subtracting 1 results in the correct all-bits-set value for an inclusive > > 64-bit limit. > > Oh, I'd have thought you'd have gotten one of those "left shift count >= > width of type" warnings if you did that. I think you'll get a UBSAN splat, but here the compiler doesn't know what 'ncomp->memory_address_limit' will be and so doesn't produce a compile-time warning. Regardless, it's undefined behaviour. Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel