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Thu, 23 May 2019 21:49:13 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x4NLmFZJ185512; Thu, 23 May 2019 21:49:12 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userp3020.oracle.com with ESMTP id 2smsgvrm93-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 23 May 2019 21:49:12 +0000 Received: from abhmp0002.oracle.com (abhmp0002.oracle.com [141.146.116.8]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x4NLn8SI003595; Thu, 23 May 2019 21:49:09 GMT Received: from [192.168.1.16] (/24.9.64.241) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 23 May 2019 21:49:08 +0000 Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel To: Catalin Marinas References: <20190517144931.GA56186@arrakis.emea.arm.com> <20190521182932.sm4vxweuwo5ermyd@mbp> <201905211633.6C0BF0C2@keescook> <6049844a-65f5-f513-5b58-7141588fef2b@oracle.com> <20190523201105.oifkksus4rzcwqt4@mbp> From: Khalid Aziz Organization: Oracle Corp Message-ID: Date: Thu, 23 May 2019 15:49:05 -0600 User-Agent: Mozilla/5.0 (X11; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 5/23/19 2:11 PM, Catalin Marinas wrote: > Hi Khalid, > > On Thu, May 23, 2019 at 11:51:40AM -0600, Khalid Aziz wrote: >> On 5/21/19 6:04 PM, Kees Cook wrote: >>> As an aside: I think Sparc ADI support in Linux actually side-stepped >>> this[1] (i.e. chose "solution 1"): "All addresses passed to kernel must >>> be non-ADI tagged addresses." (And sadly, "Kernel does not enable ADI >>> for kernel code.") I think this was a mistake we should not repeat for >>> arm64 (we do seem to be at least in agreement about this, I think). >>> >>> [1] https://lore.kernel.org/patchwork/patch/654481/ >> >> That is a very early version of the sparc ADI patch. Support for tagged >> addresses in syscalls was added in later versions and is in the patch >> that is in the kernel. > > I tried to figure out but I'm not familiar with the sparc port. How did > you solve the tagged address going into various syscall implementations > in the kernel (e.g. sys_write)? Is the tag removed on kernel entry or it > ends up deeper in the core code? > Another spot I should point out in ADI patch - Tags are not stored in VMAs and IOMMU does not support ADI tags on M7. ADI tags are stripped before userspace addresses are passed to IOMMU in the following snippet from the patch: diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c index 5335ba3c850e..357b6047653a 100644 --- a/arch/sparc/mm/gup.c +++ b/arch/sparc/mm/gup.c @@ -201,6 +202,24 @@ int __get_user_pages_fast(unsigned long start, int nr_pages , int write, pgd_t *pgdp; int nr = 0; +#ifdef CONFIG_SPARC64 + if (adi_capable()) { + long addr = start; + + /* If userspace has passed a versioned address, kernel + * will not find it in the VMAs since it does not store + * the version tags in the list of VMAs. Storing version + * tags in list of VMAs is impractical since they can be + * changed any time from userspace without dropping into + * kernel. Any address search in VMAs will be done with + * non-versioned addresses. Ensure the ADI version bits + * are dropped here by sign extending the last bit before + * ADI bits. IOMMU does not implement version tags. + */ + addr = (addr << (long)adi_nbits()) >> (long)adi_nbits(); + start = addr; + } +#endif start &= PAGE_MASK; addr = start; len = (unsigned long) nr_pages << PAGE_SHIFT; -- Khalid _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel