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[2001:14bb:51:a4c8:5c24:24d7:ca5f:e7d2]) by smtp.gmail.com with ESMTPSA id m21sm4931849lfl.97.2018.12.21.09.42.27 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Dec 2018 09:42:28 -0800 (PST) Subject: Re: [PATCH 04/12] __wr_after_init: x86_64: __wr_op To: Andy Lutomirski Cc: Matthew Wilcox , Peter Zijlstra , Dave Hansen , Mimi Zohar , Igor Stoppa , Nadav Amit , Kees Cook , linux-integrity , Kernel Hardening , Linux-MM , LKML References: <20181219213338.26619-1-igor.stoppa@huawei.com> <20181219213338.26619-5-igor.stoppa@huawei.com> <20181220184917.GY10600@bombadil.infradead.org> From: Igor Stoppa Message-ID: <187b5db9-63e4-05c2-ddb4-004969edb4d2@gmail.com> Date: Fri, 21 Dec 2018 19:42:26 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On 21/12/2018 19:23, Andy Lutomirski wrote: > On Thu, Dec 20, 2018 at 11:19 AM Igor Stoppa wrote: >> >> >> >> On 20/12/2018 20:49, Matthew Wilcox wrote: >> >>> I think you're causing yourself more headaches by implementing this "op" >>> function. >> >> I probably misinterpreted the initial criticism on my first patchset, >> about duplication. Somehow, I'm still thinking to the endgame of having >> higher-level functions, like list management. >> >>> Here's some generic code: >> >> thank you, I have one question, below >> >>> void *wr_memcpy(void *dst, void *src, unsigned int len) >>> { >>> wr_state_t wr_state; >>> void *wr_poking_addr = __wr_addr(dst); >>> >>> local_irq_disable(); >>> wr_enable(&wr_state); >>> __wr_memcpy(wr_poking_addr, src, len); >> >> Is __wraddr() invoked inside wm_memcpy() instead of being invoked >> privately within __wr_memcpy() because the code is generic, or is there >> some other reason? >> >>> wr_disable(&wr_state); >>> local_irq_enable(); >>> >>> return dst; >>> } >>> >>> Now, x86 can define appropriate macros and functions to use the temporary_mm >>> functionality, and other architectures can do what makes sense to them. > I suspect that most architectures will want to do this exactly like > x86, though, but sure, it could be restructured like this. In spirit, I think yes, but already I couldn't find a clean ways to do multi-arch wr_enable(&wr_state), so I made that too become arch_dependent. Maybe after implementing write rare for a few archs, it becomes more clear (to me, any advice is welcome) which parts can be considered common. > On x86, I *think* that __wr_memcpy() will want to special-case len == > 1, 2, 4, and (on 64-bit) 8 byte writes to keep them atomic. i'm > guessing this is the same on most or all architectures. I switched to xxx_user() approach, as you suggested. For x86_64 I'm using copy_user() and i added a memset_user(), based on copy_user(). It's already assembly code optimized for dealing with multiples of 8-byte words or subsets. You can see this in the first patch of the patchset, even this one. I'll send out the v3 patchset in a short while. -- igor