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Mon, 20 Jul 2020 22:15:38 -0700 (PDT) Subject: Re: [PATCH 1/6] syscalls: use uaccess_kernel in addr_limit_user_check To: Christoph Hellwig Cc: Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Andrew Morton , Linus Torvalds , linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200714105505.935079-1-hch@lst.de> <20200714105505.935079-2-hch@lst.de> <20200718013849.GA157764@roeck-us.net> <20200718094846.GA8593@lst.de> <20200720221046.GA86726@roeck-us.net> <20200721045834.GA9613@lst.de> From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= Message-ID: Date: Mon, 20 Jul 2020 22:15:37 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200721045834.GA9613@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/20/20 9:58 PM, Christoph Hellwig wrote: > On Mon, Jul 20, 2020 at 03:10:46PM -0700, Guenter Roeck wrote: >> I had another look into the code. Right after this patch, I see >> >> #define uaccess_kernel() segment_eq(get_fs(), KERNEL_DS) >> >> Yet, this patch is: >> >> - if (CHECK_DATA_CORRUPTION(!segment_eq(get_fs(), USER_DS), >> + if (CHECK_DATA_CORRUPTION(uaccess_kernel(), >> >> So there is a negation in the condition. Indeed, the following change >> on top of next-20200720 fixes the problem for mps2-an385. >> >> - if (CHECK_DATA_CORRUPTION(uaccess_kernel(), >> + if (CHECK_DATA_CORRUPTION(!uaccess_kernel(), >> >> How does this work anywhere ? > > No, that is the wrong check - we want to make sure the address > space override doesn't leak to userspace. The problem is that > armnommu (and m68knommu, but that doesn't call the offending > function) pretends to not have a kernel address space, which doesn't > really work. Here is the fix I sent out yesterday, which I should > have Cc'ed you on, sorry: > The patch below makes sense, and it does work, but I still suspect that something with your original patch is wrong, or at least suspicious. Reason: My change above (Adding the "!") works for _all_ of my arm boot tests. Or, in other words, it doesn't make a difference if true or false is passed as first parameter of CHECK_DATA_CORRUPTION(), except for nommu systems. Also, unless I am really missing something, your original patch _does_ reverse the logic. I didn't track this down further. Thanks, Guenter > --- >>>From 2bb889b2d99a2d978e90640ade8fe02359287092 Mon Sep 17 00:00:00 2001 > From: Christoph Hellwig > Date: Mon, 20 Jul 2020 17:46:50 +0200 > Subject: arm: don't call addr_limit_user_check for nommu > > On arm nommu kernel use the same constant for USER_DS and KERNEL_DS, > and seqment_eq always returns false. With the current check in > addr_limit_user_check that works by accident, but when replacing > seqment_eq with uaccess_kerne it will fail. Just remove the not > needed check entirely. > > Signed-off-by: Christoph Hellwig > Reported-by: Guenter Roeck Tested-by: Guenter Roeck > --- > arch/arm/kernel/signal.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c > index ab2568996ddb0c..c9dc912b83f012 100644 > --- a/arch/arm/kernel/signal.c > +++ b/arch/arm/kernel/signal.c > @@ -713,7 +713,9 @@ struct page *get_signal_page(void) > /* Defer to generic check */ > asmlinkage void addr_limit_check_failed(void) > { > +#ifdef CONFIG_MMU > addr_limit_user_check(); > +#endif > } > > #ifdef CONFIG_DEBUG_RSEQ >