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Mon, 19 May 2025 07:26:36 +0000 X-OVh-ClientIp:213.192.77.249 Message-ID: Date: Mon, 19 May 2025 09:26:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Question: a module for wiping userspace RAM before shutdown/reboot/halt To: Christophe Leroy , linux-modules@vger.kernel.org, "linux-mm@kvack.org" References: Content-Language: en-US From: Danill Klimuk Autocrypt: addr=daniil.klimuk@3mdeb.com; keydata= xsFNBGSHMbYBEACgKxvpKNgbNRlo2OQHNSXhqW+eNSsAMeTkVz5omxWP/FsTcSkY+VK0S55V mQCKVlJKbX6xcBvRrIotkslqWqNQ/eYpTxUyhhTjwFTNl/XdywMBgk1qabM6uz6FPXhkT1F1 QOhtUB0BwNXu5MsQFtRST4wSjTObwZZT419PEX3RSklSOJh3jn+RcgxWzcmVQtFxBGwaeV/7 nGvQUO5TSqJvqP2AS1RzHr/GFvZY+X9kJLvtxsQP2+EqWkLWsyuNXD0NicpjETgTjKqL9iaa e7pjDDRMiaV/vl/tTsQwXhj3E2bOrZqSLynThq+Pnxnj0NYqcCWCjgCUaMH9XGv0BOCFLa0Z sl0teNUEP0+Kiwxm5TH5jPS26bxKFGn8vxczUpuorIKs5VV31/7oi3J8P7NLMEf4v+5mv0/y iBBjM94lsLG39ltF3jlHcxdgi284UC01etjA63s7H8HZlNWUiKPYR3igbfK1jqdzStWc4tzO 3++jzH19Z/96CbT1RcYWOWwxUbd+j3dNhnd+a9mTyzgxGy0254ktLtsF6EcA4yo6Iwrg9oMz 6Zy7RulQvHgA77jFdRoLscktBYmjqxvQCB09d3ciqOA6nYOK2NrBfgpUnRit2UGU8JUjfl0V bI2KK/PgHtDd7ph5sMWOqA5tyg/Lg0hmyAOQIER4MYEBvJQQWQARAQABzSdEYW5paWwgS2xp bXVrIDxkYW5paWwua2xpbXVrQDNtZGViLmNvbT7CwZcEEwEIAEEWIQSnEoFOxzDQ1VTz96RA hM4WZ2vYFgUCZIcxtgIbAwUJA8JnAAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgAAKCRBA hM4WZ2vYFshVD/wKE+W2hQp1JiAe2HmOYkO+1VGImEqYZV5uAV/jwUTO4itaeDL8LTcN/z/S Ur0EL9FgkLJ1ZsygCPXbcJUbZluQHFDg8b4Ue+UKN+ADE0R/J8BJpW9bmD4KQw3DPzk5JmTd 8h3oqHhO44nxHtNrPfG0p7B0hVDfGnLIY2ZScBl+BUedwRyS5hep0YRNMKWKlR9w1j/4mx5y X/s2ILRePI99VCUCKlPFgPvGx9I0oAOgwxhU84zXqoi8xIRSkN6F/wjV+7yKiJRfb9CmYirq MTfsY6PaiYCaTAzCmvKXjy+DuZJq/RyoLSPX2U22bzQtcKYF+CSli8RIebp0SqNoaMQZxRLQ cdw2sGgHJtbh/s0UI657PwXHw3MmK7SzeL3Bb6FsoR7RuMsQWYFWPGm/hoAmPHafPhXsowNi US852W8OWyv9OhthMFdb/OySdqt/oJTNZjWHPldYIIXFiil5byzPMz+0GEKZrZOL92HigY7a YQhH6UcjSjYIF5DjXba0K+RQYgWWd4wp48ABiaxdeSCuhzF7ioxkg/tSW7l0Ja04OMdMWPlG +VsZ3SkY9OuYeXE43VGA8gQbq43h8NJCD/y0htoFbiwjxeiSO4Lo7nuo6MYBr0mqo0GKFtNV 1i9cvMtwOw7NB1mKl2hv6rMdB5LLQ6+P4YcS0unQLLji1UFvuc7BTQRkhzG2ARAA7qEXLOKx Fr/QwDHWH5sOD75g0hdINbRphOkp88jay/fb8D52GXnllQuk8lPFL3sAvVv3wKM6lzFeD8CL ifJfVz14N7g6N8XRcPGeLZjtQCslVnjykywU7FZGSAuPaTsbc2n2CtIRa05j8jyerTQ3qLb5 aRfs6PmrjM2MCGUdPLFQcsFdcUrgp77HqjdnptWkNi/5tAaWJIvNkz7Hh13n1KXu96LMd1We JXtRQEb607HtBxZ30dMJ8qYgT8Z9S05APcXxnRZeNhBY0OJK1FWYdw7tPzsDK7ModZDTrzZu NUm4wq76AkNlvi2AehbUKKuWhnj9ztOZO6FEys9wFNa43AQhQBM7WZjScPasLvGyrJyxHPgg xDwD1r0Wc468vGVD8XySj78R4UL4gdbb1oDtVkBNLnsHDw0OchxFEk5aDDW2bFRw1RJXi+da 1QcTp8z89/LFidEvnjN8cq5HXvcabiJo2Bfyc3SZgZKw3uSqcefWZ3nd/Kt8Tmgnxn25y/kw DeQey6q6hg+FuuuKm4XED3uYvFGe9GB97+SQqpXoVjKHi8o6W2in4DW15gPwGPL4DSVgPraF smEioV280TfrNDbJG5aznmGq2IVIl4A09Ztw4adEySXXKLIDNWYesRc5Ae9TIwtpgjXKgrLi tkwvqW2Us8kmHBeOgA5z9td3qycAEQEAAcLBfAQYAQgAJhYhBKcSgU7HMNDVVPP3pECEzhZn a9gWBQJkhzG2AhsMBQkDwmcAAAoJEECEzhZna9gW+jcP/ihDd7mlmzN4pwfyjbKjDq2Kjv0C rjwAb5k9MYGOzWYQoOdvO1CXeZIxrFHGVzloXn22tcYKVY1ktm70oZ2609YkxkmWuI8+ZBev G4CETrhkWIn+UxXHzRHJ63zqrn8HFJbFzHu+Agc2vD8sKb+ekjCaBFc9jQzr9sBwMaXXnPJT olNH1zIijC3SM5guCmZ0vKwLW7+alKm/DDkPeTQJWE+kXqcixRIjEAksecOd8n1Wp71/CmsH iqo+muX+Q/WW2Kecpdq0S6GCPu3/GMtYO64Yi9+vlVJveGHmJTk1/+G8MaN+PfE6GIk8SxXL s5B3HOeSmHs0mPyTjM2524cqkoWoAPk43MH3klD8MZDrsxcFb+ef7KfODGepazrgfntQDXPu 1ijNR8wYTTn/Iv4L9Tb13DgPPknsS2GjXi/ISfqBbYgpSBdxiKseTVNMdAJ2WFHRMmIew98j g/4iKNrDqtXyPx58U/dVDVeN92qeBiQ80P6cpUa/zUih2bA0tsrrq1nnbgtZimR9zf/IeJ+p jzTpWIjcK/D0Ju9KMUYjEnhqB846cJP6i7D5fHCSDZKj14r1BDcY22lQP6wzAr2FLFoglYaR 7xMGq/UgT4ytfARCeaCJvgg6Ir9EzwURzjdLA8OA1tbFN1Z4ShfHD9VJe1Y3g9RQg3MWUZsR TIx3Est5 Organization: 3mdeb In-Reply-To: Content-Type: text/plain; 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Yes, by 'wiping' I mean 'clearing'. > Can you explain the reason this is needed? Some of our clients want to clear user space RAM during shutdown/reboot/halt sequences of Linux kernel, so the process data or any other leftovers do not leak outside current Linux kernel session (that is to firmware, or the next boot software, etc.). The reason for it to be a module that will execute in a specific moment of the sequences is to make it more predictable. I thought that if the clients want to use it, maybe it will be useful for others too :). On 5/17/25 7:25 PM, Christophe Leroy wrote: > > > Le 15/05/2025 à 15:30, Danill Klimuk a écrit : > >> Hello everyone. I have received a request to write a Linux kernel module >> that will wipe any processes leftovers from userspace RAM during/before >> Linux kernel shutdown/reboot/halt sequences. The reason I am going to do >> it inside a module is to do it in a more deterministic way that does not >> depend on any processes. AFAIK Linux kernel does not have any other >> functionalities to wipe leftovers from RAM apart from the command line >> arguments "init_on_free" and "init_on_alloc" that results in memory >> poisoning only during memory allocation and memory deallocation. These >> arguments cause the kernel to clean processes memory several times >> during runtime, that is not deterministic because of processes >> non-deterministic behavior. Hence, I want to bring the memory wiping >> mechanism in one place and make it more deterministic. The question is: >> >> Maybe the Linux kernel already have such functionalities implemented? > > Linux memory management topics should be sent to linux-mm@kvack.org > >> >> Currently I am planning to implement the wiping process to be triggered >> by "reboot_notifier_callback", so to wipe RAM after PID 1 process >> finishes and no other processes are executing. I am looking forward to >> merging the module into Linux kernel upstream too. > > What do you mean by 'wiping', do you mean 'clearing' ? > > Can you explain the reason this is needed ? > > Christophe > > -- Best regards, Daniil. 3mdeb Zarhus team leader.