Date: Thu, 17 Aug 2017 17:44:29 -0400 From: Theodore Ts'o <tytso@....edu> To: Daniel Micay <danielmicay@...il.com> Cc: Laura Abbott <labbott@...hat.com>, Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCHv3 2/2] extract early boot entropy from the passed cmdline On Thu, Aug 17, 2017 at 04:57:07PM -0400, Daniel Micay wrote: > > I did say 'external attacker' but it could be made clearer. > > Er, s/say/mean to imply/ Right, that's why I had suggested modifying the first few lines of the commit description to read something like this: Feed the boot command-line as to the /dev/random entropy pool Existing Android bootloaders usually pass data which may not be known by an external attacker on the kernel command-line. It may also be the case on other embedded systems. Sample command-line from a Google Pixel running CopperheadOS: (Or something like that.) > I'll look into having the kernel stash some entropy in pstore soon since > that seems like it could be a great improvement. I'm not sure how often > / where it should hook into for regularly refreshing it though. Doing it > only on powering down isn't ideal. One thing we could do is to agree on a standard place where the entropy would be stashed, and then have the kernel remove it from being visible in /proc/cmdline. That's not a perfect answer, since the user might be able to look at the command line via other mechanisms. (For example, on x86, by looking at GRUB while the system is booting.) However, an attacker who is merely running code on the local system is not likely to be gain access to that value --- so it's definitely an improvement. Refreshing the entry immediately after boot, and before a clean shutdown would be ideal from a security perspective. I don't know if there are write endurance issues with updating the pstore that frequently, though. - Ted
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.