From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com References: <1457135448-15541-1-git-send-email-labbott@fedoraproject.org> <1457135448-15541-3-git-send-email-labbott@fedoraproject.org> <20160304160751.05931d89f451626b58073489@linux-foundation.org> From: Laura Abbott Message-ID: <56DE1DBC.5050403@redhat.com> Date: Mon, 7 Mar 2016 16:33:00 -0800 MIME-Version: 1.0 In-Reply-To: <20160304160751.05931d89f451626b58073489@linux-foundation.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: [kernel-hardening] Re: [PATCHv4 2/2] mm/page_poisoning.c: Allow for zero poisoning To: Andrew Morton , Laura Abbott Cc: "Kirill A. Shutemov" , Vlastimil Babka , Michal Hocko , Kees Cook , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com List-ID: On 03/04/2016 04:07 PM, Andrew Morton wrote: > On Fri, 4 Mar 2016 15:50:48 -0800 Laura Abbott wrote: > >> >> By default, page poisoning uses a poison value (0xaa) on free. If this >> is changed to 0, the page is not only sanitized but zeroing on alloc >> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting >> corruption from the poisoning is harder to detect. This feature also >> cannot be used with hibernation since pages are not guaranteed to be >> zeroed after hibernation. >> >> Credit to Grsecurity/PaX team for inspiring this work >> >> --- a/kernel/power/hibernate.c >> +++ b/kernel/power/hibernate.c >> @@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str) >> return nohibernate_setup(str); >> } >> >> +static int __init page_poison_nohibernate_setup(char *str) >> +{ >> +#ifdef CONFIG_PAGE_POISONING_ZERO >> + /* >> + * The zeroing option for page poison skips the checks on alloc. >> + * since hibernation doesn't save free pages there's no way to >> + * guarantee the pages will still be zeroed. >> + */ >> + if (!strcmp(str, "on")) { >> + pr_info("Disabling hibernation due to page poisoning\n"); >> + return nohibernate_setup(str); >> + } >> +#endif >> + return 1; >> +} > > It seems a bit unfriendly to silently accept the boot option but not > actually do anything with it. Perhaps a `#else pr_info("sorry")' is > needed. > > But I bet we made the same mistake in 1000 other places. > > What happens if page_poison_nohibernate_setup() simply doesn't exist > when CONFIG_PAGE_POISONING_ZERO=n? It looks like > kernel/params.c:parse_args() says "Unknown parameter". > > I didn't see that behavior when I tested, even with nonsense parameters. It looks like it might fall back to some other behavior before giving -ENOENT? It's also worth noting the page_poison= option is also parsed in mm/page_poison.c to do other on/off of the poisoning feature. The option code supported it and it seemed to match better with what the existing hibernate code was doing with turning off options. Thanks, Laura