Messages in this thread | | | Subject | Re: [PATCHv4 2/2] mm/page_poisoning.c: Allow for zero poisoning | From | Laura Abbott <> | Date | Mon, 7 Mar 2016 16:33:00 -0800 |
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On 03/04/2016 04:07 PM, Andrew Morton wrote: > On Fri, 4 Mar 2016 15:50:48 -0800 Laura Abbott <labbott@fedoraproject.org> 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
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