On 10/10/2017 01:51, Tobin C. Harding wrote: > On Mon, Oct 09, 2017 at 12:58:12PM +0200, Paolo Bonzini wrote: >> On 09/10/2017 12:04, Tobin C. Harding wrote: >>> On Mon, Oct 09, 2017 at 03:49:38AM -0400, Paolo Bonzini wrote: >>>> >>>> >>>> ----- Original Message ----- >>>>> From: "Tobin C. Harding" <me@xxxxxxxx> >>>>> To: "Paolo Bonzini" <pbonzini@xxxxxxxxxx>, rkrcmar@xxxxxxxxxx >>>>> Cc: kvm@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, "Tobin C. Harding" <me@xxxxxxxx> >>>>> Sent: Monday, October 9, 2017 8:30:14 AM >>>>> Subject: [PATCH] KVM: remove printing of token address >>>>> >>>>> KVM currently prints the address of the consumer token. It is not >>>>> immediately clear what benefit it is to see this address. Printing >>>>> this address leaks kernel pointers into dmesg and is a security risk. >>>>> >>>>> Remove the consumer token address from error message output. >>>> >>>> It should use %pK instead. >>> >>> Is there any other way we can identify a token? There is some push back against kpt_restrict (as >>> used by %pK) at the moment. If there is another sane way to do it perhaps we could consider that, >>> else I'll use %pK for v2. >> >> Not really, we know it is an eventfd but you can't go from the struct >> eventfd_ctx* (the token) to the corresponding struct file. >> >> I'm not sure about the pushback... I've read your name in >> https://lwn.net/Articles/735589/ :) and that article says "the same >> effect as a restrictive kptr_restrict setting could be achieved by >> searching for (and fixing) every use of unadorned "%p" directives in the >> kernel". As I understand it, the push back is against restrictive >> kptr_restrict settings, not against using "%pK" _to avoid the need_ for >> such a restrictive setting. > > In the thread that article is based on Linus airs his view that kptr_restrict is fundamentally > broken. And I agree with him that more restrictive kptr_restrict settings are kind of broken, because either no one would use them, or if you made them the default people would start using "%x". Further there is the issue that people are _already_ using "%x" already instead of e.g. "%pa". So yeah, kptr_restrict does look a bit like security theater. However, issues with kptr_restrict do not necessarily extend to "%pK" or "%pa". The problem is that there are too many instances of "%p", and I'm happy that you want to fix them. Since we _do_ have kptr_restrict, I don't see anything wrong with converting them to "%pK". And if everybody started using "%pK" and "%pa" appropriately, then 1) you wouldn't need restrictive kptr_restrict settings anymore; 2) kptr_restrict would actually prevent address leaks. > Would you be happy if instead of printing the pointer we printed a unique identifier (some suitable > hash of the pointer value)? As long as the "suitable hash" is computed inside printk, I don't care. If the suitable hash would be in KVM or VFIO code, then please no. :) Paolo > I'm working on that patch ATM, if this sounds ok I'll leave this patch > until unique identifiers are implemented. > > But if we really want the address here I can put in the patch using %pK. What is your thoughts? > >> Thanks, >> >> Paolo >> >>>> Also, please do the same change on the VFIO >>>> side (drivers/vfio/pci/vfio_pci_intrs.c, call to irq_bypass_register_producer). > > And same here obviously. > > thanks, > Tobin. >
