On Thu, 13 Mar 2014 15:59:24 +0000 Matthew Garrett <matthew.garrett@xxxxxxxxxx> wrote: > On Thu, 2014-03-13 at 20:33 +1100, James Morris wrote: > > > I'll take it, but there's unanswered review feedback (your response to the > > first question), and Alan raised some doubts about the patches which I'm > > not sure have been resolved. > > The remaining opens seem to be CAP_SYS_RAWIO and firmware signing? > Ironically, disabling CAP_SYS_RAWIO disables firmware loading… > > The problem with CAP_SYS_RAWIO is that its semantics were never > sufficiently well documented, and as a result it's a mixture of "This is > incredibly dangerous" and "We replaced a check for uid 0 with whichever > capability seemed to have the most appropriate name". I've gone through > all the uses of CAP_SYS_RAWIO and added additional checks to the generic > ones that seem appropriate. There's a couple of old drivers that use it > to gate access to features that potentially allow arbitrary DMA and it > might be worth cleaning those up, but the only general case I haven't > modified is the ability to send arbitrary SCSI commands from userspace. > My understanding is that endpoints aren't going to be able to DMA to > arbitrary addresses, so that doesn't seem like a problem. > > On the other hand, disabling CAP_SYS_RAWIO *definitely* breaks expected > functionality - firmware loading and the fibmap ioctl are probably the > most obvious. And changing the use of CAP_SYS_RAWIO potentially breaks > userspace expectations, so we're kind of stuck there. If I have CAP_SYS_RAWIO I can make arbitary ring 0 calls from userspace, trivially and in a fashion well known and documented. So if that isn't sufficient then we need to sort CAP_foo out first. You've missed a few others too - mem= (especially with exactmap) for example. Alan -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
