On Wed, Aug 24, 2016 at 02:37:07PM -0500, Josh Poimboeuf wrote: > On Wed, Aug 24, 2016 at 02:37:21PM -0400, Linus Torvalds wrote: > > On Wed, Aug 24, 2016 at 2:22 PM, Peter Zijlstra <pet...@infradead.org> > > wrote: > > > > > > I actively disable KASLR on my dev box and feed these hex numbers into > > > addr2line -ie vmlinux to find where in the function we are. > > > > > > Having the option to make %pB generate them works for me. > > > > Yeah, considering that this is the only place this is used, changing > > %pB sounds quite reasonable. > > There's now another use of '%pB' in proc_pid_stack() in the tip tree: I > changed it to '%pB' from '%pS'. But I think the modified '%pB' would > work there as well. > > > We could perhaps make %pB show the hex numbers and address (so pB > > would expand to "[<hex>] symbolname".if > > > > (a) not randomizing (so the hex numbers _may_ be useful) > > > > (b) kptr_restrict is 0 (so the hex numbers are "safe" in the dmesg) > > > > and fall back to just the symbolic name if either of those aren't true? > > Do we really need to check for both? '%pK' only checks kptr_restrict. > I'd think we should be consistent with that. And maybe there are some > scenarios where the actual text addresses provide useful debug > information if KASLR is enabled and kptr_restrict is zero.
So I was looking at implementing this, and I noticed that '%pK' prints "pK-error" if it's called from interrupt context when kptr_restrict==1. Because checking CAP_SYSLOG would be meaningless in that case. I don't really understand the point of the "pK-error" thing. Any reason why we can't print zero, i.e., just degrade the kptr_restrict from 1 to 2 in an interrupt? That would make the '%pK' code simpler and usable from interrupt context. Also it would make its behavior consistent with the proposed '%pB' changes, and the kptr_restrict code could be shared between '%pK' and '%pB'. Kess (or others), any objections if I make that change? -- Josh
