On Mon, 24 Feb 2014, H. Peter Anvin wrote: > On February 24, 2014 8:34:30 AM PST, Vince Weaver <vincent.wea...@maine.edu> > wrote: > >On Mon, 24 Feb 2014, Vince Weaver wrote: > > > >> Just touching the mmap page with a write of a single byte (it doesn't > > > >> matter where) is enough to trigger the bug. > > > >OK, investigating this more. > > > >perf_fuzzer-2971 [000] 154.944114: page_fault_user: > >address=0xf7729000 ip=0x41efab error_code=0x6 > >perf_fuzzer-2971 [000] 154.944118: function: > >ip=0xffffffff810d40e7 parent_ip=0xffffffff810d0840 > >perf_fuzzer-2971 [000] 154.944119: function: > >ip=0xffffffff812a91a5 parent_ip=0xffffffff81013ff5 > >perf_fuzzer-2971 [000] 154.944120: function: > >ip=0xffffffff8153837c parent_ip=0xffffffff81535432 > >perf_fuzzer-2971 [000] 154.944121: page_fault_kernel: > >address=0x22e0 ip=0xffffffff812a7d5c error_code=0x0
> Ok, so the obvious question is what is at that kernel address? > It's in copy_user_generic_string() rep movsq %ds:(%rsi),%es:(%rdi) And looking at the ftrace: perf_fuzzer-2979 [000] 161.475920: page_fault_user: address=__per_cpu_end ip=__per_cpu_end error_code=0x6 perf_fuzzer-2979 [000] 161.475922: function: perf_callchain perf_fuzzer-2979 [000] 161.475922: function: copy_from_user_nmi perf_fuzzer-2979 [000] 161.475923: function: trace_do_page_fault perf_fuzzer-2979 [000] 161.475924: page_fault_kernel: address=irq_stack_union ip=copy_user_generic_string error_code=0x0 What is likely happening is the user page fault is triggering code to do a "perf_callchain" dump, which is calling copy_from_user_nmi() which calls copy_user_generic_string() which is somehow getting the user RBP in the RDI register somehow? Vince -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/