On Mon, Feb 24, 2014 at 12:10:44PM -0500, Vince Weaver wrote: > 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?
So that code very much relies on the 'recursive' NMI/iret magic from Steve, patch 3f3c8b8c4b2a3 (and assorted fixes later). If CR2 is getting corrupted; 7fbb98c5cb075 seems relevant. Peter, does x32 have a slightly different ABI/calling convention that would make any of these patches just slightly 'off'? -- 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/
