On 10/01/2013 10:43 PM, Tejun Heo wrote: > Hello, > > On Tue, Oct 01, 2013 at 10:35:20PM +0200, Helge Deller wrote: >> print_worker_info() includes no validity check on the pwq and wq >> pointers before handing them over to the probe_kernel_read() functions. >> >> It seems that most architectures don't care about that, but at least on >> the parisc architecture this leads to a kernel crash since accesses to >> page zero are protected by the kernel for security reasons. >> >> Fix this problem by verifying the contents of pwq and wq before usage. >> Even if probe_kernel_read() usually prevents such crashes by disabling >> page faults, clean code should always include such checks. >> >> Without this fix issuing "echo t > /proc/sysrq-trigger" will immediately >> crash the Linux kernel on the parisc architecture. > > Hmm... um had similar problem but the root cause here is that the arch > isn't implementing probe_kernel_read() properly. We really have no > idea what the pointer value may be at the dump point and that's why we > use probe_kernel_read(). If something like the above is necessary for > the time being, the correct place would be the arch > probe_kernel_read() implementation. James, would it be difficult > implement proper probe_kernel_read() on parisc? No, it's not really complicated. That was my initial way to work around that problem. But is this really necessary? Isn't a pointer which points to mem zero most likely wrong on any architecture? In addition I wrote another patch to work around that problem in the parisc page fault handler (which is needed anyway) too: https://patchwork.kernel.org/patch/2971701/ So, in summary my patch here is not really necessary, but for the sake of clean code I think it doesn't hurt either and as such it would be nice if you could apply it. Helge -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
