On Wed, 2013-10-02 at 00:07 +0200, Helge Deller wrote: > On 10/01/2013 11:40 PM, James Bottomley wrote: > > On Tue, 2013-10-01 at 16:43 -0400, 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? > > > > The problem seems to be that some traps bypass our exception table > > handling. > > Yes, that's correct. > It's trap #26 and we directly call parisc_terminate() for fault_space==0 > without checking the exception table. > See my patch I posted a few hours ago which fixes this: > https://patchwork.kernel.org/patch/2971701/ That doesn't quite look right ... I guessed it was probably access rights, so we should do an exception table fixup, so isn't this the fix? because we shouldn't call do_page_fault if there's no exception table. James --- diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c index 04e47c6..25a088a 100644 --- a/arch/parisc/kernel/traps.c +++ b/arch/parisc/kernel/traps.c @@ -684,6 +684,8 @@ void notrace handle_interruption(int code, struct pt_regs *regs) /* Fall Through */ case 26: /* PCXL: Data memory access rights trap */ + if (!user_mode(regs) && fixup_exception(regs)) + return; fault_address = regs->ior; fault_space = regs->isr; break; -- 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
