Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753475Ab3GHBpc (ORCPT ); Sun, 7 Jul 2013 21:45:32 -0400 Received: from mail-qe0-f41.google.com ([209.85.128.41]:47989 "EHLO mail-qe0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753326Ab3GHBpF (ORCPT ); Sun, 7 Jul 2013 21:45:05 -0400 MIME-Version: 1.0 Date: Mon, 8 Jul 2013 10:45:03 +0900 Message-ID: Subject: Seg fault occurs when running statically compiled binary from kernel using call_usermodehelper From: Ashish Sangwan To: Al Viro Cc: linux-arm@lists.infradead.org, LKML , Ashish Sangwan , Namjae Jeon Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5675 Lines: 153 On kernel version 3.8.13, when we try to execute a statically compiled binary from kernel, it is giving segfault: insmod /mnt/module2.ko [ 35.560000] sample.static: unhandled page fault (11) at 0x00000000, code 0x80000007 [ 36.440000] Pid: 257, comm: sample.static [ 36.444000] CPU: 3 Tainted: G W O (3.8.13+ #35) [ 36.448000] PC is at 0x0 [ 36.452000] LR is at 0xa420 [ 36.456000] pc : [<00000000>] lr : [<0000a420>] psr: 60000030 [ 36.456000] sp : beb30d70 ip : 00000004 fp : 00000000 [ 36.464000] r10: 0000a004 r9 : 0000a0a4 r8 : 00000001 [ 36.472000] r7 : 00000001 r6 : 0008be5c r5 : 00000000 r4 : 0008ce80 [ 36.476000] r3 : 00000001 r2 : 00000001 r1 : 00000000 r0 : 00000000 [ 36.484000] Flags: nZCv IRQs on FIQs on Mode USER_32 ISA Thumb Segment user [ 36.492000] Control: 10c53c7d Table: 7b1f806a DAC: 00000015 [ 36.496000] Backtrace: [ 36.500000] [] (dump_backtrace+0x0/0x11c) from [] (dump_stack+0x20/0x24) [ 36.508000] r6:e514dd80 r5:00000000 r4:e5175fb0 r3:271ae511 [ 36.516000] [] (dump_stack+0x0/0x24) from [] (show_regs+0x58/0x5c) [ 36.524000] [] (show_regs+0x0/0x5c) from [] (show_info+0xe0/0x14c) [ 36.532000] r4:00000000 r3:00000000 [ 36.532000] [] (show_info+0x0/0x14c) from [] (__do_user_fault+0x78/0xc8) [ 36.540000] r7:80000007 r6:0000000b r5:00000000 r4:e514dd80 [ 36.548000] [] (__do_user_fault+0x0/0xc8) from [] (do_page_fault+0x360/0x3d4) [ 36.556000] [] (do_page_fault+0x0/0x3d4) from [] (do_PrefetchAbort+0x44/0xa8) [ 36.564000] [] (do_PrefetchAbort+0x0/0xa8) from [] (ret_from_exception+0x0/0x10) [ 36.572000] Exception stack(0xe5175fb0 to 0xe5175ff8) [ 36.960000] do_init_module: 'module2'->init suspiciously returned 11, it should follow 0/-E convention [ 36.960000] do_init_module: loading module anyway... [ 36.964000] Backtrace: [ 36.968000] [] (dump_backtrace+0x0/0x11c) from [] (dump_stack+0x20/0x24) [ 36.972000] r6:bf000090 r5:bf00009c r4:e51d7f48 r3:00000000 [ 36.980000] [] (dump_stack+0x0/0x24) from [] (load_module+0x1a90/0x1eb4) [ 36.984000] [] (load_module+0x0/0x1eb4) from [] (sys_init_module+0xe8/0xf8) [ 36.988000] [] (sys_init_module+0x0/0xf8) from [] (ret_fast_syscall+0x0/0x48) [ 36.992000] r6:bea51a14 r5:bea51b7c r4:00006ee4 [ 36.996000] module2 mod ld module2.c => #include #include #include MODULE_LICENSE( "GPL" ); static int test( void ) { char *argv[] = { "/mnt/sample.static", NULL }; static char *envp[] = { "HOME=/", "TERM=linux", "PATH=/sbin:/bin:/usr/sbin:/usr/bin", NULL }; return call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC ); } static int __init mod_entry_func( void ) { return test(); } static void __exit mod_exit_func( void ) { return; } module_init( mod_entry_func ); module_exit( mod_exit_func ); sample.static is a simple "Hello_world" program. However, there is no problem in executing dynamically compiled binaries. When we revert commit 9fff2fa0db911b0b75ec1f9bec72460c0a676ef5 (arm: switch to saner kernel_execve() semantics), there is no problem. OR for kernel 3.8.13 (which is just a plain revert when arch specific kernel_execve was present), then also no problem => diff --git a/kernel/kmod.c b/kernel/kmod.c index 0023a87..9cf6e15 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -184,6 +184,10 @@ static int ____call_usermodehelper(void *data) struct subprocess_info *sub_info = data; struct cred *new; int retval; +#ifdef ARM + struct pt_regs regs; + struct pt_regs *curr_ptr; +#endif spin_lock_irq(¤t->sighand->siglock); flush_signal_handlers(current, 1); @@ -222,6 +226,36 @@ static int ____call_usermodehelper(void *data) retval = do_execve(sub_info->path, (const char __user *const __user *)sub_info->argv, (const char __user *const __user *)sub_info->envp); + +#ifdef ARM + if (retval) + goto fail; + curr_ptr = current_pt_regs(); + memcpy(®s, curr_ptr, sizeof(struct pt_regs)); + /* + * Save argc to the register structure for userspace. + */ + regs.ARM_r0 = retval; + + /* + * We were successful. We won't be returning to our caller, but + * instead to user space by manipulating the kernel stack. + */ + asm( "add r0, %0, %1\n\t" + "mov r1, %2\n\t" + "mov r2, %3\n\t" + "bl memmove\n\t" /* copy regs to top of stack */ + "mov r8, #0\n\t" /* not a syscall */ + "mov r9, %0\n\t" /* thread structure */ + "mov sp, r0\n\t" /* reposition stack pointer */ + "b ret_to_user" + : + : "r" (current_thread_info()), + "Ir" (THREAD_START_SP - sizeof(regs)), + "r" (®s), + "Ir" (sizeof(regs)) + : "r0", "r1", "r2", "r3", "r8", "r9", "ip", "lr", "memory"); +#endif if (!retval) return 0; -- Please suggest a proper solution. Regards, Ashish -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/