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Message-ID: <CAOiN93mGTu9w9rVNCrbbH1sccXY9VJhaCmg+dS7Rk9mMgKHBaA@mail.gmail.com>
Date: Mon, 8 Jul 2013 10:45:03 +0900
From: Ashish Sangwan <ashishsangwan2@...il.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-arm@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
Ashish Sangwan <a.sangwan@...sung.com>,
Namjae Jeon <namjae.jeon@...sung.com>
Subject: Seg fault occurs when running statically compiled binary from kernel
using call_usermodehelper
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] [<c00171f8>] (dump_backtrace+0x0/0x11c) from
[<c03e8a54>] (dump_stack+0x20/0x24)
[ 36.508000] r6:e514dd80 r5:00000000 r4:e5175fb0 r3:271ae511
[ 36.516000] [<c03e8a34>] (dump_stack+0x0/0x24) from [<c0014174>]
(show_regs+0x58/0x5c)
[ 36.524000] [<c001411c>] (show_regs+0x0/0x5c) from [<c001794c>]
(show_info+0xe0/0x14c)
[ 36.532000] r4:00000000 r3:00000000
[ 36.532000] [<c001786c>] (show_info+0x0/0x14c) from [<c001dfb4>]
(__do_user_fault+0x78/0xc8)
[ 36.540000] r7:80000007 r6:0000000b r5:00000000 r4:e514dd80
[ 36.548000] [<c001df3c>] (__do_user_fault+0x0/0xc8) from
[<c03f4574>] (do_page_fault+0x360/0x3d4)
[ 36.556000] [<c03f4214>] (do_page_fault+0x0/0x3d4) from
[<c0008470>] (do_PrefetchAbort+0x44/0xa8)
[ 36.564000] [<c000842c>] (do_PrefetchAbort+0x0/0xa8) from
[<c03f2bbc>] (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] [<c00171f8>] (dump_backtrace+0x0/0x11c) from
[<c03e8a54>] (dump_stack+0x20/0x24)
[ 36.972000] r6:bf000090 r5:bf00009c r4:e51d7f48 r3:00000000
[ 36.980000] [<c03e8a34>] (dump_stack+0x0/0x24) from [<c008ae88>]
(load_module+0x1a90/0x1eb4)
[ 36.984000] [<c00893f8>] (load_module+0x0/0x1eb4) from [<c008b3b0>]
(sys_init_module+0xe8/0xf8)
[ 36.988000] [<c008b2c8>] (sys_init_module+0x0/0xf8) from
[<c0012dc0>] (ret_fast_syscall+0x0/0x48)
[ 36.992000] r6:bea51a14 r5:bea51b7c r4:00006ee4
[ 36.996000] module2 mod ld
module2.c =>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kmod.h>
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
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