I am working on kernel extension and want to find out how to find process name by pid in kernel extension
This code works great in user space
static char procdata[4096];
int mib[3] = { CTL_KERN, KERN_PROCARGS, pid };
procdata[0] = '\0'; // clear
size_t size = sizeof(procdata);
if (sysctl(mib, 3, procdata, &size, NULL, 0)) {
return ERROR(ERROR_INTERNAL);
}
procdata[sizeof(procdata)-2] = ':';
procdata[sizeof(procdata)-1] = '\0';
ret = procdata;
return SUCCESS;
but for the kernel space, there are errors such as "Use of undeclared identifier 'CTL_KERN'" (even if I add #include )
What is the correct way to do it in kernel extension?
The Kernel.framework header <sys/proc.h> is what you're looking for.
In particular, you can use proc_name() to get a process's name given its PID:
/* this routine copies the process's name of the executable to the passed in buffer. It
* is always null terminated. The size of the buffer is to be passed in as well. This
* routine is to be used typically for debugging
*/
void proc_name(int pid, char * buf, int size);
Note however, that the name will be truncated to MAXCOMLEN - 16 bytes.
You might also be able to use the sysctl via sysctlbyname() from the kernel. In my experience, that function doesn't work well though, as the sysctl buffer memory handling isn't expecting buffers in kernel address space, so most types of sysctl will cause a kernel panic if called from a non-kernel thread. It also doesn't seem to work for all sysctls.
Related
I'm seeing a weird case in a simple linux driver test(arm64).
The user program calls ioctl of a device driver and passes array 'arg' of uint64_t as argument. By the way, arg[2] contains a pointer to a variable in the app. Below is the code snippet.
case SetRunParameters:
copy_from_user(args, (void __user *)arg, 8*3);
offs = args[2] % PAGE_SIZE;
down_read(¤t->mm->mmap_sem);
res = get_user_pages( (unsigned long)args[2], 1, 1, &pages, NULL);
if (res) {
kv_page_addr = kmap(pages);
kv_addr = ((unsigned long long int)(kv_page_addr)+offs);
args[2] = page_to_phys(pages) + offset; // args[2] changed to physical
}
else {
printk("get_user_pages failed!\n");
}
up_read(¤t->mm->mmap_sem);
*(vaddr + REG_IOCTL_ARG/4) = virt_to_phys(args); // from axpu_regs.h
printk("ldd:writing %x at %px\n",cmdx,vaddr + REG_IOCTL_CMD/4); // <== line 248. not ok w/o this printk line why?..
*(vaddr + REG_IOCTL_CMD/4) = cmdx; // this command is different from ioctl cmd!
put_page(pages); //page_cache_release(page);
break;
case ...
I have marked line 248 in above code. If I comment out the printk there, a trap occurs and the virtual machine collapses(I'm doing this on a qemu virtual machine). The cmdx is a integer value set according to the ioctl command from the app, and vaddr is the virtual address of the device (obtained from ioremap). If I keep the printk, it works as I expect. What case can make this happen? (cache or tlb?)
Accessing memory-mapped registers by simple C constructs such as *(vaddr + REG_IOCTL_ARG/4) is a bad idea. You might get away with it on some platforms if the access is volatile-qualified, but it won't work reliably or at all on some platforms. The proper way to access memory-mapped registers is via the functions declared by #include <asm/io.h> or #include <linux/io.h>. These will take care of any arch-specific requirements to ensure that writes are properly ordered as far as the CPU is concerned1.
The functions for memory-mapped register access are described in the Linux kernel documentation under Bus-Independent Device Accesses.
This code:
*(vaddr + REG_IOCTL_ARG/4) = virt_to_phys(args);
*(vaddr + REG_IOCTL_CMD/4) = cmdx;
can be rewritten as:
writel(virt_to_phys(args), vaddr + REG_IOCTL_ARG/4);
writel(cmdx, vaddr + REG_IOCTL_CMD/4);
1 Write-ordering for specific bus types such as PCI may need extra code to read a register inbetween writes to different registers if the ordering of the register writes is important. That is because writes are "posted" asynchronously to the PCI bus, and the PCI device may process writes to different registers out of order. An intermediate register read will not be handled by the device until all preceding writes have been handled, so it can be used to enforce ordering of posted writes.
My kernel module code needs to send signal [def.] to a user land program, to transfer its execution to registered signal handler.
I know how to send signal between two user land processes, but I can not find any example online regarding the said task.
To be specific, my intended task might require an interface like below (once error != 1, code line int a=10 should not be executed):
void __init m_start(){
...
if(error){
send_signal_to_userland_process(SIGILL)
}
int a = 10;
...
}
module_init(m_start())
An example I used in the past to send signal to user space from hardware interrupt in kernel space. That was just as follows:
KERNEL SPACE
#include <asm/siginfo.h> //siginfo
#include <linux/rcupdate.h> //rcu_read_lock
#include <linux/sched.h> //find_task_by_pid_type
static int pid; // Stores application PID in user space
#define SIG_TEST 44
Some "includes" and definitions are needed. Basically, you need the PID of the application in user space.
struct siginfo info;
struct task_struct *t;
memset(&info, 0, sizeof(struct siginfo));
info.si_signo = SIG_TEST;
// This is bit of a trickery: SI_QUEUE is normally used by sigqueue from user space, and kernel space should use SI_KERNEL.
// But if SI_KERNEL is used the real_time data is not delivered to the user space signal handler function. */
info.si_code = SI_QUEUE;
// real time signals may have 32 bits of data.
info.si_int = 1234; // Any value you want to send
rcu_read_lock();
// find the task with that pid
t = pid_task(find_pid_ns(pid, &init_pid_ns), PIDTYPE_PID);
if (t != NULL) {
rcu_read_unlock();
if (send_sig_info(SIG_TEST, &info, t) < 0) // send signal
printk("send_sig_info error\n");
} else {
printk("pid_task error\n");
rcu_read_unlock();
//return -ENODEV;
}
The previous code prepare the signal structure and send it. Bear in mind that you need the application's PID. In my case the application from user space send its PID through ioctl driver procedure:
static long dev_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {
ioctl_arg_t args;
switch (cmd) {
case IOCTL_SET_VARIABLES:
if (copy_from_user(&args, (ioctl_arg_t *)arg, sizeof(ioctl_arg_t))) return -EACCES;
pid = args.pid;
break;
USER SPACE
Define and implement the callback function:
#define SIG_TEST 44
void signalFunction(int n, siginfo_t *info, void *unused) {
printf("received value %d\n", info->si_int);
}
In main procedure:
int fd = open("/dev/YourModule", O_RDWR);
if (fd < 0) return -1;
args.pid = getpid();
ioctl(fd, IOCTL_SET_VARIABLES, &args); // send the our PID as argument
struct sigaction sig;
sig.sa_sigaction = signalFunction; // Callback function
sig.sa_flags = SA_SIGINFO;
sigaction(SIG_TEST, &sig, NULL);
I hope it helps, despite the fact the answer is a bit long, but it is easy to understand.
You can use, e.g., kill_pid(declared in <linux/sched.h>) for send signal to the specified process. To form parameters to it, see implementation of sys_kill (defined as SYSCALL_DEFINE2(kill) in kernel/signal.c).
Note, that it is almost useless to send signal from the kernel to the current process: kernel code should return before user-space program ever sees signal fired.
Your interface is violating the spirit of Linux. Don't do that..... A system call (in particular those related to your driver) should only fail with errno (see syscalls(2)...); consider eventfd(2) or netlink(7) for such asynchronous kernel <-> userland communications (and expect user code to be able to poll(2) them).
A kernel module could fail to be loaded. I'm not familiar with the details (never coded any kernel modules) but this hello2.c example suggests that the module init function can return a non zero error code on failure.
People are really expecting that signals (which is a difficult and painful concept) are behaving as documented in signal(7) and what you want to do does not fit in that picture. So a well behaved kernel module should never asynchronously send any signal to processes.
If your kernel module is not behaving nicely your users would be pissed off and won't use it.
If you want to fork your experimental kernel (e.g. for research purposes), don't expect it to be used a lot; only then could you realistically break signal behavior like you intend to do, and you could code things which don't fit into the kernel module picture (e.g. add a new syscall). See also kernelnewbies.
I'm making code to transfer string in kernel to usermode using systemcall and copy_to_user
here is my code
kernel
#include<linux/kernel.h>
#include<linux/syscalls.h>
#include<linux/sched.h>
#include<linux/slab.h>
#include<linux/errno.h>
asmlinkage int sys_getProcTagSysCall(pid_t pid, char **tag){
printk("getProcTag system call \n\n");
struct task_struct *task= (struct task_struct*) kmalloc(sizeof(struct task_struct),GFP_KERNEL);
read_lock(&tasklist_lock);
task = find_task_by_vpid(pid);
if(task == NULL )
{
printk("corresponding pid task does not exist\n");
read_unlock(&tasklist_lock);
return -EFAULT;
}
read_unlock(&tasklist_lock);
printk("Corresponding pid task exist \n");
printk("tag is %s\n" , task->tag);
/*
task -> tag : string is stored in task->tag (ex : "abcde")
this part is well worked
*/
if(copy_to_user(*tag, task->tag, sizeof(char) * task->tag_length) !=0)
;
return 1;
}
and this is user
#include<stdio.h>
#include<stdlib.h>
int main()
{
char *ret=NULL;
int pid = 0;
printf("PID : ");
scanf("%4d", &pid);
if(syscall(339, pid, &ret)!=1) // syscall 339 is getProcTagSysCall
printf("pid %d does not exist\n", pid);
else
printf("Corresponding pid tag is %s \n",ret); //my output is %s = null
return 0;
}
actually i don't know about copy_to_user well. but I think copy_to_user(*tag, task->tag, sizeof(char) * task->tag_length) is operated like this code
so i use copy_to_user like above
#include<stdio.h>
int re();
void main(){
char *b = NULL;
if (re(&b))
printf("success");
printf("%s", b);
}
int re(char **str){
char *temp = "Gdg";
*str = temp;
return 1;
}
Is this a college assignment of some sort?
asmlinkage int sys_getProcTagSysCall(pid_t pid, char **tag){
What is this, Linux 2.6? What's up with ** instead of *?
printk("getProcTag system call \n\n");
Somewhat bad. All strings are supposed to be prefixed.
struct task_struct *task= (struct task_struct*) kmalloc(sizeof(struct task_struct),GFP_KERNEL);
What is going on here? Casting malloc makes no sense whatsoever, if you malloc you should have used sizeof(*task) instead, but you should not malloc in the first place. You want to find a task and in fact you just overwrite this pointer's value few lines later anyway.
read_lock(&tasklist_lock);
task = find_task_by_vpid(pid);
find_task_by_vpid requires RCU. The kernel would have told you that if you had debug enabled.
if(task == NULL )
{
printk("corresponding pid task does not exist\n");
read_unlock(&tasklist_lock);
return -EFAULT;
}
read_unlock(&tasklist_lock);
So... you unlock... but you did not get any kind of reference to the task.
printk("Corresponding pid task exist \n");
printk("tag is %s\n" , task->tag);
... in other words by the time you do task->tag, the task may already be gone. What requirements are there to access ->tag itself?
if(copy_to_user(*tag, task->tag, sizeof(char) * task->tag_length) !=0)
;
What's up with this? sizeof(char) is guaranteed to be 1.
I'm really confused by this entire business.
When you have a syscall which copies data to userspace where amount of data is not known prior to the call, teh syscall accepts both buffer AND its size. Then you can return appropriate error if the thingy you are trying to copy would not fit.
However, having a syscall in the first place looks incorrect. In linux per-task data is exposed to userspace in /proc/pid/. Figuring out how to add a file to proc is easy and left as an exercise for the reader.
It's quite obvious from the way you fixed it. copy_to_user() will only copy data between two memory regions - one accessible only to kernel and the other accessible also to user. It will not, however, handle any memory allocation. Userspace buffer has to be already allocated and you should pass address of this buffer to the kernel.
One more thing you can change is to change your syscall to use normal pointer to char instead of pointer to pointer which is useless.
Also note that you are leaking memory in your kernel code. You allocate memory for task_struct using kmalloc and then you override the only pointer you have to this memory when calling find_task_by_vpid() and this memory is never freed. find_task_by_vpid() will return a pointer to a task_struct which already exists in memory so there is no need to allocate any buffer for this.
i solved my problem by making malloc in user
I changed
char *b = NULL;
to
char *b = (char*)malloc(sizeof(char) * 100)
I don't know why this work properly. but as i guess copy_to_user get count of bytes as third argument so I should malloc before assigning a value
I don't know. anyone who knows why adding malloc is work properly tell me
I am trying to fix a problem in code I am not familiar with. I have traced it down to call to WriteProcessMemory always failing with ERROR_INVALID_ADDRESS. I have no idea why it fails.I tried to check if my process has the required access to write to its child process using VirtualQUery and it does. Can anyone shed some light on this? The code path is extremely convoluted so I have skipped a lot of it. Please let me know if left out any info.
CreateProcessAsUserW(hToken, exe, cmd_line,
NULL, // No security attribute.
NULL, // No thread attribute.
false, // do not inherit handles
CREATE_SUSPENDED | CREATE_UNICODE_ENVIRONMENT | DETACHED_PROCESS | EXTENDED_STARTUPINFO_PRESENT | CREATE_BREAKAWAY_FROM_JOB, // start suspended, extended startup info, break out of job
NULL, // Use the environment of the caller
NULL, // Use current directory of the caller.
&si,
&pi);
/*
....lots of work here
*/
void* address = {...};
void* var = address; // note this line
SIZE_T written;
if(!WriteProcessMemory( pi.handle,
var, address, // not completely sure what it is doing here - writing contents of address to address of var?
size, &written))
{
DWORD error = GetLastError(); // ERROR_INVALID_ADDRESS
MEMORY_BASIC_INFORMATION buffer;
SIZE_T num = VirtualQuery(address,&buffer,sizeof(MEMORY_BASIC_INFORMATION));
if(num > 0)
{
DWORD access = buffer.AllocationProtect; // PAGE_EXECUTE_WRITECOPY
DWORD state = buffer.State; // MEM_COMMIT
DWORD type = buffer.Type;
}
}
This is a 32-bit process running on 64-bit Win7.
You're performing a local VirtualQuery before trying to write into another process, whose address space may be wildly different.
If you want to be sure to have a valid pointer in that process's adress space, either you find where that process puts what interests you (good luck with ASLR), or you allocate some memory for you within that process (with, say VirtualAllocEx()).
Note: If you actually want shared memory, you should use CreateFileMapping(INVALID_HANDLE_VALUE) instead.
I am newbei to driver programming i am started writing the simple char driver . Then i created special file for my char driver mknod /dev/simple-driver c 250 0 .when it type cat /dev/simple-driver. it shows the string "Hello world from Kernel mode!". i know that function
static const char g_s_Hello_World_string[] = "Hello world tamil_vanan!\n\0";
static const ssize_t g_s_Hello_World_size = sizeof(g_s_Hello_World_string);
static ssize_t device_file_read(
struct file *file_ptr
, char __user *user_buffer
, size_t count
, loff_t *possition)
{
printk( KERN_NOTICE "Simple-driver: Device file is read at offset =
%i, read bytes count = %u", (int)*possition , (unsigned int)count );
if( *possition >= g_s_Hello_World_size )
return 0;
if( *possition + count > g_s_Hello_World_size )
count = g_s_Hello_World_size - *possition;
if( copy_to_user(user_buffer, g_s_Hello_World_string + *possition, count) != 0 )
return -EFAULT;
*possition += count;
return count;
}
is get called . This is mapped to (*read) in file_opreation structure of my driver .My question is how this function is get called , how the parameters like struct file,char,count, offset are passed bcoz is i simply typed cat command ..Please elabroate how this happening
In Linux all are considered as files. The type of file, whether it is a driver file or normal file depends upon the mount point where it is mounted.
For Eg: If we consider your case : cat /dev/simple-driver traverses back to the mount point of device files.
From the device file name simple-driver it retrieves Major and Minor number.
From those number(especially from minor number) it associates the driver file for your character driver.
From the driver it uses struct file ops structure to find the read function, which is nothing but your read function:
static ssize_t device_file_read(struct file *file_ptr, char __user *user_buffer, size_t count, loff_t *possition)
User_buffer will always take sizeof(size_t count).It is better to keep a check of buffer(In some cases it throws warning)
String is copied to User_buffer(copy_to_user is used to check kernel flags during copy operation).
postion is 0 for first copy and it increments in the order of count:position+=count.
Once read function returns the buffer to cat. and cat flushes the buffer contents on std_out which is nothing but your console.
cat will use some posix version of read call from glibc. Glibc will put the arguments on the stack or in registers (this depends on your hardware architecture) and will switch to kernel mode. In the kernel the values will be copied to the kernel stack. And in the end your read function will be called.