Re: SHA-1 hash calculate in Kernel.

Oct. 22, 2015

      hi all:
       I finally implement it by learning form the function of tcp md5
checksum. This is the relative kernel source
<http://lxr.oss.org.cn/source/net/ipv4/tcp.c?v=2.6.30#L2667>. The SHA-1
implement is here
<https://github.com/lxlenovostar/kernel_test/blob/master/model/kernel_hash/sha.c>.But
I still have a question about __virt_addr_valid.

##############################
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/crypto.h>
#include <linux/err.h>
#include <linux/scatterlist.h>
#include <linux/mm.h>

#define SHA1_LENGTH 20
static inline int phys_addr_valid(resource_size_t addr)
{
#ifdef CONFIG_PHYS_ADDR_T_64BIT
          return !(addr >> boot_cpu_data.x86_phys_bits);
  #else
          return 1;
  #endif
}

bool __virt_addr_valid(unsigned long x)
{
        unsigned long old_x;
        old_x = x;
        //The kernel text is mapped into the region starting
from__START_KERNEL_MAP
        if (x >= __START_KERNEL_map) {
                if (x >= MODULES_VADDR && x <= MODULES_END) {
                    printk(KERN_INFO "right here");
                }
                x -= __START_KERNEL_map;
                 if (x >= KERNEL_IMAGE_SIZE) {
                          printk(KERN_INFO "error1");
                          return false;
                    }
                  x += phys_base;
          } else {
                  if (x < PAGE_OFFSET) {
                          printk(KERN_INFO "error2");
                          return false;
                    }
                  x -= PAGE_OFFSET;
                  if (!phys_addr_valid(x)) {
                          printk(KERN_INFO "error3");
                          return false;
                    }
          }

          return pfn_valid(x >> PAGE_SHIFT);
}

static int minit(void)
{
    /*
     * http://lxr.oss.org.cn/source/fs/ecryptfs/crypto.c?v=2.6.30
     */
    struct scatterlist sg;
    struct hash_desc desc;

    int rc = 0;
    int i;
    char hashtext[SHA1_LENGTH];

    char *plaintext = NULL;
    printk(KERN_INFO "valid=%s\n", virt_addr_valid(plaintext) ? "true" :
"false");
    plaintext = "c";
    printk(KERN_INFO "valid=%s\n", virt_addr_valid(plaintext) ? "true" :
"false");
    size_t len = strlen(plaintext);

    sg_init_one(&sg, (u8 *)plaintext, len);
    desc.tfm = crypto_alloc_hash("sha1", 0, CRYPTO_ALG_ASYNC);
    desc.flags = 0;

    rc = crypto_hash_init(&desc);
    if (rc) {
        printk(KERN_ERR "%s: Error initializing crypto hash; rc = [%d]\n",
__func__, rc);
        goto out;
    }
    rc = crypto_hash_update(&desc, &sg, len);
    if (rc) {
        printk(KERN_ERR "%s: Error updating crypto hash; rc = [%d]\n",
__func__, rc);
        goto out;
    }
    rc = crypto_hash_final(&desc, hashtext);
    if (rc) {
        printk(KERN_ERR "%s: Error finalizing crypto hash; rc = [%d]\n",
__func__, rc);
        goto out;
    }
    crypto_free_hash(desc.tfm);

    for (i = 0; i < 20; i++) {
        //printk(KERN_INFO "%02x-%d\n", hashtext[i]&0xff, i);
    }

out:
    return rc;
}

static void mexit(void)
{
    printk("Exit %s.\n", THIS_MODULE->name);
}
##############################

I make and insmod it. the log is:

##############################
[root@localhost sha]# dmesg -c
error2
valid=false
right here
error1
valid=false
##############################

I think plaintext is between MODULES_VADDR and MODULES_END, So why the
address in
MODULES not a valid virtual address?

Thank you.

2015-08-29 19:49 GMT+08:00 Bernd Petrovitsch <bernd@petrovitsch.priv.at>:
...
On Fre, 2015-08-28 at 15:36 +0800, lx wrote:
[...]
...
//way 2
    /*
    char *plaintext = kmalloc(sizeof(char), GFP_KERNEL);
    plaintext = "c";
I don't think that this line doesn't give any warning ...
Kind regards,
        Bernd
--
"I dislike type abstraction if it has no real reason. And saving
on typing is not a good reason - if your typing speed is the main
issue when you're coding, you're doing something seriously wrong."
    - Linus Torvalds