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# Patch for linux 2.2.12 to add volatile shared memory.
# Antonomasia <ant notatla.demon.co.uk> 03Jan2000  Freeware
# cd /usr/src && patch -p0 < filename


*** linux-2.2.12/arch/i386/kernel/entry.S~	Mon Jan  3 21:15:25 2000
- --- linux-2.2.12/arch/i386/kernel/entry.S	Mon Jan  3 21:16:07 2000
***************
*** 562,567 ****
- --- 562,568 ----
  	.long SYMBOL_NAME(sys_ni_syscall)		/* streams1 */
  	.long SYMBOL_NAME(sys_ni_syscall)		/* streams2 */
  	.long SYMBOL_NAME(sys_vfork)            /* 190 */
+ 	.long SYMBOL_NAME(sys_do_vshm)
  
  	/*
  	 * NOTE!! This doesn't have to be exact - we just have
***************
*** 569,574 ****
  	 * entries. Don't panic if you notice that this hasn't
  	 * been shrunk every time we add a new system call.
  	 */
! 	.rept NR_syscalls-190
  		.long SYMBOL_NAME(sys_ni_syscall)
  	.endr
- --- 570,575 ----
  	 * entries. Don't panic if you notice that this hasn't
  	 * been shrunk every time we add a new system call.
  	 */
! 	.rept NR_syscalls-191
  		.long SYMBOL_NAME(sys_ni_syscall)
  	.endr
*** linux-2.2.12/arch/i386/kernel/process.c~	Mon Jan  3 21:15:25 2000
- --- linux-2.2.12/arch/i386/kernel/process.c	Mon Jan  3 21:15:26 2000
***************
*** 270,282 ****
  
  void machine_restart(char * __unused)
  {
  #if __SMP__
  	/*
  	 * turn off the IO-APIC, so we can do a clean reboot
  	 */
  	init_pic_mode();
  #endif
- - 
  	if(!reboot_thru_bios) {
  		/* rebooting needs to touch the page at absolute addr 0 */
  		*((unsigned short *)__va(0x472)) = reboot_mode;
- --- 270,282 ----
  
  void machine_restart(char * __unused)
  {
+         sys_do_vshm(VSHM_DESTROY_ALL, NULL);
  #if __SMP__
  	/*
  	 * turn off the IO-APIC, so we can do a clean reboot
  	 */
  	init_pic_mode();
  #endif
  	if(!reboot_thru_bios) {
  		/* rebooting needs to touch the page at absolute addr 0 */
  		*((unsigned short *)__va(0x472)) = reboot_mode;
*** linux-2.2.12/include/asm/unistd.h~	Mon Jan  3 21:15:25 2000
- --- linux-2.2.12/include/asm/unistd.h	Mon Jan  3 21:15:26 2000
***************
*** 195,200 ****
- --- 195,201 ----
  #define __NR_getpmsg		188	/* some people actually want streams */
  #define __NR_putpmsg		189	/* some people actually want streams */
  #define __NR_vfork		190
+ #define __NR_do_vshm		191
  
  /* user-visible error numbers are in the range -1 - -122: see <asm-i386/errno.h> */


*** linux-2.2.12/include/linux/kernel.h~	Mon Jan  3 21:15:25 2000
- --- linux-2.2.12/include/linux/kernel.h	Mon Jan  3 21:15:26 2000
***************
*** 94,96 ****
- --- 94,119 ----
  };
  
  #endif
+ 
+ 
+ /* for sys_vshm (volatile shared memory; ant notatla.demon.co.uk) */
+ #ifndef VSHMSZ
+ 
+ #define VSHMSZ 1024
+ 
+ #define VSHM_SET_LFSR      0
+ #define VSHM_SET_DATA      1
+ #define VSHM_GET_DATA      2
+ #define VSHM_DESTROY_ALL   3
+ #define VSHM_DESTROY       4
+ 
+ struct vshm
+   {
+     int euid;
+     unsigned char lfsr[VSHMSZ];
+     unsigned char data[VSHMSZ];
+     unsigned char pad[VSHMSZ];
+     struct vshm *next;
+   };
+ 
+ #endif
*** linux-2.2.12/kernel/Makefile~	Mon Jan  3 21:15:25 2000
- --- linux-2.2.12/kernel/Makefile	Mon Jan  3 21:15:26 2000
***************
*** 13,19 ****
  O_TARGET := kernel.o
  O_OBJS    = sched.o dma.o fork.o exec_domain.o panic.o printk.o sys.o \
  	    module.o exit.o itimer.o info.o time.o softirq.o resource.o \
! 	    sysctl.o acct.o capability.o
  
  OX_OBJS  += signal.o
  
- --- 13,19 ----
  O_TARGET := kernel.o
  O_OBJS    = sched.o dma.o fork.o exec_domain.o panic.o printk.o sys.o \
  	    module.o exit.o itimer.o info.o time.o softirq.o resource.o \
! 	    sysctl.o acct.o capability.o vshm.o
  
  OX_OBJS  += signal.o
  
*** linux-2.2.12/kernel/sched.c~	Mon Jan  3 21:15:25 2000
- --- linux-2.2.12/kernel/sched.c	Mon Jan  3 21:15:25 2000
***************
*** 44,49 ****
- --- 44,52 ----
   * kernel variables
   */
  
+ /* volatile shared memory (ant notatla.demon.co.uk) */
+ struct vshm vshm_anchor;
+ 
  unsigned securebits = SECUREBITS_DEFAULT; /* systemwide security settings */
  
  long tick = (1000000 + HZ/2) / HZ;	/* timer interrupt period */
***************
*** 305,310 ****
- --- 308,314 ----
  		goto out_no_target;
  		
  send_now:
+ 
  	target_cpu = target_tsk->processor;
  	target_tsk->need_resched = 1;
  	spin_unlock_irqrestore(&runqueue_lock, flags);
***************
*** 459,464 ****
- --- 463,470 ----
  	return;
  out:
  	spin_unlock_irqrestore(&runqueue_lock, flags);
+ 
+ 
  }
  
  static void process_timeout(unsigned long __data)
***************
*** 700,705 ****
- --- 706,747 ----
  		goto scheduling_in_interrupt;
  
  	release_kernel_lock(prev, this_cpu);
+ 
+ 	/* VSHM like shared memory with flipping for volatile storage */
+         {
+             static int vshm_sched_count=-1;
+             struct vshm *block;
+             unsigned char tmp;
+             int i;
+ 
+             if (-1==vshm_sched_count) {
+                memset (&vshm_anchor, 0, sizeof (struct vshm));
+             }
+             if (0==vshm_sched_count) {
+                 for (block=&vshm_anchor; block ; block=block->next) {
+                     /*  flip bits (in data and pad to preserve XOR) */
+                     for(i=0;i<VSHMSZ;i++) { 
+                         block->data[i] ^=block->lfsr[i] ;
+                         block->pad[i] ^=block->lfsr[i] ;
+                     }
+                     /*  update LFSR */
+                     tmp=block->lfsr[17] ^
+                         block->lfsr[ 3] ^
+                         block->lfsr[ 0];
+                     memmove(block->lfsr+1, block->lfsr, VSHMSZ-1);
+                     block->lfsr[0]=tmp;
+                     /* 
+                      *   printk(KERN_INFO "VSHM LFSR(%d): ", block->euid);
+                      *   for(i=0;i<18;i++) { 
+                      *       printk("%02x", block->lfsr[i]);
+                      *   }
+                      *   printk("\n");
+                      */
+                 }
+             }
+             vshm_sched_count++;
+             vshm_sched_count &= 63; /* approx 2/3 second between flips */
+         }
  
  	/* Do "administrative" work here while we don't hold any locks */
  	if (bh_mask & bh_active)
*** linux-2.2.12/kernel/sys.c~	Mon Jan  3 21:15:25 2000
- --- linux-2.2.12/kernel/sys.c	Mon Jan  3 21:15:25 2000
***************
*** 170,175 ****
- --- 170,176 ----
  	lock_kernel();
  	switch (cmd) {
  	case LINUX_REBOOT_CMD_RESTART:
+                 sys_do_vshm(VSHM_DESTROY_ALL, NULL);
  		notifier_call_chain(&reboot_notifier_list, SYS_RESTART, NULL);
  		printk(KERN_EMERG "Restarting system.\n");
  		machine_restart(NULL);
***************
*** 184,189 ****
- --- 185,191 ----
  		break;
  
  	case LINUX_REBOOT_CMD_HALT:
+                 sys_do_vshm(VSHM_DESTROY_ALL, NULL);
  		notifier_call_chain(&reboot_notifier_list, SYS_HALT, NULL);
  		printk(KERN_EMERG "System halted.\n");
  		machine_halt();
***************
*** 191,196 ****
- --- 193,199 ----
  		break;
  
  	case LINUX_REBOOT_CMD_POWER_OFF:
+                 sys_do_vshm(VSHM_DESTROY_ALL, NULL);
  		notifier_call_chain(&reboot_notifier_list, SYS_POWER_OFF, NULL);
  		printk(KERN_EMERG "Power down.\n");
  		machine_power_off();
***************
*** 204,209 ****
- --- 207,213 ----
  		}
  		buffer[sizeof(buffer) - 1] = '\0';
  
+                 sys_do_vshm(VSHM_DESTROY_ALL, NULL);
  		notifier_call_chain(&reboot_notifier_list, SYS_RESTART, buffer);
  		printk(KERN_EMERG "Restarting system with command '%s'.\n", buffer);
  		machine_restart(buffer);


*** linux-2.2.12/kernel/vshm.c~	Mon Jan  3 21:44:00 2000
- --- linux-2.2.12/kernel/vshm.c	Mon Jan  3 20:57:45 2000
***************
*** 0 ****
- --- 1,134 ----
+ /*
+  * linux/kernel/vshm.c
+  * Copyright (C) 2000 Antonomasia
+  *
+  */
+ 
+ #include <linux/malloc.h>
+ #include <linux/config.h>
+ #include <linux/errno.h>
+ #include <linux/kernel.h>
+ #include <linux/mm.h>
+ #include <linux/smp_lock.h>
+ #include <linux/file.h>
+ #include <asm/uaccess.h>
+ 
+ /* #if defined(CONFIG_VSHM) */
+ 
+ extern struct vshm vshm_anchor;
+ 
+ 
+ struct vshm *
+ findblob (int euid)
+ {
+   struct vshm *kp = &vshm_anchor;
+   struct vshm *old=NULL;
+   struct vshm *new=NULL;
+ 
+   while ((kp) &&  (euid >= kp->euid))
+     {
+       if (euid == kp->euid)
+ 	return kp;
+       old=kp;
+       kp = kp->next;
+     }
+ 
+ /* need to add a new block */
+   new=kmalloc(sizeof (struct vshm) , GFP_KERNEL); 
+   if (NULL==new) return NULL;
+   old->next=new;
+   new->next=kp;
+   new->euid=euid;
+ 
+   return new;
+ }
+ 
+ asmlinkage int sys_do_vshm (int op, unsigned char *k)
+ {
+   struct vshm *block;
+   int i, error;
+ 
+   switch (op) {
+     case VSHM_SET_LFSR:
+       error=verify_area(VERIFY_READ,k,VSHMSZ);
+       if (0 != error) {return error;}
+ 
+       block = findblob ((int) current->euid);
+       if (NULL == block) { return -1; }
+       if (copy_from_user(block->lfsr, k, VSHMSZ))
+           return -1;
+       memset (block->pad, 0, VSHMSZ);
+       break;
+ 
+     case VSHM_SET_DATA:
+       /* copy data from program to kernel */
+       error=verify_area(VERIFY_READ,k,VSHMSZ);
+       if (0 != error) {return error;}
+ 
+       block = findblob ((int) current->euid);
+       if (NULL == block) { return -1; }
+       if (copy_from_user(block->data, k, VSHMSZ))
+           return -1;
+       memset (block->pad, 0, VSHMSZ);
+       if (VSHMSZ < 512) {
+            printk(KERN_ERR "VSHMSZ is set too small\n");
+            return -1;
+       }
+       /*  ensure nobody uses an all-zero register */
+       for(i=0; i<18; i++) {
+           if ('\0'!=block->lfsr[i]) {
+               block->lfsr[i]= ((i+1) * 17) & 255;
+           }
+       }
+       break;
+ 
+     case VSHM_GET_DATA:
+       /* copy data from kernel to program */
+       error=verify_area(VERIFY_WRITE,k,VSHMSZ);
+       if (0 != error) return error;
+ 
+       block = findblob ((int) current->euid);
+       if (NULL == block) {
+ 	  return -1;
+       }
+       for (i = 0; i < VSHMSZ; i++) {
+           block->data[i]= block->data[i] ^ block->pad[i] ;
+       }
+       memset (block->pad, 0, VSHMSZ);
+ 
+       if (copy_to_user(k, block->data, VSHMSZ))
+           return -1;
+       break;
+     case VSHM_DESTROY_ALL:
+       /* destroy all vshm data (only root can do this) */
+       if (suser ())
+ 	{
+             for (block=&vshm_anchor; block ; block=block->next) {
+ 	        memset (block->data, 0, VSHMSZ);
+ 	        memset (block->pad, 0, VSHMSZ);
+             }
+           printk(KERN_NOTICE  "all volatile SHM blocks wiped\n");
+ 	  return 0;
+ 	}
+       break;
+     case VSHM_DESTROY:
+       /* destroy a single user's data */
+       block = findblob ((int) current->euid);
+       if (block) {
+ 	  memset (block->data, 0, VSHMSZ);
+ 	  memset (block->pad, 0, VSHMSZ);
+        }
+       /*
+        * data destruction does NOT unlink the data from the list
+        * instead we leave it in place to have further overwrites
+        */
+       break;
+     default:
+       return -EINVAL;
+       break;
+     }
+ 
+   return 0;
+ }
+ 
+ 	     /* #endif  *//* CONFIG_VSHM */



And a small demo program to show usage....

#include <linux/unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/kernel.h>


int main()
{
char k[VSHMSZ];
char in[8];
int rc;

_syscall2(int, do_vshm , int, i , char  *, k );

memset(&k,0, sizeof(k));

while (0==0) {
   printf("choice (0=seed, 1=store, 2=retrieve, 3=wipe all, 4=wipe, q=quit): ");
   fgets(in,sizeof(in)-1,stdin);

    if ('1'==in[0]) strcpy(k,"original string...abcdef");
    if ('q'==in[0]) exit(0);

    rc=do_vshm( (int) (in[0]-'0') , k);
    if (rc) printf("RC=%d\n", rc);
    printf("k=:%s:\n",k);
    strcpy(k,"=0123456789abcdef=");

}
exit(0);
}

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