|
Size: 5588
Comment:
|
Size: 2159
Comment:
|
| Deletions are marked like this. | Additions are marked like this. |
| Line 1: | Line 1: |
| Line 6: | Line 5: |
| memfP is a character device file that is an image of the main memory of the computer. It may be used, for example, to examine (and even patch) the system. Byte addresses in mem are interpreted as physical memory addresses. References to non-existent locations cause errors to be returned. Examining and patching is likely to lead to unexpected results when read-only or write-only bits are present. It is typically created by: mknod -m 660 /dev/mem c 1 1 chown root:kmem /dev/mem The file kmem is the same as mem , except that the kernel virtual memory rather than physical memory is accessed. It is typically created by: mknod -m 640 /dev/kmem c 1 2 chown root:kmem /dev/kmem portfP is similar to mem , but the I/O ports are accessed. It is typically created by: mknod -m 660 /dev/port c 1 4 chown root:mem /dev/port |
. memfP is a character device file that is an image of the main memory of the computer. It may be used, for example, to examine (and even patch) the system. Byte addresses in mem are interpreted as physical memory addresses. References to non-existent locations cause errors to be returned. Examining and patching is likely to lead to unexpected results when read-only or write-only bits are present. It is typically created by: mknod -m 660 /dev/mem c 1 1 chown root:kmem /dev/mem The file kmem is the same as mem , except that the kernel virtual memory rather than physical memory is accessed. It is typically created by: mknod -m 640 /dev/kmem c 1 2 chown root:kmem /dev/kmem portfP is similar to mem , but the I/O ports are accessed. It is typically created by: mknod -m 660 /dev/port c 1 4 chown root:mem /dev/port |
| Line 17: | Line 10: |
| [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem) [Posted August 16, 2005 by corbet] |
[PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem) [Posted August 16, 2005 by corbet] |
| Line 20: | Line 12: |
| From: Steven Rostedt <rostedt-AT-goodmis.org> To: LKML <linux-kernel-AT-vger.kernel.org> Subject: [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem) Date: Thu, 11 Aug 2005 21:15:02 -0400 Cc: Andrew Morton <akpm-AT-osdl.org>, Linus Torvalds <torvalds-AT-osdl.org> <pre> On Thu, 2005-08-11 at 17:36 -0400, Steven Rostedt wrote: > OK, I thought I use to know this. But what is the difference > between /dev/kmem and /dev/mem. I thought that with /dev/kmem you could > use the actual kernel addresses to read from. > > For example, if I wanted to read the current variable X in the kernel, I > could look up the address of X in System.map, then mmaping to /dev/kmem > I could get to that variable using the address that I got from > System.map. But this doesn't seem to work. > > I'm getting an IO error on read. And looking at this I see: > > > static int mmap_kmem(struct file * file, struct vm_area_struct * vma) > { > unsigned long long val; > /* > * RED-PEN: on some architectures there is more mapped memory > * than available in mem_map which pfn_valid checks > * for. Perhaps should add a new macro here. > * > * RED-PEN: vmalloc is not supported right now. > */ > if (!pfn_valid(vma->vm_pgoff)) > return -EIO; > val = (u64)vma->vm_pgoff << PAGE_SHIFT; > vma->vm_pgoff = __pa(val) >> PAGE_SHIFT; > return mmap_mem(file, vma); > } > > I printed out the value in vma->vm_pgoff, and it still has the > 0xc0000000 (but shifted >> 12). Isn't this suppose to also remove the > 0xc? Or am I just totally off here? > > Thanks, > > -- Steve > |
From: Steven Rostedt <rostedt-AT-goodmis.org> To: LKML <linux-kernel-AT-vger.kernel.org> Subject: [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem) Date: Thu, 11 Aug 2005 21:15:02 -0400 Cc: Andrew Morton <akpm-AT-osdl.org>, Linus Torvalds <torvalds-AT-osdl.org> |
| Line 68: | Line 15: |
| Found the problem. It is a bug with mmap_kmem. The order of checks is wrong, so here's the patch. Attached is a little program that reads the System map looking for the variable modprobe_path. If it finds it, then it opens /dev/kmem for read only and mmaping it to read the contents of modprobe_path. Without this fix I get: # ./tmap /boot/System.map found modprobe_path at (0xc03647e0) c03647e0 mmap: Input/output error On a machine with the patch, I now get: # ./tmap /boot/System.map found modprobe_path at (0xc03aa900) c03aa900 /sbin/modprobe Note that the attached program does not handle the case of the string crossing over a page. -- Steve Here's the simple patch: Signed-off-by: Steven Rostedt <rostedt@goodmis.org> --- linux-2.6.13-rc6-git1/drivers/char/mem.c.orig 2005-08-11 20:48:34.000000000 -0400 +++ linux-2.6.13-rc6-git1/drivers/char/mem.c 2005-08-11 20:48:48.000000000 -0400 @@ -269,10 +269,10 @@ static int mmap_kmem(struct file * file, * * RED-PEN: vmalloc is not supported right now. */ - if (!pfn_valid(vma->vm_pgoff)) - return -EIO; val = (u64)vma->vm_pgoff << PAGE_SHIFT; vma->vm_pgoff = __pa(val) >> PAGE_SHIFT; + if (!pfn_valid(vma->vm_pgoff)) + return -EIO; return mmap_mem(file, vma); } |
|
| Line 112: | Line 17: |
| #include <stdio.h> #include <stdlib.h> #include <string.h> #include <stdarg.h> #include <fcntl.h> #include <unistd.h> #include <errno.h> |
|
| Line 120: | Line 18: |
| #include <sys/types.h> #include <sys/stat.h> #include <sys/poll.h> #include <sys/mman.h> |
|
| Line 125: | Line 19: |
| int page_size; #define PAGE_SIZE page_size #define PAGE_MASK (~(PAGE_SIZE-1)) |
|
| Line 129: | Line 20: |
| void get_var (unsigned long addr) { off_t ptr = addr & ~(PAGE_MASK); off_t offset = addr & PAGE_MASK; int i = 0; char *map; static int kfd = -1; |
~+http://lwn.net/Articles/147902/ |
| Line 136: | Line 22: |
| kfd = open("/dev/kmem",O_RDONLY); if (kfd < 0) { perror("open"); exit(0); } |
+~ |
| Line 142: | Line 24: |
| map = mmap(NULL,PAGE_SIZE,PROT_READ,MAP_SHARED,kfd,offset); if (map == MAP_FAILED) { perror("mmap"); exit(-1); } printf("%s\n",map+ptr); |
~+[Posted August 16, 2005 by corbet] +~ ~+ +~ |
| Line 149: | Line 26: |
| return; } |
~+ +~~+ +~~+ +~~+ +~~+ +~ ||<^>~+'''From''':+~||~+ +~||<^>~+Steven Rostedt <rostedt-AT-goodmis.org>+~|| ||<^>~+'''To''':+~||~+ +~||<^>~+LKML <linux-kernel-AT-vger.kernel.org>+~|| ||<^>~+'''Subject''':+~||~+ +~||<^>~+[PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/'''kmem''' and /dev/mem)+~|| ||<^>~+'''Date''':+~||~+ +~||<^>~+Thu, 11 Aug 2005 21:15:02 -0400+~|| ||<^>~+'''Cc''':+~||~+ +~||<^>~+Andrew Morton <akpm-AT-osdl.org>, Linus Torvalds <torvalds-AT-osdl.org>+~|| {{{ }}} |
| Line 152: | Line 35: |
| int main(int argc, char **argv) { FILE *fp; char addr_str[11]="0x"; char var[51]; unsigned long addr; char ch; int r; if (argc != 2) { fprintf(stderr,"usage: %s System.map\n",argv[0]); exit(-1); } |
|
| Line 166: | Line 36: |
| if ((fp = fopen(argv[1],"r")) == NULL) { perror("fopen"); exit(-1); } |
|
| Line 171: | Line 37: |
| do { r = fscanf(fp,"%8s %c %50s\n",&addr_str[2],&ch,var); if (strcmp(var,"modprobe_path")==0) break; } while(r > 0); if (r < 0) { printf("could not find modprobe_path\n"); exit(-1); } page_size = getpagesize(); addr = strtoul(addr_str,NULL,16); printf("found modprobe_path at (%s) %08lx\n",addr_str,addr); get_var(addr); } |
|
| Line 186: | Line 38: |
| </pre> |
Here is how the kmem can be statically created:
http://kerneltrap.org/man/linux/man4/kmem.4
- memfP is a character device file that is an image of the main memory of the computer. It may be used, for example, to examine (and even patch) the system. Byte addresses in mem are interpreted as physical memory addresses. References to non-existent locations cause errors to be returned. Examining and patching is likely to lead to unexpected results when read-only or write-only bits are present. It is typically created by: mknod -m 660 /dev/mem c 1 1 chown root:kmem /dev/mem The file kmem is the same as mem , except that the kernel virtual memory rather than physical memory is accessed. It is typically created by: mknod -m 640 /dev/kmem c 1 2 chown root:kmem /dev/kmem portfP is similar to mem , but the I/O ports are accessed. It is typically created by: mknod -m 660 /dev/port c 1 4 chown root:mem /dev/port
And here is the description on the difference between kmem and mem.
http://lwn.net/Articles/147902/
[PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem) [Posted August 16, 2005 by corbet]
From: Steven Rostedt <rostedt-AT-goodmis.org> To: LKML <linux-kernel-AT-vger.kernel.org> Subject: [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem) Date: Thu, 11 Aug 2005 21:15:02 -0400 Cc: Andrew Morton <akpm-AT-osdl.org>, Linus Torvalds <torvalds-AT-osdl.org>
http://lwn.net/Articles/147902/
[Posted August 16, 2005 by corbet]
From: |
Steven Rostedt <rostedt-AT-goodmis.org> |
|
To: |
LKML <linux-kernel-AT-vger.kernel.org> |
|
Subject: |
[PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem) |
|
Date: |
Thu, 11 Aug 2005 21:15:02 -0400 |
|
Cc: |
Andrew Morton <akpm-AT-osdl.org>, Linus Torvalds <torvalds-AT-osdl.org> |