On Fri, 12 Aug 2005 at 15:25:18 +0100 (BST), Hugh Dickins wrote:
> On Thu, 11 Aug 2005, Steven Rostedt wrote:
> >
> > Found the problem. It is a bug with mmap_kmem. The order of checks is
> > wrong, so here's the patch.
>
> Good find, looks right to me, so far as it goes (why does this check
Even with Steven's patch applied, root cannot read from /dev/kmem with the
following program, which works on 2.6.9. "Invalid argument" means that the
"fd is attached to an object that is unsuitable for reading."
# ./desc2
GDT is at 0xc13097a0
read /dev/kmem: Invalid argument
#include <stdio.h>
#include <fcntl.h>
#define perr(err) { perror(err), exit(1); }
struct {
unsigned short limit;
unsigned int base;
} __attribute__ ((packed)) dtr;
int kmem, i;
int buf[1024];
int main() {
if ((kmem = open("/dev/kmem", O_RDONLY)) < 0)
perr("open /dev/kmem");
asm("sgdtl %0" : "=m"(dtr));
printf("GDT is at 0x%x\n", dtr.base);
dtr.limit++; /* convert to size */
if (lseek(kmem, dtr.base, SEEK_SET) != dtr.base)
perr("lseek /dev/kmem");
if (read(kmem, buf, dtr.limit) != dtr.limit)
perr("read /dev/kmem");
for (i = 0; i < dtr.limit / 4; i += 2)
if (buf[i+1])
printf("entry %d(0x%x): 0x%x 0x%x\n",
i / 2, i / 2, buf[i], buf[i+1]);
return 0;
}
__
Chuck
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