Messages in this thread |  | | | From | "H. Peter Anvin" <> | | Subject | Re: copy_from_user() fix | | Date | Wed, 26 Aug 1998 15:59:10 -0700 (PDT) |
| |
> On Wed, Aug 26, 1998 at 04:17:34AM -0700, David S. Miller wrote: > > > Consider a userland pointer verification library that worked in > > about 10 lines of code by passing the pointer in question to a > > sys_write() call to /dev/null... but this wouldn't work actually > > these days due to how the kernel won't even verify the pointer in > > this case. > > Ooo... nice hack. > > You could probably implement this by reading /proc/self/maps anyhow, > it would be several orders of magnitude slower than your suggestion > though. >
Nice hack, except it wouldn't work. Verifying pointers in userland is most easily done by (gack!) reading all bytes of the region in question; on the x86 using a "rep lodsl" (yes, an actual use for rep lodsl).
Not necessarily fast, if the region is large, though; but it's still faster than anything that involves a system call (especially since the kernel does the effectively same thing.)
-hpa
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.altern.org/andrebalsa/doc/lkml-faq.html
|  |