Messages in this thread | | | Date | Thu, 27 Aug 1998 09:01:58 +1000 | From | Richard Gooch <> | Subject | Re: copy_from_user() fix |
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H. Peter Anvin writes: > > 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.)
Assuming that you can set up the signal handler once and forget it. Not true for a library. Also assuming that you don't need to pass the buffer to a syscall in the first place.
Regards,
Richard....
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