Re: copy_from_user problem

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2008-02-25 at 19:47 -0600, Maynard Johnson wrote:
> Hi,
> I'm developing a kernel module that needs to parse the in-memory ELF 
> objects for a shared library (libc, to be specific).  When running my 
> test on a 32-bit library, it works fine, but for a 64-bit library, the 
> very first copy_from_user() fails:
>     Elf64_Ehdr ehdr;
>     copy_from_user(&ehdr, location_of_lib, sizeof(Elf64_Ehdr);
> 
> I talked this over a bit with Will Schmidt.  He determined that 
> access_ok (being done as a result of copy_from_user) was failing, but we 
> don't know why.  I have 32-bit and 64-bit testcases that start up and 
> then pause, waiting for input.  We look at the entry for libc in 
> /proc/<pid>/maps, and the permissions are the same for both 32-bit and 
> 64-bit.
> 
> I've run this test on both a stock SLES 10 SP1 kernel and on 2.6.24. 
> I'm sure this is a user error, but for the life of me, I don't know what 
> I'm doing wrong.
> 
> Can anyone out there help?

I would have to look at the code.

Ben.