Re: [uml-devel] [PATCH] fix writing into /dev/kmem

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Alle 03:36, domenica 29 febbraio 2004, Jeff Dike ha scritto:
> The patch below fixes a bug in the /dev/kmem driver which causes UML to
> die if you write to it.  Of course, the kernel will die if you write random
> crap to kernel memory, but at least it doesn't die in a UML-specific way.

> This is a cut'n'paste from an xterm, so apply with patch -l.

This patch is like the one for the read from /dev/kmem (i.e. the one fixing 
the panic when one does "cat /dev/kmem": you can reproduce this panic on 
Uml2.6): it makes it behave like /dev/mem (man 4 mem is indeed helpful!). So 
it is basically not *the right way*.

Also, someone got a panic with the read patch applied while klogd was reading 
something. The diagnosys was that the /dev/mem driver checks for overflows, 
while this patched /dev/kmem driver does not. To read the physical address 
0x1with /dev/kmem, you are supposed to read 0xc0000001; so with that patch 
any proper user of /dev/kmem will overflow p.

So, I propose to either return -EFAULT with not accessible addresses (which is 
the proper fix), or to (at least and as a workaround) correct the "fops" 
fields of /dev/kmem to redirect it on /dev/mem (at least this avoids the 
crash better than the current patches).
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729



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