Is it possible to execute a custom function on the entry crud methods? Is it possible to execute a custom function on the entry crud methods? Basically what I want to achieve is that a CP user with certain field value cannot read or save an entry that doesn't have the same field value. (in this case company) Are there any hooks/events available on that level? On group permission level I just want all permissions set to allow on that section. 

Thanks in advance
You'd have to create a plugin but you could listen for the entries.saveEntry event that is noted here: http://buildwithcraft.com/docs/plugins/hooks-and-events

Then lookup the value, run validation and even return a custom error message if things were not saved correctly.

Hope this helps.