On Fri, 02 Jan 2015 07:50:55 +0530, me storage said: > Can any one please tell me difference between kernal space & user space in > code perspective
Two biggies: 1) Kernel space pages are usually nailed down and not paging in and out, this is *not* true for userspace pages (so special tap-dancing in copy_(to/from)_user() is needed to make sure no page faults happen). 2) Data inside the kernel can usually be trusted from a security standpoint. Data in userspace *MUST NOT* be trusted. Also, beware of TOCTOU (time of check / time of use) bugs - that's why we should copy the user-supplied data to an internal buffer *first*, and then validity-check the buffer - if we check the value in userspace and then later copy it, there's a race condition where the userspace value can be changed after the check but before the copy. Also, keep in mind that a userspace pointer needs to be translated before using it to dereference data from kernel space....
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