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userspace: allow thread IDs to be re-used

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It's currently too easy to run out of thread IDs as they
are never re-used on thread exit.

Now the kernel maintains a bitfield of in-use thread IDs,
updated on thread creation and termination. When a thread
exits, the permission bitfield for all kernel objects is
updated to revoke access for that retired thread ID, so that
a new thread re-using that ID will not gain access to objects
that it should not have.

Because of these runtime updates, setting the permission
bitmap for an object to all ones for a "public" object doesn't
work properly any more; a flag is now set for this instead.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2017-10-13 13:57:07 -07:00 • committed by Andrew Boie
commit 04caa679c9
7 changed files with 97 additions and 20 deletions
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4
include/kernel.h
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@ -180,6 +180,7 @@ struct _k_object {
} __packed;
#define K_OBJ_FLAG_INITIALIZED BIT(0)
#define K_OBJ_FLAG_PUBLIC BIT(1)
/**
* Lookup a kernel object and init its metadata if it exists
@ -253,6 +254,9 @@ __syscall void k_object_access_revoke(void *object, struct k_thread *thread);
* as it is possible for such code to derive the addresses of kernel objects
* and perform unwanted operations on them.
*
* It is not possible to revoke permissions on public objects; once public,
* any thread may use it.
*
* @param object Address of kernel object
*/
__syscall void k_object_access_all_grant(void *object);