-(* The implementation of 'ps' has gone through a number of complete
- * rewrites. This explains the "leading theories" of how to implement
- * this. Probably some sort of hybrid method is the way to go.
- *
- * General comments: The init_task ksym points to the initial
- * task_struct (PID 0, swapper). Out from this init task_struct
- * we find linked lists (struct list_head) which cover all
- * tasks and subsets of the tasks (eg. parent/children).
- * So if we have init_task and we know what the task_struct
- * looks like, then we can follow these chains of pointers
- * to find all processes in the kernel.
- *
- * task_struct varies greatly depending on: word size, kernel
- * version, CONFIG_* settings, and vendor/additional patches.
- *
- * (Theory 1) Precompiled task_struct. We can easily and reliably
- * determine the Linux kernel version (see virt-uname). In
- * theory we could compile a list of known kernel versions,
- * check out their sources beforehand, and find the absolute
- * layout of the task_struct (eg. using CIL). This method would
- * only work for known kernel versions, but has the advantage
- * that all fields in the task_struct would be known.
- *
- * (Theory 2) Fuzzy matched task_struct. The task_struct has
- * a certain internal structure which is stable even over many
- * kernel revisions. For example, groups of pointers always
- * occur together. We search through init_task looking for
- * these characteristic features and where a pointer is found
- * to another task_struct we search that (recursively) on the
- * assumption that those contain the same features at the same
- * location. This works well for pointers, but not so well for
- * finding other fields (eg. uids, process name, etc). We can
- * defray the cost of searches by caching the results between
- * runs.
- *)
-
-(* This accumulator stores a map of task_struct address to
- * task_struct content. It can also store the address of a
- * task_struct which isn't fully parsed yet.
- * key: address (int64)
- * value: task_struct option (None if not parsed yet)
- *)
-type task_struct = {
- ts_addr : int64;
-}
-
-module Accum = struct
- include Map.Make (Int64)
-
- let contains_addr accum addr = mem addr accum
- let add_address accum addr = add addr None accum
- let add_task_struct accum addr ts = add addr (Some ts) accum
-end
-
-exception ShapeError of int
-
-(* Parse (recursively) all task_structs, starting at init_task.
- *
- * Either returns an accumulator of task_structs, or raises an
- * exception.
- *
- * On failure, the caller can try again with a different shape.
- * The exception gives some information back to the caller about
- * where the match failed, allowing faster, directed searches.
- *)
-let get_task_struct debug mem ((ws,e) as wse) ((n1,n2) as shape)
- addr accum =
-
- (* The 'struct list_head', the standard double-linked list used
- * by Linux, contains next and prev pointers. However these point
- * not to the beginning of the struct, but to the offset of the
- * list_head within the struct. This function adjusts the pointer
- * to get back to the beginning of the struct.
- *)
- let container_of addr bitoffset =
- if addr <> 0L then (
- let offset = Int64.of_int (bitoffset lsr 3) in
- addr -^ offset
- ) else 0L
- in
-
- (* Do get_task_struct as a recursive subfunction so we don't have
- * to pass around all the fixed arguments on the stack.
- *)
- let rec get_task_struct ~i addr accum =
- if Accum.contains_addr accum addr then accum
- else (
- (* NOTE: The order of the following three statements is crucial
- * to avoid cycles and malicious guests. Do not change it!
- *)
- let bits =
- try Bitstring.bitstring_of_string (get_bytes mem addr (4096*8))
- with Invalid_argument "get_bytes" -> raise (ShapeError i) in
- let accum = Accum.add_address accum addr in
- let accum = ref accum in
-
- if debug then
- eprintf "trying to match task_struct, i=%d %Lx\n%!" i addr;
-
- bitmatch bits with
- | { _ : n1*ws : bitstring; (* Ignore start of task_struct. *)
-
- (* struct list_head tasks *)
- tasks_next : ws : endian(e),
- save_offset_to (offset),
- bind (let addr = container_of tasks_next offset in
- eprintf "offset = %d, tasks_next = %Lx, addr = %Lx\n"
- offset tasks_next addr;
- accum := get_task_struct ~i:1 addr !accum;
- addr);
- tasks_prev : ws : endian(e),
- bind (let addr = container_of tasks_prev offset in
- eprintf "offset = %d, tasks_prev = %Lx, addr = %Lx\n"
- offset tasks_prev addr;
- accum := get_task_struct ~i:1 addr !accum;
- addr);
-
- _ : n2*ws : bitstring;
-
- (* struct task_struct *parent *)
- parent : ws : endian(e),
- bind (let addr = parent in
- accum := get_task_struct ~i:2 addr !accum;
- addr);
-
- (* struct list_head children *)
- children_next : ws : endian(e),
- save_offset_to (offset),
- bind (let addr = container_of children_next offset in
- accum := get_task_struct ~i:2 addr !accum;
- addr);
-
- children_prev : ws : endian(e),
- bind (let addr = container_of children_prev offset in
- accum := get_task_struct ~i:2 addr !accum;
- addr);
-
- (* struct list_head sibling *)
- sibling_next : ws : endian(e),
- save_offset_to (offset),
- bind (let addr = container_of sibling_next offset in
- accum := get_task_struct ~i:2 addr !accum;
- addr);
-
- sibling_prev : ws : endian(e),
- bind (let addr = container_of sibling_prev offset in
- accum := get_task_struct ~i:2 addr !accum;
- addr);
-
- (* struct task_struct *group_leader *)
- group_leader : ws : endian(e),
- bind (let addr = group_leader in
- accum := get_task_struct ~i:2 addr !accum;
- addr)
- } ->
- (* Successful match, so return the updated accumulator. *)
- let accum = !accum in
- let accum = Accum.add_task_struct accum addr { ts_addr = addr } in
- accum
-
- | { _ } ->
- (* Unsuccessful match, throw an exception. *)
- raise (ShapeError (-1))
- )
- in
- get_task_struct ~i:0 addr accum
-
-(* This is the directed search function. *)
-let search debug mem ksymmap =
- let ws = get_wordsize mem in
- let ws = match ws with W32 -> 32 | W64 -> 64 in
- let e = get_endian mem in
- let wse = ws, e in
-
- let init_task =
- try Ksymmap.find "init_task" ksymmap
- with Not_found ->
- eprintf "virt-ps: cannot find kernel symbol 'init_task'\n";
- exit 1 in
-
- let accum = Accum.empty in
-
- let rec loop n1 n2 =
- try
- if debug then eprintf "search: trying (%d, %d)\n" n1 n2;
- let ts = get_task_struct debug mem wse (n1, n2) init_task accum in
- if debug then eprintf "search: success (%d, %d)\n" n1 n2;
- ts
- with
- | ShapeError ((-1|0|1) as i) ->
- if debug then eprintf "search: ShapeError %d\n" i;
- loop (n1+1) n2
- | ShapeError 2 ->
- if debug then eprintf "search: ShapeError 2\n";
- loop n1 (n2+1)
- in
- let ts = loop 0 0 in
- ()
git.annexia.org / virt-mem.git / commitdiff