• Srikar Dronamraju's avatar
    uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints · 2b144498
    Srikar Dronamraju authored
    Add uprobes support to the core kernel, with x86 support.
    
    This commit adds the kernel facilities, the actual uprobes
    user-space ABI and perf probe support comes in later commits.
    
    General design:
    
    Uprobes are maintained in an rb-tree indexed by inode and offset
    (the offset here is from the start of the mapping). For a unique
    (inode, offset) tuple, there can be at most one uprobe in the
    rb-tree.
    
    Since the (inode, offset) tuple identifies a unique uprobe, more
    than one user may be interested in the same uprobe. This provides
    the ability to connect multiple 'consumers' to the same uprobe.
    
    Each consumer defines a handler and a filter (optional). The
    'handler' is run every time the uprobe is hit, if it matches the
    'filter' criteria.
    
    The first consumer of a uprobe causes the breakpoint to be
    inserted at the specified address and subsequent consumers are
    appended to this list.  On subsequent probes, the consumer gets
    appended to the existing list of consumers. The breakpoint is
    removed when the last consumer unregisters. For all other
    unregisterations, the consumer is removed from the list of
    consumers.
    
    Given a inode, we get a list of the mms that have mapped the
    inode. Do the actual registration if mm maps the page where a
    probe needs to be inserted/removed.
    
    We use a temporary list to walk through the vmas that map the
    inode.
    
    - The number of maps that map the inode, is not known before we
      walk the rmap and keeps changing.
    - extending vm_area_struct wasn't recommended, it's a
      size-critical data structure.
    - There can be more than one maps of the inode in the same mm.
    
    We add callbacks to the mmap methods to keep an eye on text vmas
    that are of interest to uprobes.  When a vma of interest is mapped,
    we insert the breakpoint at the right address.
    
    Uprobe works by replacing the instruction at the address defined
    by (inode, offset) with the arch specific breakpoint
    instruction. We save a copy of the original instruction at the
    uprobed address.
    
    This is needed for:
    
     a. executing the instruction out-of-line (xol).
     b. instruction analysis for any subsequent fixups.
     c. restoring the instruction back when the uprobe is unregistered.
    
    We insert or delete a breakpoint instruction, and this
    breakpoint instruction is assumed to be the smallest instruction
    available on the platform. For fixed size instruction platforms
    this is trivially true, for variable size instruction platforms
    the breakpoint instruction is typically the smallest (often a
    single byte).
    
    Writing the instruction is done by COWing the page and changing
    the instruction during the copy, this even though most platforms
    allow atomic writes of the breakpoint instruction. This also
    mirrors the behaviour of a ptrace() memory write to a PRIVATE
    file map.
    
    The core worker is derived from KSM's replace_page() logic.
    
    In essence, similar to KSM:
    
     a. allocate a new page and copy over contents of the page that
        has the uprobed vaddr
     b. modify the copy and insert the breakpoint at the required
        address
     c. switch the original page with the copy containing the
        breakpoint
     d. flush page tables.
    
    replace_page() is being replicated here because of some minor
    changes in the type of pages and also because Hugh Dickins had
    plans to improve replace_page() for KSM specific work.
    
    Instruction analysis on x86 is based on instruction decoder and
    determines if an instruction can be probed and determines the
    necessary fixups after singlestep.  Instruction analysis is done
    at probe insertion time so that we avoid having to repeat the
    same analysis every time a probe is hit.
    
    A lot of code here is due to the improvement/suggestions/inputs
    from Peter Zijlstra.
    
    Changelog:
    
    (v10):
     - Add code to clear REX.B prefix as suggested by Denys Vlasenko
       and Masami Hiramatsu.
    
    (v9):
     - Use insn_offset_modrm as suggested by Masami Hiramatsu.
    
    (v7):
    
     Handle comments from Peter Zijlstra:
    
     - Dont take reference to inode. (expect inode to uprobe_register to be sane).
     - Use PTR_ERR to set the return value.
     - No need to take reference to inode.
     - use PTR_ERR to return error value.
     - register and uprobe_unregister share code.
    
    (v5):
    
     - Modified del_consumer as per comments from Peter.
     - Drop reference to inode before dropping reference to uprobe.
     - Use i_size_read(inode) instead of inode->i_size.
     - Ensure uprobe->consumers is NULL, before __uprobe_unregister() is called.
     - Includes errno.h as recommended by Stephen Rothwell to fix a build issue
       on sparc defconfig
     - Remove restrictions while unregistering.
     - Earlier code leaked inode references under some conditions while
       registering/unregistering.
     - Continue the vma-rmap walk even if the intermediate vma doesnt
       meet the requirements.
     - Validate the vma found by find_vma before inserting/removing the
       breakpoint
     - Call del_consumer under mutex_lock.
     - Use hash locks.
     - Handle mremap.
     - Introduce find_least_offset_node() instead of close match logic in
       find_uprobe
     - Uprobes no more depends on MM_OWNER; No reference to task_structs
       while inserting/removing a probe.
     - Uses read_mapping_page instead of grab_cache_page so that the pages
       have valid content.
     - pass NULL to get_user_pages for the task parameter.
     - call SetPageUptodate on the new page allocated in write_opcode.
     - fix leaking a reference to the new page under certain conditions.
     - Include Instruction Decoder if Uprobes gets defined.
     - Remove const attributes for instruction prefix arrays.
     - Uses mm_context to know if the application is 32 bit.
    Signed-off-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
    Also-written-by: default avatarJim Keniston <jkenisto@us.ibm.com>
    Reviewed-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Roland McGrath <roland@hack.frob.com>
    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
    Cc: Anton Arapov <anton@redhat.com>
    Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    Cc: Stephen Rothwell <sfr@canb.auug.org.au>
    Cc: Denys Vlasenko <vda.linux@googlemail.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linux-mm <linux-mm@kvack.org>
    Link: http://lkml.kernel.org/r/20120209092642.GE16600@linux.vnet.ibm.com
    [ Made various small edits to the commit log ]
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    2b144498
uprobes.h 1.29 KB