1. 04 Oct, 2006 1 commit
  2. 10 Jul, 2006 4 commits
  3. 03 Jul, 2006 1 commit
  4. 31 Mar, 2006 1 commit
    • Paolo 'Blaisorblade' Giarrusso's avatar
      [PATCH] uml: clean arch_switch usage · 972410b0
      Paolo 'Blaisorblade' Giarrusso authored
      Call arch_switch also in switch_to_skas, even if it's, for now, a no-op for
      that case (and mark this in the comment); this will change soon.
      Also, arch_switch for TT mode is actually useless when the PT proxy (a
      complicate debugging instrumentation for TT mode) is not enabled.  In fact, it
      only calls update_debugregs, which checks debugregs_seq against seq (to check
      if the registers are up-to-date - seq here means a "version number" of the
      If the ptrace proxy is not enabled, debugregs_seq always stays 0 and
      update_debugregs will be a no-op.  So, optimize this out (the compiler can't
      do it).
      Also, I've been disappointed by the fact that it would make a lot of sense if,
      after calling a successful
      current->thread.arch.debugregs_seq were updated with the new debugregs_seq.
      But this is not done.  Is this a bug or a feature?  For all purposes, it seems
      a bug (otherwise the whole mechanism does not make sense, which is also a
      possibility to check), which causes some performance only problems (not
      correctness), since we write_debugregs when not needed.
      Also, as suggested by Jeff, remove a redundant enabling of SIGVTALRM,
      comprised in the subsequent local_irq_enable().  I'm just a bit dubious if
      ordering matters there...
      Signed-off-by: default avatarPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
      Acked-by: default avatarJeff Dike <jdike@addtoit.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
  5. 01 Feb, 2006 1 commit
  6. 18 Jan, 2006 4 commits
  7. 12 Jan, 2006 2 commits
  8. 08 Jan, 2006 2 commits
  9. 13 Nov, 2005 1 commit
    • Paolo 'Blaisorblade' Giarrusso's avatar
      [PATCH] uml: fix access_ok · 7a590611
      Paolo 'Blaisorblade' Giarrusso authored
      The access_ok_tt() macro is bogus, in that a read access is unconditionally
      considered valid.
      I couldn't find in SCM logs the introduction of this check, but I went back to
      2.4.20-1um and the definition was the same.
      Possibly this was done to avoid problems with missing set_fs() calls, but
      there can't be any I think because they would fail with SKAS mode.
      TT-specific code is still to check.
      Also, this patch joins common code together, and makes the "address range
      wrapping" check happen for all cases, rather than for only some.
      This may, possibly, be reoptimized at some time, but the current code doesn't
      seem clever, just confused.
      * Important: I've also had to change references to access_ok_{tt,skas} back to
        access_ok - the kernel wasn't that happy otherwise.
      Signed-off-by: default avatarPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
      Acked-by: default avatarJeff Dike <jdike@addtoit.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
  10. 07 Nov, 2005 1 commit
  11. 29 Oct, 2005 1 commit
  12. 22 Sep, 2005 1 commit
    • Paolo 'Blaisorblade' Giarrusso's avatar
      [PATCH] uml: fix hang in TT mode on fault · 546fe1cb
      Paolo 'Blaisorblade' Giarrusso authored
      The current code doesn't handle well general protection faults on the host -
      it thinks that cr2 is always the address of a page fault.  While actually, on
      general protection faults, that address is not accessible, so we'd better
      assume we couldn't satisfy the fault.  Currently instead we think we've fixed
      it, so we go back, retry the instruction and fault again endlessly.
      This leads to the kernel hanging when doing copy_from_user(dest, -1, ...) in
      TT mode, since reading *(-1) causes a GFP, and we don't support kernel
      Thanks to Luo Xin for testing UML with LTP and reporting the failures he got.
      Cc: Luo Xin <luothing@sina.com>
      Signed-off-by: default avatarPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
      Cc: Jeff Dike <jdike@addtoit.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
  13. 21 Sep, 2005 2 commits
  14. 17 Sep, 2005 2 commits
  15. 09 Sep, 2005 1 commit
  16. 05 Sep, 2005 3 commits
  17. 07 Jul, 2005 1 commit
    • Jeff Dike's avatar
      [PATCH] uml: skas0 - separate kernel address space on stock hosts · d67b569f
      Jeff Dike authored
      UML has had two modes of operation - an insecure, slow mode (tt mode) in
      which the kernel is mapped into every process address space which requires
      no host kernel modifications, and a secure, faster mode (skas mode) in
      which the UML kernel is in a separate host address space, which requires a
      patch to the host kernel.
      This patch implements something very close to skas mode for hosts which
      don't support skas - I'm calling this skas0.  It provides the security of
      the skas host patch, and some of the performance gains.
      The two main things that are provided by the skas patch, /proc/mm and
      PTRACE_FAULTINFO, are implemented in a way that require no host patch.
      For the remote address space changing stuff (mmap, munmap, and mprotect),
      we set aside two pages in the process above its stack, one of which
      contains a little bit of code which can call mmap et al.
      To update the address space, the system call information (system call
      number and arguments) are written to the stub page above the code.  The
      %esp is set to the beginning of the data, the %eip is set the the start of
      the stub, and it repeatedly pops the information into its registers and
      makes the system call until it sees a system call number of zero.  This is
      to amortize the cost of the context switch across multiple address space
      When the updates are done, it SIGSTOPs itself, and the kernel process
      continues what it was doing.
      For a PTRACE_FAULTINFO replacement, we set up a SIGSEGV handler in the
      child, and let it handle segfaults rather than nullifying them.  The
      handler is in the same page as the mmap stub.  The second page is used as
      the stack.  The handler reads cr2 and err from the sigcontext, sticks them
      at the base of the stack in a faultinfo struct, and SIGSTOPs itself.  The
      kernel then reads the faultinfo and handles the fault.
      A complication on x86_64 is that this involves resetting the registers to
      the segfault values when the process is inside the kill system call.  This
      breaks on x86_64 because %rcx will contain %rip because you tell SYSRET
      where to return to by putting the value in %rcx.  So, this corrupts $rcx on
      return from the segfault.  To work around this, I added an
      arch_finish_segv, which on x86 does nothing, but which on x86_64 ptraces
      the child back through the sigreturn.  This causes %rcx to be restored by
      sigreturn and avoids the corruption.  Ultimately, I think I will replace
      this with the trick of having it send itself a blocked signal which will be
      unblocked by the sigreturn.  This will allow it to be stopped just after
      the sigreturn, and PTRACE_SYSCALLed without all the back-and-forth of
      PTRACE_SYSCALLing it through sigreturn.
      This runs on a stock host, so theoretically (and hopefully), tt mode isn't
      needed any more.  We need to make sure that this is better in every way
      than tt mode, though.  I'm concerned about the speed of address space
      updates and page fault handling, since they involve extra round-trips to
      the child.  We can amortize the round-trip cost for large address space
      updates by writing all of the operations to the data page and having the
      child execute them all at the same time.  This will help fork and exec, but
      not page faults, since they involve only one page.
      I can't think of any way to help page faults, except to add something like
      PTRACE_FAULTINFO to the host.  There is PTRACE_SIGINFO, but UML doesn't use
      siginfo for SIGSEGV (or anything else) because there isn't enough
      information in the siginfo struct to handle page faults (the faulting
      operation type is missing).  Adding that would make PTRACE_SIGINFO a usable
      equivalent to PTRACE_FAULTINFO.
      As for the code itself:
      - The system call stub is in arch/um/kernel/sys-$(SUBARCH)/stub.S.  It is
        put in its own section of the binary along with stub_segv_handler in
        arch/um/kernel/skas/process.c.  This is manipulated with run_syscall_stub
        in arch/um/kernel/skas/mem_user.c.  syscall_stub will execute any system
        call at all, but it's only used for mmap, munmap, and mprotect.
      - The x86_64 stub calls sigreturn by hand rather than allowing the normal
        sigreturn to happen, because the normal sigreturn is a SA_RESTORER in
        UML's address space provided by libc.  Needless to say, this is not
        available in the child's address space.  Also, it does a couple of odd
        pops before that which restore the stack to the state it was in at the
        time the signal handler was called.
      - There is a new field in the arch mmu_context, which is now a union.
        This is the pid to be manipulated rather than the /proc/mm file
        descriptor.  Code which deals with this now checks proc_mm to see whether
        it should use the usual skas code or the new code.
      - userspace_tramp is now used to create a new host process for every UML
        process, rather than one per UML processor.  It checks proc_mm and
        ptrace_faultinfo to decide whether to map in the pages above its stack.
      - start_userspace now makes CLONE_VM conditional on proc_mm since we need
        separate address spaces now.
      - switch_mm_skas now just sets userspace_pid[0] to the new pid rather
        than PTRACE_SWITCH_MM.  There is an addition to userspace which updates
        its idea of the pid being manipulated each time around the loop.  This is
        important on exec, when the pid will change underneath userspace().
      - The stub page has a pte, but it can't be mapped in using tlb_flush
        because it is part of tlb_flush.  This is why it's required for it to be
        mapped in by userspace_tramp.
      Other random things:
      - The stub section in uml.lds.S is page aligned.  This page is written
        out to the backing vm file in setup_physmem because it is mapped from
        there into user processes.
      - There's some confusion with TASK_SIZE now that there are a couple of
        extra pages that the process can't use.  TASK_SIZE is considered by the
        elf code to be the usable process memory, which is reasonable, so it is
        decreased by two pages.  This confuses the definition of
        USER_PGDS_IN_LAST_PML4, making it too small because of the rounding down
        of the uneven division.  So we round it to the nearest PGDIR_SIZE rather
        than the lower one.
      - I added a missing PT_SYSCALL_ARG6_OFFSET macro.
      - um_mmu.h was made into a userspace-usable file.
      - proc_mm and ptrace_faultinfo are globals which say whether the host
        supports these features.
      - There is a bad interaction between the mm.nr_ptes check at the end of
        exit_mmap, stack randomization, and skas0.  exit_mmap will stop freeing
        pages at the PGDIR_SIZE boundary after the last vma.  If the stack isn't
        on the last page table page, the last pte page won't be freed, as it
        should be since the stub ptes are there, and exit_mmap will BUG because
        there is an unfreed page.  To get around this, TASK_SIZE is set to the
        next lowest PGDIR_SIZE boundary and mm->nr_ptes is decremented after the
        calls to init_stub_pte.  This ensures that we know the process stack (and
        all other process mappings) will be below the top page table page, and
        thus we know that mm->nr_ptes will be one too many, and can be
      Things that need fixing:
      - We may need better assurrences that the stub code is PIC.
      - The stub pte is set up in init_new_context_skas.
      - alloc_pgdir is probably the right place.
      Signed-off-by: default avatarJeff Dike <jdike@addtoit.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
  18. 25 Jun, 2005 3 commits
  19. 21 Jun, 2005 1 commit
  20. 28 May, 2005 1 commit
  21. 20 May, 2005 1 commit
  22. 06 May, 2005 4 commits
  23. 05 May, 2005 1 commit