• Chuck Ebbert's avatar
    x86 - 32-bit ptrace emulation mishandles 6th arg · ecd744ee
    Chuck Ebbert authored
    [ jdike - Pushing Chuck's patch - see
    http://lkml.org/lkml/2005/9/16/261 for some history and a test
    program.  UML is also broken without this patch - its processes get
    SIGBUS from the corrupt 6th argument to mmap being interpretted as a
    file offset ]
    
    When the 32-bit vDSO is used to make a system call, the %ebp register for
    the 6th syscall arg has to be loaded from the user stack (where it's pushed
    by the vDSO user code).  The native i386 kernel always does this before
    stopping for syscall tracing, so %ebp can be seen and modified via ptrace
    to access the 6th syscall argument.  The x86-64 kernel fails to do this,
    presenting the stack address to ptrace instead.  This makes the %rbp value
    seen by 64-bit ptrace of a 32-bit process, and the %ebp value seen by a
    32-bit caller of ptrace, both differ from the native i386 behavior.
    
    This patch fixes the problem by putting the word loaded from the user stack
    into %rbp before calling syscall_trace_enter, and reloading the 6th syscall
    argument from there afterwards (so ptrace can change it).  This makes the
    behavior match that of i386 kernels.
    Original-Patch-By: default avatarRoland McGrath <roland@redhat.com>
    Signed-off-by: default avatarChuck Ebbert <76306.1226@compuserve.com>
    Signed-off-by: default avatarJeff Dike <jdike@linux.intel.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    ecd744ee
ia32entry.S 18.4 KB