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    Subject[PATCH 3.16 112/134] um: Fix PTRACE_POKEUSER on x86_64
    3.16.47-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Richard Weinberger <richard@nod.at>

    commit 9abc74a22d85ab29cef9896a2582a530da7e79bf upstream.

    This is broken since ever but sadly nobody noticed.
    Recent versions of GDB set DR_CONTROL unconditionally and
    UML dies due to a heap corruption. It turns out that
    the PTRACE_POKEUSER was copy&pasted from i386 and assumes
    that addresses are 4 bytes long.

    Fix that by using 8 as address size in the calculation.

    Reported-by: jie cao <cj3054@gmail.com>
    Signed-off-by: Richard Weinberger <richard@nod.at>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    arch/x86/um/ptrace_64.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/x86/um/ptrace_64.c
    +++ b/arch/x86/um/ptrace_64.c
    @@ -120,7 +120,7 @@ int poke_user(struct task_struct *child,
    else if ((addr >= offsetof(struct user, u_debugreg[0])) &&
    (addr <= offsetof(struct user, u_debugreg[7]))) {
    addr -= offsetof(struct user, u_debugreg[0]);
    - addr = addr >> 2;
    + addr = addr >> 3;
    if ((addr == 4) || (addr == 5))
    return -EIO;
    child->thread.arch.debugregs[addr] = data;
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