um: Fix PTRACE_POKEUSER on x86_64

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>

diff --git a/arch/x86/um/ptrace_64.c b/arch/x86/um/ptrace_64.c
index 3b52bf0..b0d25e6 100644 (file)
--- 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, long addr, long data)
        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;