linux-kernel - Re: [uml-devel] [PATCH] um: Fix PTRACE_POKEUSER on x86

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Message-ID: <CAFLxGvxyHYyU8BKb8O3fwd9143VQHLQ-B=+jKc8-2mJGJOGB-Q@mail.gmail.com>
Date:   Wed, 3 May 2017 22:54:33 +0200
From:   Richard Weinberger <richard.weinberger@...il.com>
To:     Richard Weinberger <richard@....at>
Cc:     LKML <linux-kernel@...r.kernel.org>, Jeff Dike <jdike@...toit.com>,
        stable <stable@...r.kernel.org>,
        "user-mode-linux-devel@...ts.sourceforge.net" 
        <user-mode-linux-devel@...ts.sourceforge.net>
Subject: Re: [uml-devel] [PATCH] um: Fix PTRACE_POKEUSER on x86_64

On Sat, Apr 1, 2017 at 12:41 AM, Richard Weinberger <richard@....at> wrote:
> 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.
>
> Cc: <stable@...r.kernel.org>
> Reported-by: jie cao <cj3054@...il.com>
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
>  arch/x86/um/ptrace_64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/um/ptrace_64.c b/arch/x86/um/ptrace_64.c
> index a5c9910d234f..09a085bde0d4 100644
> --- a/arch/x86/um/ptrace_64.c
> +++ b/arch/x86/um/ptrace_64.c
> @@ -125,7 +125,7 @@ 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;

Applied.

-- 
Thanks,
//richard