Re: [PATCH v2] x86/dumpstack: Fix misleading instruction pointer error message

From: Andy Lutomirski
Date: Mon Nov 16 2020 - 22:29:29 EST


On Mon, Nov 16, 2020 at 3:37 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> On Mon, Nov 16 2020 at 15:04, Andy Lutomirski wrote:
>
> > On Mon, Nov 16, 2020 at 2:01 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> >> arch/x86/kernel/dumpstack.c | 23 +++++++++++++++++++----
> >> 1 file changed, 19 insertions(+), 4 deletions(-)
> >>
> >> --- a/arch/x86/kernel/dumpstack.c
> >> +++ b/arch/x86/kernel/dumpstack.c
> >> @@ -78,6 +78,9 @@ static int copy_code(struct pt_regs *reg
> >> if (!user_mode(regs))
> >> return copy_from_kernel_nofault(buf, (u8 *)src, nbytes);
> >>
> >> + /* The user space code from other tasks cannot be accessed. */
> >> + if (regs != task_pt_regs(current))
> >> + return -EPERM;
> >
> > Depending on exactly where this gets called, this may not be
> > sufficient. You should also check nmi_uaccess_okay().
>
> which is what copy_from_user_nmi() already does.

Whoops. I thought I checked that...