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

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Message-ID: <878sb0yisp.fsf@nanos.tec.linutronix.de>
Date:   Tue, 17 Nov 2020 00:37:58 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Borislav Petkov <bp@...en8.de>, Oleg Nesterov <oleg@...hat.com>,
        Mark Mossberg <mark.mossberg@...il.com>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jann Horn <jannh@...gle.com>,
        kyin@...hat.com
Subject: Re: [PATCH v2] x86/dumpstack: Fix misleading instruction pointer error message

On Mon, Nov 16 2020 at 15:04, Andy Lutomirski wrote:

> On Mon, Nov 16, 2020 at 2:01 PM Thomas Gleixner <tglx@...utronix.de> 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.