linux-kernel - Re: [bzImage64_load] BUG: KASAN: stack-out-of-bounds in deref_stack

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Message-ID: <20171107172401.tmjllqfnkqxvq3x4@treble>
Date:   Tue, 7 Nov 2017 11:24:01 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Fengguang Wu <fengguang.wu@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [bzImage64_load] BUG: KASAN: stack-out-of-bounds in
 deref_stack_reg+0xb5/0x11a

On Tue, Nov 07, 2017 at 08:32:19AM -0800, Linus Torvalds wrote:
> On Tue, Nov 7, 2017 at 1:32 AM, Fengguang Wu <fengguang.wu@...el.com> wrote:
> >
> > [    7.795097] Kprobe smoke test: started
> > [    7.807563] ==================================================================
> > [    7.808007] BUG: KASAN: stack-out-of-bounds in deref_stack_reg+0xb5/0x11a
> 
> Ok, this is apparently with a new enough gcc to make it valid: gcc
> version 6.2.0.
> 
> Adding Josh to the list of people, since it's in the unwinder. Josh,
> I'll forward the original report with full dmesg and config in
> private.

It looks like the unwinder got confused because of a kprobe breakpoint
at the beginning of the kprobe_target() function.

At least it only read a bad address *on* the stack.  It didn't go off
beyond the stack -- it has safeguards for that.

I don't think there's a good solution for this, unless we had some kind
of unwinder integration with generated/patched code.

I think I'll just have to disable KASAN warnings in the ORC code.

-- 
Josh