linux-kernel - Re: [PATCH 1/3] arm64: kprobes: Move extable address check into arch_prepare

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Date:   Tue, 15 Jan 2019 14:49:55 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     James Morse <james.morse@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Pratyush Anand <panand@...hat.com>,
        "David A . Long" <dave.long@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] arm64: kprobes: Move extable address check into
 arch_prepare_kprobe()

On Fri, 11 Jan 2019 18:22:38 +0000
James Morse <james.morse@....com> wrote:

> Hi,
> 
> On 09/01/2019 02:05, Masami Hiramatsu wrote:
> > On Tue, 8 Jan 2019 17:13:36 +0000
> > James Morse <james.morse@....com> wrote:
> >> On 08/01/2019 02:39, Masami Hiramatsu wrote:
> >>> On Thu, 3 Jan 2019 17:05:18 +0000
> >>> James Morse <james.morse@....com> wrote:
> >>>> On 17/12/2018 06:40, Masami Hiramatsu wrote:
> >>>>> Move extable address check into arch_prepare_kprobe() from
> >>>>> arch_within_kprobe_blacklist().
> >>>>
> >>>> I'm trying to work out the pattern for what should go in the blacklist, and what
> >>>> should be rejected by the arch code.
> >>>>
> >>>> It seems address-ranges should be blacklisted as the contents don't matter.
> >>>> easy-example: the idmap text.
> >>>
> >>> Yes, more precisely, the code smaller than a function (symbol), it must be
> >>> rejected by arch_prepare_kprobe(), since blacklist is poplated based on
> >>> kallsyms.
> >>
> >> Ah, okay, so the pattern is the blacklist should only be for whole symbols,
> >> (which explains why its usually based on sections).
> > 
> > Correct. Actually, the blacklist is generated based on the symbol info
> > from symbol address.
> > 
> >> I see kprobe_add_ksym_blacklist() would go wrong if you give it something like:
> >> platform_drv_probe+0x50/0xb0, as it will log platform_drv_probe+0x50 as the
> >> start_addr and platform_drv_probe+0x50+0xb0 as the end.
> > 
> > Yes, it expects given address is the entry of a symbol.
> 
> >> But how does anything from the arch code's blacklist get into the
> >> kprobe_blacklist list?
> > 
> > It should be done via arch_populate_kprobe_blacklist().
> 
> >> We don't have an arch_populate_kprobe_blacklist(), so rely on
> >> within_kprobe_blacklist() calling arch_within_kprobe_blacklist() with the
> >> address, as well as walking kprobe_blacklist.
> >>
> >> Is this cleanup ahead of a series that does away with
> >> arch_within_kprobe_blacklist() so that debugfs list is always complete?
> > 
> > Right, after this cleanup, I will send arch_populate_kprobe_blacklist()
> > patch for arm64 and others. My plan is to move all arch_within_kprobe_blacklist()
> > to arch_populate_kprobe_blacklist() so that user can get more precise blacklist
> > via debugfs.
> 
> Thanks, now it all makes sense!
> 
> Reviewed-by: James Morse <james.morse@....com>

Thanks!

> 
> 
> Could you include a paragraph like that in the cover-letter or commit-message?
> The 'fix' in the cover-letter subject had me looking for the bug!

Ok, I'll update commit message with your reviewed-by.

Thank you!

> 
> 
> Thanks,
> 
> James


-- 
Masami Hiramatsu <mhiramat@...nel.org>