linux-kernel - Re: [PATCH 5/5] arm64: Add uprobe support

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Date:   Wed, 28 Sep 2016 18:12:10 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Pratyush Anand <panand@...hat.com>
Cc:     Mark Rutland <mark.rutland@....com>, srikar@...ux.vnet.ibm.com,
        Will Deacon <will.deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Jungseok Lee <jungseoklee85@...il.com>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        vijaya.kumar@...iumnetworks.com, Dave Long <dave.long@...aro.org>,
        Shi Yang <yang.shi@...aro.org>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Steve Capper <steve.capper@...aro.org>,
        "Suzuki K. Poulose" <suzuki.poulose@....com>,
        Andre Przywara <andre.przywara@....com>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Ashok Kumar <ashoks@...adcom.com>,
        Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
        Will Cohen <wcohen@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        open list <linux-kernel@...r.kernel.org>,
        James Morse <james.morse@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 5/5] arm64: Add uprobe support

On Tue, Sep 27, 2016 at 08:33:25PM +0530, Pratyush Anand wrote:
> On Tuesday 27 September 2016 07:21 PM, Catalin Marinas wrote:
> >There is also the is_trap_at_addr() function which uses is_trap_insn().
> >I haven't checked the call paths here, are there any implications if
> >is_trap_insn() always returns false?
> 
> I had looked into it and also tested that a tracepoint at an application
> having a same instruction as that of "uprobe break instruction" ie "BRK
> #0x5" is rejected. So, I think a false positive return from is_tarp_insn()
> is still OK.

Looking at handle_swbp(), if we hit a breakpoint for which we don't have
a valid uprobe, this function currently sends a SIGTRAP. But if
is_trap_insn() returns false always, is_trap_at_addr() would return 0 in
this case so the SIGTRAP is never issued.

-- 
Catalin