linux-kernel - Re: [PATCH 2/5] gcc-plugins/stackleak: Use asm instrumentation to avoid useless register saving

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Date:   Fri, 12 Jun 2020 02:45:00 +0300
From:   Alexander Popov <alex.popov@...ux.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Emese Revfy <re.emese@...il.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Jessica Yu <jeyu@...nel.org>,
        Sven Schnelle <svens@...ckframe.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Collingbourne <pcc@...gle.com>,
        Naohiro Aota <naohiro.aota@....com>,
        Alexander Monakov <amonakov@...ras.ru>,
        Mathias Krause <minipli@...glemail.com>,
        PaX Team <pageexec@...email.hu>,
        Brad Spengler <spender@...ecurity.net>,
        Laura Abbott <labbott@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        kernel-hardening@...ts.openwall.com, linux-kbuild@...r.kernel.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, gcc@....gnu.org, notify@...nel.org
Subject: Re: [PATCH 2/5] gcc-plugins/stackleak: Use asm instrumentation to
 avoid useless register saving

On 10.06.2020 23:03, Kees Cook wrote:
> On Wed, Jun 10, 2020 at 06:47:14PM +0300, Alexander Popov wrote:
>> On 09.06.2020 21:46, Kees Cook wrote:
>> The inline asm statement that is used for instrumentation is arch-specific.
>> Trying to add
>>   asm volatile("call stackleak_track_stack")
>> in gcc plugin on aarch64 makes gcc break spectacularly.
> 
> Ah! Thank you, that eluded my eyes. :)
> 
>> I pass the target arch name to the plugin and check it explicitly to avoid that.
>>
>> Moreover, I'm going to create a gcc enhancement request for supporting
>> no_caller_saved_registers attribute on aarch64.
> 
> For arm64 right now it looks like the plugin will just remain
> "inefficient" in these cleanup, as before, yes?

Yes, for arm64 the instrumentation didn't change in this patch series.
I checked the disasm and see the similar issue with useless register saving.

I'm going to add asm instrumentation for arm64 when (I hope) the
no_caller_saved_registers attribute becomes available for that platform.

Best regards,
Alexander