From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org
X-Spam-Level: 
X-Spam-Status: No, score=-3.8 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,
	RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no
	version=3.4.4
Received: (qmail 4066 invoked from network); 2 Jun 2021 16:03:19 -0000
Received: from mother.openwall.net (195.42.179.200)
  by inbox.vuxu.org with ESMTPUTF8; 2 Jun 2021 16:03:19 -0000
Received: (qmail 28202 invoked by uid 550); 2 Jun 2021 16:03:17 -0000
Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm
Precedence: bulk
List-Post: <mailto:musl@lists.openwall.com>
List-Help: <mailto:musl-help@lists.openwall.com>
List-Unsubscribe: <mailto:musl-unsubscribe@lists.openwall.com>
List-Subscribe: <mailto:musl-subscribe@lists.openwall.com>
List-ID: <musl.lists.openwall.com>
Reply-To: musl@lists.openwall.com
Received: (qmail 28181 invoked from network); 2 Jun 2021 16:03:16 -0000
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
	s=k20201202; t=1622649784;
	bh=+3X9i94DZvJYL7wDLo1sRTEb1ToSfJ8tKeEf+y9M5h0=;
	h=References:In-Reply-To:From:Date:Subject:To:Cc:From;
	b=NLPw6HfuWH2aw7rLGwHO7m9uk282jK0AU6vinGYTx1BOnvJTxdxRpffBEdBGAeebM
	 e5RSsEgrYaG9Gx1uoknDISLE0Sm4kOJ6Ns15XBnZTECyvbq6B/3C3xUUC2h+bV4G7Q
	 8hFyPtq9oNwDTGg+yNKG7ZYK36jWS2hLoyB7JArC78ameQGpDw0bSYh5IAtr2fbF8b
	 u+np11slI/3WHGcaUFMyJQwVF28ToX71zusvAxtzW2Vdl80qnG9jlUe12qp4u8xE/T
	 7N4EYXNLtHlYETLDGNqrNNXlZfYfBB2Q6iUtJteFLBLOO7vZ45NSeH5Rj3IVdmhjks
	 El+zKftXZoWHA==
X-Gm-Message-State: AOAM5309XERn1eMYRylD+EwURpj0dO2erFtTvTGaryHMr/alvYCJa9JB
	4tVVGmsJEpsjRHUt8A3uZYYeQbY1ZinXTasIyFM=
X-Google-Smtp-Source: ABdhPJzgAtYTyAUZe477Q4d1tUxrB3J/lqoj4TNwhwzcGLRyS6PWAiDbhwBPED9D2Z1U/qY6z4o+lTpbQCGapFm8G54=
X-Received: by 2002:a9d:6186:: with SMTP id g6mr11777811otk.246.1622649783524;
 Wed, 02 Jun 2021 09:03:03 -0700 (PDT)
MIME-Version: 1.0
References: <CAHHiRUQ_aFObcofofa1zTdDyWuM+ZO5F0Gb50SAsZnPxKErSjw@mail.gmail.com>
 <20210510185837.GD2031@voyager> <CAHHiRUQ8uh5_EY8eLyq3C1S=NLHjW9ytsDKk9mVTJ1k1j37ypg@mail.gmail.com>
 <20210524220004.GD2546@brightrain.aerifal.cx> <CAHHiRURfq=gY1jmoek1v7=hOayK3u51c7tgR-G24F5S50gptmA@mail.gmail.com>
 <CAK8P3a2MDvXCQGbjcUiXZko8yWgn+r1Gc0G6ajYG08m41ibY8g@mail.gmail.com> <20210602145632.GC13220@brightrain.aerifal.cx>
In-Reply-To: <20210602145632.GC13220@brightrain.aerifal.cx>
From: Arnd Bergmann <arnd@kernel.org>
Date: Wed, 2 Jun 2021 18:01:24 +0200
X-Gmail-Original-Message-ID: <CAK8P3a1ADtyVkY8zWd=6KhJLR4eWpyfvDuZMzc_EKp4szC_y7Q@mail.gmail.com>
Message-ID: <CAK8P3a1ADtyVkY8zWd=6KhJLR4eWpyfvDuZMzc_EKp4szC_y7Q@mail.gmail.com>
To: musl@lists.openwall.com
Cc: Markus Wichmann <nullplan@gmx.net>, Florian Weimer <fweimer@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Subject: Re: [musl] Backwards kernel compatibility

On Wed, Jun 2, 2021 at 4:56 PM Rich Felker <dalias@libc.org> wrote:
> On Wed, Jun 02, 2021 at 01:52:43PM +0200, Arnd Bergmann wrote:
> > >
> > > The main source of overhead comes from the kernel 4.4 which on arm64
> > > produces stack traces when not implemented syscall is invoked:
> > >
> > >     https://github.com/torvalds/linux/blob/afd2ff9b7e1b367172f18ba7f693dfb62bdcb2dc/arch/arm64/kernel/traps.c#L369
> >
> > That is clearly a bug that was fixed in mainline and backported to linux-4.14
> > but not 4.4 or 4.9. I've sent a manual backport for inclusion in those kernels
> > now.
>
> Is this practical to hotpatch into kernels on devices that aren't
> readily upgradable?

Including the patch in a source tree is trivial, as it just removes a few lines
of (misguided) output. If you are asking about run-time patching it out of
a running kernel using kpatch/kGraft/ksplice, this would also be doable
by patching out the branch in that function, but the infrastructure for live
patching kernels is likely missing on most of the systems that lack a way to
replace the kernel image, so in practice it would not help.

       Arnd