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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id p1-20020a17090a680100b001d28905b214sm22614pjj.39.2022.04.20.10.47.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Apr 2022 10:47:40 -0700 (PDT) Date: Wed, 20 Apr 2022 10:47:39 -0700 From: Kees Cook To: Rich Felker Cc: Palmer Dabbelt , ebiederm@xmission.com, damien.lemoal@opensource.wdc.com, Niklas.Cassel@wdc.com, viro@zeniv.linux.org.uk, Paul Walmsley , aou@eecs.berkeley.edu, vapier@gentoo.org, stable@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, geert@linux-m68k.org, linux-m68k@lists.linux-m68k.org, gerg@linux-m68k.org, linux-arm-kernel@lists.infradead.org, linux-sh@vger.kernel.org, ysato@users.sourceforge.jp Subject: Re: [PATCH] binfmt_flat: Remove shared library support Message-ID: <202204201044.ACFEB0C@keescook> References: <87levzzts4.fsf_-_@email.froward.int.ebiederm.org> <20220420165935.GA12207@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220420165935.GA12207@brightrain.aerifal.cx> X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 951264001E X-Stat-Signature: 3zg34bw9tpshrtypmz5cugtwtcaz4khz Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=ifQm0MVg; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf04.hostedemail.com: domain of keescook@chromium.org designates 209.85.210.180 as permitted sender) smtp.mailfrom=keescook@chromium.org X-HE-Tag: 1650476860-857871 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Apr 20, 2022 at 12:59:37PM -0400, Rich Felker wrote: > On Wed, Apr 20, 2022 at 09:17:22AM -0700, Palmer Dabbelt wrote: > > On Wed, 20 Apr 2022 07:58:03 PDT (-0700), ebiederm@xmission.com wrote: > > > > > >In a recent discussion[1] it was reported that the binfmt_flat library > > >support was only ever used on m68k and even on m68k has not been used > > >in a very long time. > > > > > >The structure of binfmt_flat is different from all of the other binfmt > > >implementations becasue of this shared library support and it made > > >life and code review more effort when I refactored the code in fs/exec.c. > > > > > >Since in practice the code is dead remove the binfmt_flat shared libarary > > >support and make maintenance of the code easier. > > > > > >[1] https://lkml.kernel.org/r/81788b56-5b15-7308-38c7-c7f2502c4e15@linux-m68k.org > > >Signed-off-by: "Eric W. Biederman" > > >--- > > > > > >Can the binfmt_flat folks please verify that the shared library support > > >really isn't used? > > > > I don't actually know follow the RISC-V flat support, last I heard it was still > > sort of just in limbo (some toolchain/userspace bugs th at needed to be sorted > > out). Damien would know better, though, he's already on the thread. I'll > > leave it up to him to ack this one, if you were even looking for anything from > > the RISC-V folks at all (we don't have this in any defconfigs). > > For what it's worth, bimfmt_flat (with or without shared library > support) should be simple to implement as a binfmt_misc handler if > anyone needs the old shared library support (or if kernel wanted to > drop it entirely, which I would be in favor of). That's how I handled > old aout binaries I wanted to run after aout was removed: trivial > binfmt_misc loader. Yeah, I was trying to understand why systems were using binfmt_flat and not binfmt_elf, given the mention of elf2flat -- is there really such a large kernel memory footprint savings to be had from removing binfmt_elf? But regardless, yes, it seems like if you're doing anything remotely needing shared libraries with binfmt_flat, such a system could just use ELF instead. -- Kees Cook