From patchwork Mon Dec 19 11:15:19 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nix X-Patchwork-Id: 18560 Received: (qmail 101065 invoked by alias); 19 Dec 2016 11:15:49 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 100826 invoked by uid 89); 19 Dec 2016 11:15:47 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL, BAYES_40, KAM_LAZY_DOMAIN_SECURITY, RP_MATCHES_RCVD autolearn=ham version=3.3.2 spammy=dragged, objpfx, rm, common-objpfx X-HELO: mail.esperi.org.uk From: Nix To: libc-alpha@sourceware.org Cc: fweimer@redhat.com Subject: [PATCH 06/15] Prevent the rtld mapfile computation from dragging in __stack_chk_fail*. Date: Mon, 19 Dec 2016 11:15:19 +0000 Message-Id: <20161219111528.14969-7-nix@esperi.org.uk> In-Reply-To: <20161219111528.14969-1-nix@esperi.org.uk> References: <20161219111528.14969-1-nix@esperi.org.uk> X-DCC--Metrics: spindle 1480; Body=2 Fuz1=2 Fuz2=2 From: Nick Alcock The previous commit prevented rtld itself from being built with -fstack-protector, but this is not quite enough. We identify which objects belong in rtld via a test link and analysis of the resulting mapfile. That link is necessarily done against objects that are stack-protected, so drags in __stack_chk_fail_local, __stack_chk_fail, and all the libc and libio code they use. To stop this happening, use --defsym in the test librtld.map-production link to force the linker to predefine these two symbols (to 0, but it could be to anything). (In a real link, this would of course be catastrophic, but these object files are never used for anything else.) v2: New. v6: Dummy out stack_chk_fail_local too. v7: Fix word-wrapping. * elf/Makefile (dummy-stack-chk-fail): New. ($(objpfx)librtld.map): Use it. --- elf/Makefile | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/elf/Makefile b/elf/Makefile index d14d48d..daf0ebd 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -369,9 +369,22 @@ $(objpfx)dl-allobjs.os: $(all-rtld-routines:%=$(objpfx)%.os) # are compiled with special flags, and puts these modules into rtld-libc.a # for us. Then we do the real link using rtld-libc.a instead of libc_pic.a. +# If the compiler can do SSP, build the mapfile with dummy __stack_chk_fail +# and __stack_chk_fail_local symbols defined, to prevent the real things +# being dragged into rtld even though rtld is never built with stack- +# protection. + +ifeq ($(have-ssp),yes) +dummy-stack-chk-fail := -Wl,--defsym='__stack_chk_fail=0' \ + -Wl,--defsym='__stack_chk_fail_local=0' +else +dummy-stack-chk-fail := +endif + $(objpfx)librtld.map: $(objpfx)dl-allobjs.os $(common-objpfx)libc_pic.a @-rm -f $@T - $(reloc-link) -o $@.o '-Wl,-(' $^ -lgcc '-Wl,-)' -Wl,-Map,$@T + $(reloc-link) -o $@.o $(dummy-stack-chk-fail) \ + '-Wl,-(' $^ -lgcc '-Wl,-)' -Wl,-Map,$@T rm -f $@.o mv -f $@T $@