From patchwork Sun Mar 13 15:16:50 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nix X-Patchwork-Id: 11330 Received: (qmail 59395 invoked by alias); 13 Mar 2016 15:19:52 -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 59382 invoked by uid 89); 13 Mar 2016 15:19:51 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=1.4 required=5.0 tests=AWL, BAYES_50, KAM_LAZY_DOMAIN_SECURITY, RP_MATCHES_RCVD autolearn=no version=3.3.2 spammy=sk:stack_p, csu, sk:nickal, sk:STACK_P X-HELO: mail.esperi.org.uk From: Nix To: libc-alpha@sourceware.org Subject: [PATCH 05/17 v6] Open-code the memcpy() at static TLS initialization time. Date: Sun, 13 Mar 2016 15:16:50 +0000 Message-Id: <1457882222-22599-6-git-send-email-nix@esperi.org.uk> In-Reply-To: <1457882222-22599-1-git-send-email-nix@esperi.org.uk> References: <1457882222-22599-1-git-send-email-nix@esperi.org.uk> X-DCC-wuwien-Metrics: spindle 1290; Body=1 Fuz1=1 Fuz2=1 From: Nick Alcock This one is a bit nasty. Now that we are initializing TLS earlier for the stack canary's sake, existing memcpy() implementations become problematic. We can use the multiarch implementations, but they might not always be present, and even if they are present they might not always be in assembler, so might be compiled with stack-protection. We cannot use posix/memcpy.c without marking both it and */wordcopy.c as non-stack- protected, which for memcpy() of all things seems like a seriously bad idea: if any function in glibc should be stack-protected, it's memcpy() (though stack-protecting the many optimized assembly versions is not done in this patch series). So we have two real options: hack up the guts of posix/memcpy.c and */wordcopy.c so that they can be #included (renamed and declared static) inside libc-tls.c, or simply open-code the memcpy(). For simplicity's sake, this patch open-codes it, on the grounds that static binaries are relatively rare and quasi-deprecated anyway, and static binaries with large TLS sections are yet rarer, and not worth the complexity of hacking up all the arch-dependent wordcopy files. If the arch provides an inline assembler memcpy() implementation, we can use that in preference, for speed; also, of course, if stack protection is not enabled at all, we can still use a normal memcpy() as before. (This was not revealed when testing on x86 because on that platform GCC was open-coding the memcpy() for us.) v2: New, lets us remove the memcpy() -fno-stack-protection, which wasn't enough in any case. v4: Add an inhibit_loop_to_libcall to prevent GCC from turning the loop back into a memcpy() again. Wrap long lines. v6: Only do this if stack-protected. Use the inline assembler ARCH_memcpy if available. * csu/libc-tls.c (__libc_setup_tls): Add inhibit_loop_to_libcall to avoid calls to potentially ifunced or stack-protected memcpy. Optionally open-code the TLS-initialization memcpy. --- csu/libc-tls.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/csu/libc-tls.c b/csu/libc-tls.c index 3d67a64..4d81113 100644 --- a/csu/libc-tls.c +++ b/csu/libc-tls.c @@ -102,6 +102,7 @@ init_static_tls (size_t memsz, size_t align) } void +inhibit_loop_to_libcall __libc_setup_tls (size_t tcbsize, size_t tcbalign) { void *tlsblock; @@ -176,8 +177,23 @@ __libc_setup_tls (size_t tcbsize, size_t tcbalign) # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined" #endif _dl_static_dtv[2].pointer.is_static = true; - /* sbrk gives us zero'd memory, so we don't need to clear the remainder. */ + + /* sbrk gives us zero'd memory, so we don't need to clear the remainder. + + When stack-protecting, use inlined asm implementation if available: + otherwise, copy by hand, because memcpy() is stack-protected and is often + multiarch too. */ + +#if defined _HAVE_STRING_ARCH_memcpy || !defined STACK_PROTECTOR_LEVEL memcpy (_dl_static_dtv[2].pointer.val, initimage, filesz); +#else + char *dst = (char *) _dl_static_dtv[2].pointer.val; + char *src = (char *) initimage; + size_t i; + + for (i = 0; i < filesz; dst++, src++, i++) + *dst = *src; +#endif /* Install the pointer to the dtv. */