From patchwork Wed Aug 27 15:12:09 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Wielaard X-Patchwork-Id: 2554 Received: (qmail 22438 invoked by alias); 27 Aug 2014 15:12:18 -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 22425 invoked by uid 89); 27 Aug 2014 15:12:17 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.6 required=5.0 tests=AWL, BAYES_00, RP_MATCHES_RCVD, SPF_HELO_PASS, SPF_PASS autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Message-ID: <1409152329.4981.4.camel@bordewijk.wildebeest.org> Subject: Re: [PATCH] i386 TLS_INIT_TP might produce bogus asm changing stack pointer. From: Mark Wielaard To: Roland McGrath Cc: Florian Weimer , libc-alpha@sourceware.org, Siddhesh Poyarekar Date: Wed, 27 Aug 2014 17:12:09 +0200 In-Reply-To: <20140826212902.05AD52C39C1@topped-with-meat.com> References: <1409041665-1558-1-git-send-email-mjw@redhat.com> <53FC469A.2010701@redhat.com> <1409056041.4970.17.camel@bordewijk.wildebeest.org> <20140826212902.05AD52C39C1@topped-with-meat.com> Mime-Version: 1.0 On Tue, 2014-08-26 at 14:29 -0700, Roland McGrath wrote: > The change looks good and even seems probably appropriate to slip in during > the release freeze. That would be great, it does cause some head-scratching for anybody trying to run any i386 program under valgrind with glibc 2.20. > But, per policy, as this has user-visible effects it > needs a bugzilla item filed. Filed https://sourceware.org/bugzilla/show_bug.cgi?id=17319 Updated commit mentioning the bug number in the commit message and ChangeLog entry attached. Thanks, Mark From ab4888b207f07fd762c485f94f9543b0ed456a4d Mon Sep 17 00:00:00 2001 From: Mark Wielaard Date: Wed, 27 Aug 2014 17:07:58 +0200 Subject: [PATCH] i386 TLS_INIT_TP might produce bogus asm changing stack pointer [BZ #17319] TLS_INIT_TP in sysdeps/i386/nptl/tls.h uses some hand written asm to generate a set_thread_area that might result in exchanging ebx and esp around the syscall causing introspection tools like valgrind to loose track of the user stack. Just use INTERNAL_SYSCALL which makes sure esp isn't changed arbitrarily. Before the patch the code would generate: mov $0xf3,%eax movl $0xfffff,0x8(%esp) movl $0x51,0xc(%esp) xchg %esp,%ebx int $0x80 xchg %esp,%ebx Using INTERNAL_SYSCALL instead will generate: movl $0xfffff,0x8(%esp) movl $0x51,0xc(%esp) xchg %ecx,%ebx mov $0xf3,%eax int $0x80 xchg %ecx,%ebx Thanks to Florian Weimer for analysing why the original code generated the bogus esp usage: _segdescr.desc happens to be at the top of the stack, so its address is in %esp. The asm statement says that %3 is an input, so its value will not change, and GCC can use %esp as the input register for the expression &_segdescr.desc. But the constraints do not fully describe the asm statement because the %3 register is actually modified, albeit only temporarily. [BZ #17319] * sysdeps/i386/nptl/tls.h (TLS_INIT_TP): Use INTERNAL_SYSCALL to call set_thread_area instead of hand written asm. (__NR_set_thread_area): Removed define. (TLS_FLAG_WRITABLE): Likewise. (__ASSUME_SET_THREAD_AREA): Remove check. (TLS_EBX_ARG): Remove define. (TLS_LOAD_EBX): Likewise. --- ChangeLog | 11 +++++++++++ sysdeps/i386/nptl/tls.h | 31 ++----------------------------- 2 files changed, 13 insertions(+), 29 deletions(-) diff --git a/ChangeLog b/ChangeLog index 6261ed4..ceeb06b 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,14 @@ +2014-08-27 Mark Wielaard + + [BZ #17319] + * sysdeps/i386/nptl/tls.h (TLS_INIT_TP): Use INTERNAL_SYSCALL + to call set_thread_area instead of hand written asm. + (__NR_set_thread_area): Removed define. + (TLS_FLAG_WRITABLE): Likewise. + (__ASSUME_SET_THREAD_AREA): Remove check. + (TLS_EBX_ARG): Remove define. + (TLS_LOAD_EBX): Likewise. + 2014-08-27 Allan McRae * sysdeps/i386/fpu/libm-test-ulps: Update ULPs. diff --git a/sysdeps/i386/nptl/tls.h b/sysdeps/i386/nptl/tls.h index ac9c9a2..d7302ba 100644 --- a/sysdeps/i386/nptl/tls.h +++ b/sysdeps/i386/nptl/tls.h @@ -154,29 +154,6 @@ union user_desc_init __asm ("movw %w0, %%gs" :: "q" (val)) # endif - -# ifndef __NR_set_thread_area -# define __NR_set_thread_area 243 -# endif -# ifndef TLS_FLAG_WRITABLE -# define TLS_FLAG_WRITABLE 0x00000001 -# endif - -// XXX Enable for the real world. -#if 0 -# ifndef __ASSUME_SET_THREAD_AREA -# error "we need set_thread_area" -# endif -#endif - -# ifdef __PIC__ -# define TLS_EBX_ARG "r" -# define TLS_LOAD_EBX "xchgl %3, %%ebx\n\t" -# else -# define TLS_EBX_ARG "b" -# define TLS_LOAD_EBX -# endif - #if defined NEED_DL_SYSINFO # define INIT_SYSINFO \ _head->sysinfo = GLRO(dl_sysinfo) @@ -231,12 +208,8 @@ tls_fill_user_desc (union user_desc_init *desc, tls_fill_user_desc (&_segdescr, -1, _thrdescr); \ \ /* Install the TLS. */ \ - asm volatile (TLS_LOAD_EBX \ - "int $0x80\n\t" \ - TLS_LOAD_EBX \ - : "=a" (_result), "=m" (_segdescr.desc.entry_number) \ - : "0" (__NR_set_thread_area), \ - TLS_EBX_ARG (&_segdescr.desc), "m" (_segdescr.desc)); \ + INTERNAL_SYSCALL_DECL (err); \ + _result = INTERNAL_SYSCALL (set_thread_area, err, 1, &_segdescr.desc); \ \ if (_result == 0) \ /* We know the index in the GDT, now load the segment register. \ -- 1.9.3