From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754912AbbCMWi7 (ORCPT ); Fri, 13 Mar 2015 18:38:59 -0400 Received: from mail-lb0-f169.google.com ([209.85.217.169]:45983 "EHLO mail-lb0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752082AbbCMWiy (ORCPT ); Fri, 13 Mar 2015 18:38:54 -0400 MIME-Version: 1.0 In-Reply-To: <20150313223139.GD10954@cloud> References: <20150313223139.GD10954@cloud> From: Andy Lutomirski Date: Fri, 13 Mar 2015 15:38:31 -0700 Message-ID: Subject: Re: [PATCH 2/6] x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit To: Josh Triplett Cc: Al Viro , Andrew Morton , Ingo Molnar , Kees Cook , Oleg Nesterov , "Paul E. McKenney" , "H. Peter Anvin" , Rik van Riel , Thomas Gleixner , Thiago Macieira , Michael Kerrisk , "linux-kernel@vger.kernel.org" , Linux API , Linux FS Devel , X86 ML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 13, 2015 at 3:31 PM, wrote: > On Fri, Mar 13, 2015 at 03:01:16PM -0700, Andy Lutomirski wrote: >> On Thu, Mar 12, 2015 at 6:40 PM, Josh Triplett wrote: >> > For 32-bit userspace on a 64-bit kernel, this requires modifying >> > stub32_clone to actually swap the appropriate arguments to match >> > CONFIG_CLONE_BACKWARDS, rather than just leaving the C argument for tls >> > broken. >> > >> > Signed-off-by: Josh Triplett >> > Signed-off-by: Thiago Macieira >> > --- >> > arch/x86/Kconfig | 1 + >> > arch/x86/ia32/ia32entry.S | 2 +- >> > arch/x86/kernel/process_32.c | 6 +++--- >> > arch/x86/kernel/process_64.c | 8 ++++---- >> > 4 files changed, 9 insertions(+), 8 deletions(-) >> > >> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >> > index b7d31ca..4960b0d 100644 >> > --- a/arch/x86/Kconfig >> > +++ b/arch/x86/Kconfig >> > @@ -124,6 +124,7 @@ config X86 >> > select MODULES_USE_ELF_REL if X86_32 >> > select MODULES_USE_ELF_RELA if X86_64 >> > select CLONE_BACKWARDS if X86_32 >> > + select HAVE_COPY_THREAD_TLS >> > select ARCH_USE_BUILTIN_BSWAP >> > select ARCH_USE_QUEUE_RWLOCK >> > select OLD_SIGSUSPEND3 if X86_32 || IA32_EMULATION >> > diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S >> > index 156ebca..0286735 100644 >> > --- a/arch/x86/ia32/ia32entry.S >> > +++ b/arch/x86/ia32/ia32entry.S >> > @@ -487,7 +487,7 @@ GLOBAL(\label) >> > ALIGN >> > GLOBAL(stub32_clone) >> > leaq sys_clone(%rip),%rax >> > - mov %r8, %rcx >> > + xchg %r8, %rcx >> > jmp ia32_ptregs_common >> >> Do I understand correct that whatever function this is a stub for just >> takes its arguments in the wrong order? If so, can we just fix it >> instead of using xchg here? > > 32-bit x86 and 64-bit x86 take the arguments to clone in a different > order, and stub32_clone fixes up the argument order then calls the > 64-bit sys_clone. > > I'd love to see *all* the 32-on-64 compat stubs for clone rewritten in C > under CONFIG_COMPAT. However, doing so would require encoding the > knowledge for each 64-bit architecture for how its corresponding 32-bit > architecture accepts arguments to clone, which is information that the > current CONFIG_CLONE_BACKWARDS{1,2,3} don't include; it would then > require cleaning up all the architecture-specific assembly stubs for > 32-bit clone entry points. > > In the meantime, doing that *just* for 32-bit x86 on 64-bit x86 doesn't > seem worth it, since it would require adding a new C entry point for > compat_sys_clone under arch/x86 somewhere. > > One cleanup at a time. :) Fine w/ me. > >> In general, I much prefer C code to new asm where it makes sense to >> make this tradeoff. > > Agreed completely. However, this is at least conservation-of-asm, or > reduction if you consider the pt_regs argument-grabbing hack to be > asm-esque code. > >> Other than that, this is a huge improvement. You'll have minor >> conflicts against -tip, though. > > Right, I've seen your current changes there. Should be a trivial merge > though. > > Would you mind providing an ack for the series, or at least for the > first two patches? I can give you an ok-in-principle on the first two. I'd need to stare at the awful code for a bit to understand the @!*&! clone variants to really ack them convincingly. OTOH, it would be rather surprising if you messed it up in a way that still boots on all three variants (native 32-bit, native 64-bit, and compat). So, for the first two patches: Acked-by: Andy Lutomirski # assuming all bitnesses boot --Andy > > (I'm wondering whose tree this series ought to go through, for that > matter.) > > - Josh Triplett -- Andy Lutomirski AMA Capital Management, LLC