From: josh@joshtriplett.org
To: Andy Lutomirski <luto@amacapital.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@redhat.com>, Kees Cook <keescook@chromium.org>,
Oleg Nesterov <oleg@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
"H. Peter Anvin" <hpa@zytor.com>, Rik van Riel <riel@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Thiago Macieira <thiago.macieira@intel.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
X86 ML <x86@kernel.org>
Subject: Re: [PATCH 2/6] x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit
Date: Fri, 13 Mar 2015 16:01:53 -0700 [thread overview]
Message-ID: <20150313230153.GA11441@cloud> (raw)
In-Reply-To: <CALCETrW3kJSVz4ffVC6YdB+ELukhOHNgPFKZSziMq5nn_Nq3Zg@mail.gmail.com>
On Fri, Mar 13, 2015 at 03:45:16PM -0700, Andy Lutomirski wrote:
> On Fri, Mar 13, 2015 at 3:43 PM, <josh@joshtriplett.org> wrote:
> > On Fri, Mar 13, 2015 at 03:38:31PM -0700, Andy Lutomirski wrote:
> >> On Fri, Mar 13, 2015 at 3:31 PM, <josh@joshtriplett.org> 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 <josh@joshtriplett.org> 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 <josh@joshtriplett.org>
> >> >> > Signed-off-by: Thiago Macieira <thiago.macieira@intel.com>
> >> >> > ---
> >> >> > 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.
> >
> > Thanks.
> >
> >> >
> >> >> 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.
> >
> > I'd definitely appreciate the staring. :)
> >
> >> 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 <luto@kernel.org> # assuming all bitnesses boot
> >
> > I did test all three, not just with booting but with a thread-local
> > storage test.
>
> And it's fairly clear that no one ever tested clone-based TLS in 32
> bits from a 64-bit ELF binary, because it was broken until very
> recently :-/
I'm not sure *anyone* other than exploit-seekers test 32-bit system
calls from a 64-bit binary. :)
> This stuff is too magical and too poorly documented for my tastes.
Agreed. That was my reaction when I figured out what was happening with
CLONE_SETTLS and pt_regs, and my goal with the first two patches in this
series was precisely to make it *less* magical. :)
- Josh Triplett
next prev parent reply other threads:[~2015-03-13 23:02 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-13 1:40 [PATCH 0/6] CLONE_FD: Task exit notification via file descriptor Josh Triplett
2015-03-13 1:40 ` [PATCH 1/6] clone: Support passing tls argument via C rather than pt_regs magic Josh Triplett
2015-03-13 1:40 ` [PATCH 2/6] x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit Josh Triplett
2015-03-13 22:01 ` Andy Lutomirski
2015-03-13 22:31 ` josh
2015-03-13 22:38 ` Andy Lutomirski
2015-03-13 22:43 ` josh
2015-03-13 22:45 ` Andy Lutomirski
2015-03-13 23:01 ` josh [this message]
2015-03-13 1:40 ` [PATCH 3/6] Introduce a new clone4 syscall with more flag bits and extensible arguments Josh Triplett
2015-03-13 1:40 ` [PATCH 4/6] signal: Factor out a helper function to process task_struct exit_code Josh Triplett
2015-03-13 1:40 ` [PATCH 5/6] fs: Make alloc_fd non-private Josh Triplett
2015-03-13 1:41 ` [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd Josh Triplett
2015-03-13 16:21 ` Oleg Nesterov
2015-03-13 19:57 ` josh
2015-03-13 21:34 ` Andy Lutomirski
2015-03-13 22:20 ` josh
2015-03-13 22:28 ` Andy Lutomirski
2015-03-13 22:34 ` josh
2015-03-13 22:38 ` Andy Lutomirski
2015-03-14 14:14 ` Oleg Nesterov
2015-03-14 14:32 ` Oleg Nesterov
2015-03-14 18:38 ` Thiago Macieira
2015-03-14 18:54 ` Oleg Nesterov
2015-03-14 22:03 ` Josh Triplett
2015-03-14 22:26 ` Thiago Macieira
2015-03-14 19:01 ` Josh Triplett
2015-03-14 19:18 ` Oleg Nesterov
2015-03-14 19:47 ` Oleg Nesterov
2015-03-14 20:14 ` Josh Triplett
2015-03-14 20:30 ` Oleg Nesterov
2015-03-14 22:14 ` Josh Triplett
2015-03-14 20:03 ` Josh Triplett
2015-03-14 20:20 ` Oleg Nesterov
2015-03-14 22:09 ` Josh Triplett
2015-03-14 14:35 ` Oleg Nesterov
2015-03-14 19:15 ` Josh Triplett
2015-03-14 19:24 ` Oleg Nesterov
2015-03-14 19:48 ` Josh Triplett
2015-03-13 1:41 ` [PATCH] clone4.2: New manpage documenting clone4(2) Josh Triplett
2015-03-13 2:07 ` [PATCH 0/6] CLONE_FD: Task exit notification via file descriptor Thiago Macieira
2015-03-13 16:05 ` David Drysdale
2015-03-13 19:42 ` Josh Triplett
2015-03-13 21:16 ` Thiago Macieira
2015-03-13 21:44 ` josh
2015-03-13 21:33 ` Andy Lutomirski
2015-03-13 21:45 ` josh
2015-03-13 21:51 ` Andy Lutomirski
2015-03-14 1:11 ` Thiago Macieira
2015-03-14 19:03 ` Thiago Macieira
2015-03-14 19:29 ` Josh Triplett
2015-03-15 10:18 ` David Drysdale
2015-03-15 10:59 ` Josh Triplett
2015-03-15 8:55 ` David Drysdale
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