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From: Peter Zijlstra <peterz@infradead.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Arnd Bergmann <arnd@arndb.de>, Jann Horn <jannh@google.com>,
	Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH 07/22] x86/uaccess: Remove ELF function annotation from copy_user_handle_tail()
Date: Tue, 16 Jul 2019 20:51:44 +0200	[thread overview]
Message-ID: <20190716185144.GI3402@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKwvOdn2ZEe6y=TZ2OyphR7CrC3yJgDEUVtwSX_5fXGtYAQ=bA@mail.gmail.com>

On Tue, Jul 16, 2019 at 11:16:48AM -0700, Nick Desaulniers wrote:
> On Sun, Jul 14, 2019 at 5:37 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >
> > After an objtool improvement, it's complaining about the CLAC in
> > copy_user_handle_tail():
> >
> >   arch/x86/lib/copy_user_64.o: warning: objtool: .altinstr_replacement+0x12: redundant UACCESS disable
> >   arch/x86/lib/copy_user_64.o: warning: objtool:   copy_user_handle_tail()+0x6: (alt)
> >   arch/x86/lib/copy_user_64.o: warning: objtool:   copy_user_handle_tail()+0x2: (alt)
> >   arch/x86/lib/copy_user_64.o: warning: objtool:   copy_user_handle_tail()+0x0: <=== (func)
> >
> > copy_user_handle_tail() is incorrectly marked as a callable function, so
> > objtool is rightfully concerned about the CLAC with no corresponding
> > STAC.
> >
> > Remove the ELF function annotation.  The copy_user_handle_tail() code
> > path is already verified by objtool because it's jumped to by other
> > callable asm code (which does the corresponding STAC).
> 
> What is CLAC and STAC?

CLear AC flag and SeT AC flag, SMAP repurposed the EFLAGS.AC for CPL0.

Also see commit: ea24213d8088 ("objtool: Add UACCESS validation")

  reply	other threads:[~2019-07-16 18:51 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-15  0:36 [PATCH 00/22] x86, objtool: several fixes/improvements Josh Poimboeuf
2019-07-15  0:36 ` [PATCH 01/22] x86/paravirt: Fix callee-saved function ELF sizes Josh Poimboeuf
2019-07-15  4:58   ` Juergen Gross
2019-07-15 12:43     ` Josh Poimboeuf
2019-07-15  0:36 ` [PATCH 02/22] x86/kvm: Fix fastop function ELF metadata Josh Poimboeuf
2019-07-15  9:05   ` Paolo Bonzini
2019-07-15  0:36 ` [PATCH 03/22] x86/kvm: Fix frame pointer usage in vmx_vmenter() Josh Poimboeuf
2019-07-15  9:04   ` Paolo Bonzini
2019-07-15 12:37     ` Josh Poimboeuf
2019-07-15 13:03       ` Paolo Bonzini
2019-07-15 13:35         ` Josh Poimboeuf
2019-07-15 18:17           ` Paolo Bonzini
2019-07-15  0:36 ` [PATCH 04/22] x86/kvm: Don't call kvm_spurious_fault() from .fixup Josh Poimboeuf
2019-07-15  9:07   ` Paolo Bonzini
2019-07-15 12:40     ` Josh Poimboeuf
2019-07-15 13:05       ` Paolo Bonzini
2019-07-15 13:25         ` Josh Poimboeuf
2019-07-15 18:16           ` Paolo Bonzini
2019-07-15  0:37 ` [PATCH 05/22] x86/entry: Fix thunk function ELF sizes Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 06/22] x86/head/64: Annotate start_cpu0() as non-callable Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 07/22] x86/uaccess: Remove ELF function annotation from copy_user_handle_tail() Josh Poimboeuf
2019-07-16 18:16   ` Nick Desaulniers
2019-07-16 18:51     ` Peter Zijlstra [this message]
2019-07-15  0:37 ` [PATCH 08/22] x86/uaccess: Don't leak AC flag into fentry from mcsafe_handle_tail() Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 09/22] x86/uaccess: Remove redundant CLACs in getuser/putuser error paths Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 10/22] bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() Josh Poimboeuf
2019-07-16 18:15   ` Nick Desaulniers
2019-07-16 23:02     ` Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 11/22] objtool: Add mcsafe_handle_tail() to the uaccess safe list Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 12/22] objtool: Track original function across branches Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 13/22] objtool: Refactor function alias logic Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 14/22] objtool: Warn on zero-length functions Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 15/22] objtool: Change dead_end_function() to return boolean Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 16/22] objtool: Do frame pointer check before dead end check Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 17/22] objtool: Refactor sibling call detection logic Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 18/22] objtool: Refactor jump table code Josh Poimboeuf
2019-07-15  9:38   ` Peter Zijlstra
2019-07-15  0:37 ` [PATCH 19/22] objtool: Support repeated uses of the same C jump table Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 20/22] objtool: Fix seg fault on bad switch table entry Josh Poimboeuf
2019-07-15 17:24   ` Nick Desaulniers
2019-07-15 17:29     ` Josh Poimboeuf
2019-07-18 23:02       ` Nick Desaulniers
2019-07-15  0:37 ` [PATCH 21/22] objtool: convert insn type to enum Josh Poimboeuf
2019-07-15  0:37 ` [PATCH 22/22] objtool: Support conditional retpolines Josh Poimboeuf
2019-07-15  9:52 ` [PATCH 00/22] x86, objtool: several fixes/improvements Peter Zijlstra
2019-07-15 19:38 ` Josh Poimboeuf
2019-07-15 21:45   ` Nick Desaulniers
2019-07-16 23:17     ` Josh Poimboeuf
2019-07-18 22:26       ` Nick Desaulniers
2019-09-27 20:24         ` Nick Desaulniers

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