linux-kernel - Re: [PATCH 07/22] x86/uaccess: Remove ELF function annotation from copy_user_handle

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190716185144.GI3402@hirez.programming.kicks-ass.net>
Date:   Tue, 16 Jul 2019 20:51:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH 07/22] x86/uaccess: Remove ELF function annotation from
 copy_user_handle_tail()

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@...hat.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")