linux-kernel - Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

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Message-ID: <20201113225614.ry73o4knb6mvv4dq@treble>
Date:   Fri, 13 Nov 2020 16:56:14 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Jann Horn <jannh@...gle.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

On Fri, Nov 13, 2020 at 02:54:32PM -0800, Sami Tolvanen wrote:
> On Fri, Nov 13, 2020 at 2:34 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >
> > On Fri, Nov 13, 2020 at 12:24:32PM -0800, Sami Tolvanen wrote:
> > > > I still don't see this warning for some reason.
> > >
> > > Do you have CONFIG_XEN enabled? I can reproduce this on ToT master as follows:
> > >
> > > $ git rev-parse HEAD
> > > 585e5b17b92dead8a3aca4e3c9876fbca5f7e0ba
> > > $ make defconfig && \
> > > ./scripts/config -e HYPERVISOR_GUEST -e PARAVIRT -e XEN && \
> > > make olddefconfig && \
> > > make -j110
> > > ...
> > > $ ./tools/objtool/objtool check -arfld vmlinux.o 2>&1 | grep secondary
> > > vmlinux.o: warning: objtool: __startup_secondary_64()+0x2: return with
> > > modified stack frame
> > >
> > > > Is it fixed by adding cpu_bringup_and_idle() to global_noreturns[] in
> > > > tools/objtool/check.c?
> > >
> > > No, that didn't fix the warning. Here's what I tested:
> >
> > I think this fixes it:
> >
> > From: Josh Poimboeuf <jpoimboe@...hat.com>
> > Subject: [PATCH] x86/xen: Fix objtool vmlinux.o validation of xen hypercalls
> >
> > Objtool vmlinux.o validation is showing warnings like the following:
> >
> >   # tools/objtool/objtool check -barfld vmlinux.o
> >   vmlinux.o: warning: objtool: __startup_secondary_64()+0x2: return with modified stack frame
> >   vmlinux.o: warning: objtool:   xen_hypercall_set_trap_table()+0x0: <=== (sym)
> >
> > Objtool falls through all the empty hypercall text and gets confused
> > when it encounters the first real function afterwards.  The empty unwind
> > hints in the hypercalls aren't working for some reason.  Replace them
> > with a more straightforward use of STACK_FRAME_NON_STANDARD.
> >
> > Reported-by: Sami Tolvanen <samitolvanen@...gle.com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > ---
> >  arch/x86/xen/xen-head.S | 9 ++++-----
> >  include/linux/objtool.h | 8 ++++++++
> >  2 files changed, 12 insertions(+), 5 deletions(-)
> 
> Confirmed, this fixes the warning, also in LTO builds. Thanks!
> 
> Tested-by: Sami Tolvanen <samitolvanen@...gle.com>

Good... I'll work through the rest of them.

-- 
Josh