linux-kernel - Re: [PATCH v4 00/45] x86: Kernel IBT

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Date:   Wed, 9 Mar 2022 16:30:28 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>, x86@...nel.org,
        joao@...rdrivepizza.com, hjl.tools@...il.com, jpoimboe@...hat.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        keescook@...omium.org, samitolvanen@...gle.com,
        mark.rutland@....com, alyssa.milburn@...el.com, mbenes@...e.cz,
        rostedt@...dmis.org, mhiramat@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, bpf@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v4 00/45] x86: Kernel IBT

On Tue, Mar 8, 2022 at 2:32 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Mar 08, 2022 at 11:01:04PM +0100, Peter Zijlstra wrote:
> > On Tue, Mar 08, 2022 at 12:00:52PM -0800, Alexei Starovoitov wrote:
> > > On Tue, Mar 08, 2022 at 04:30:11PM +0100, Peter Zijlstra wrote:
> > > > Hopefully last posting...
> > > >
> > > > Since last time:
> > > >  - verified clang-14-rc2 works
> > > >   git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git x86/wip.ibt

I observed the following error when building with
CONFIG_LTO_CLANG_FULL=y enabled:

ld.lld: error: ld-temp.o <inline asm>:7:2: symbol 'ibt_selftest_ip' is
already defined
        ibt_selftest_ip:
        ^

Seems to come from
commit a802350ba65a ("x86/ibt: Add IBT feature, MSR and #CP handling")

Commenting out the label in the inline asm, I then observed:
vmlinux.o: warning: objtool: identify_cpu()+0x6d0: sibling call from
callable instruction with modified stack frame
vmlinux.o: warning: objtool: identify_cpu()+0x6e0: stack state
mismatch: cfa1=4+64 cfa2=4+8
These seemed to disappear when I kept CONFIG_LTO_CLANG_FULL=y but then
disabled CONFIG_X86_KERNEL_IBT. (perhaps due to the way I hacked out
the ibt_selftest_ip label).

Otherwise defconfig and CONFIG_LTO_CLANG_THIN=y both built and booted
in a vm WITHOUT IBT support.

Any idea what's the status of IBT emulation in QEMU, and if it exists,
what's the necessary `-cpu` flag to enable it?
-- 
Thanks,
~Nick Desaulniers