linux-hardening - Re: [BUG] missing return thunk: __ret+0x5/0x7e-_

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Date:   Thu, 17 Aug 2023 14:29:03 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Nikolay Borisov <nik.borisov@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        x86@...nel.org, peterz@...radead.org, keescook@...omium.org,
        elver@...gle.com, dvyukov@...gle.com, glider@...gle.com
Subject: Re: [BUG] missing return thunk: __ret+0x5/0x7e-__ret+0x0/0x7e: e9 f6
 ff ff ff

On Thu, Aug 17, 2023 at 11:49:52PM +0300, Nikolay Borisov wrote:
> 
> 
> On 16.08.23 г. 20:54 ч., Paul E. McKenney wrote:
> > Hello!
> > 
> > I hit the splat at the end of this message in recent mainline, and has
> > appeared some time since v6.5-rc1.  Should I be worried?
> > 
> > Reproducer on a two-socket hyperthreaded 20-core-per-socket x86 system:
> > 
> > tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 5m --torture refscale --kcsan --kconfig "CONFIG_NR_CPUS=40" --kmake-args "CC=clang" --bootargs "refscale.scale_type=typesafe_seqlock refscale.nreaders=40 refscale.loops=10000 refscale.holdoff=20 torture.disable_onoff_at_boot refscale.verbose_batched=5 torture.verbose_sleep_frequency=8 torture.verbose_sleep_duration=5"
> > 
> > This is from overnight testing that hit this only in the KCSAN runs.
> > The KASAN and non-debug runs had no trouble.
> > 
> > This commit added the warning long ago:
> > 
> > 65cdf0d623be ("x86/alternative: Report missing return thunk details")
> > 
> > Thoughts?
> > 
> > 							Thanx, Paul
> 
> Likely fixed by the following commit in tip/urgen :
> 4ae68b26c3ab5a82aa271e6e9fc9b1a06e1d6b40 [tip: x86/urgent] objtool/x86: Fix
> SRSO mess

Thank you!  Given the "urgent", I am guessing that this is going
upstream soon?

							Thanx, Paul