Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 10 Aug 2023 06:40:56 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: Hang when booting guest kernels compiled with clang after SRSO
 mitigations
Message-ID: <20230810134056.GA130730@dev-arch.thelio-3990X>
References: <20230810013334.GA5354@dev-arch.thelio-3990X>
 <20230810081038.GAZNSbftb6DOgg/U7e@fat_crate.local>
 <20230810090835.GBZNSpE6tCw+Ci+9yh@fat_crate.local>
 <20230810101649.GA1795474@dev-arch.thelio-3990X>
 <20230810125122.GIZNTdSuFvA3Cjfexq@fat_crate.local>
 <20230810132706.GA3805855@dev-arch.thelio-3990X>
 <20230810133216.GKZNTm4KpohRR4gVsT@fat_crate.local>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230810133216.GKZNTm4KpohRR4gVsT@fat_crate.local>
Precedence: bulk

On Thu, Aug 10, 2023 at 03:32:16PM +0200, Borislav Petkov wrote:
> On Thu, Aug 10, 2023 at 06:27:06AM -0700, Nathan Chancellor wrote:
> > But my host kernel was compiled using GCC 13.2.0 from kernel.org for the
> > sake of testing to see if the compiler used to build the host kernel had
> > an impact on the problem and it did not.
> 
> Ok, now I'm confused.

Heh, so was I at first when I was doing my regular build and boot tests
of -next :P

> Lemme see if I understand it correctly:
> 
> host kernel:
>  - SRSO enabled
>  - built with gcc
> 
> guest kernel:
>  - built with clang
>  - SRSO not necessary
> 
> Is that the scenario?

Yes, that should be correct.

Host kernel string:

  6.5.0-rc5-00039-g138bcddb86d8 (nathan@dev-arch.thelio-3990X) (x86_64-linux-gcc (GCC) 13.2.0, GNU ld (GNU Binutils) 2.41) #1 SMP PREEMPT_DYNAMIC Wed Aug  9 17:34:43 MST 2023

Guest kernel string:

  6.5.0-rc5 (nathan@dev-arch.thelio-3990X) (ClangBuiltLinux clang version 16.0.6 (https://github.com/llvm/llvm-project 7cbf1a2591520c2491aa35339f227775f4d3adf6), GNU ld (GNU Binutils) 2.41.50.20230809) #1 SMP PREEMPT_DYNAMIC Wed Aug  9 16:54:33 MST 2023

> Anything else?

Shouldn't be. As I noted in the original email, it seems something
specific to the safe-ret mitigation as I don't see the problem with
ibpb, that would be a good canary for making sure that you see the same
behavior.

Cheers,
Nathan