linux-kernel - Re: [PATCH v3 2/6] x86/entry_64: Add VERW just before userspace transition

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Message-ID: <2cda7e85-aa75-4257-864d-0092b3339e0e@suse.com>
Date:   Thu, 26 Oct 2023 19:25:27 +0300
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, tony.luck@...el.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kvm@...r.kernel.org,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        antonio.gomez.iglesias@...ux.intel.com,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v3 2/6] x86/entry_64: Add VERW just before userspace
 transition



On 25.10.23 г. 23:52 ч., Pawan Gupta wrote:

<snip>

> @@ -1520,6 +1530,7 @@ SYM_CODE_START(ignore_sysret)
>   	UNWIND_HINT_END_OF_STACK
>   	ENDBR
>   	mov	$-ENOSYS, %eax
> +	CLEAR_CPU_BUFFERS

nit: Just out of curiosity is it really needed in this case or it's 
doesn for the sake of uniformity so that all ring3 transitions are 
indeed covered??

>   	sysretl
>   SYM_CODE_END(ignore_sysret)
>   #endif
> diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> index 70150298f8bd..245697eb8485 100644
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -271,6 +271,7 @@ SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL)
>   	xorl	%r9d, %r9d
>   	xorl	%r10d, %r10d
>   	swapgs
> +	CLEAR_CPU_BUFFERS
>   	sysretl
>   SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL)
>   	ANNOTATE_NOENDBR
>