linux-kernel - Re: [RFC PATCH 40/56] x86/alternative: Use sync_core_nmi

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251016103549.GD3289052@noisy.programming.kicks-ass.net>
Date: Thu, 16 Oct 2025 12:35:49 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: David Kaplan <david.kaplan@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>, Alexander Graf <graf@...zon.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 40/56] x86/alternative: Use sync_core_nmi_safe()

On Mon, Oct 13, 2025 at 09:34:28AM -0500, David Kaplan wrote:
> Re-patching is done under NMI context so the NMI-safe version of
> sync_core() must be used.
> 
> Signed-off-by: David Kaplan <david.kaplan@....com>
> ---
>  arch/x86/kernel/alternative.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index b67116ae883c..2d48d750d4d9 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -2585,7 +2585,11 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
>  	} else {
>  		local_irq_save(flags);
>  		memcpy(addr, opcode, len);
> -		sync_core();
> +		/* Re-patching occurs in NMI context so we can't do IRET. */
> +		if (repatch_in_progress)
> +			sync_core_nmi_safe();
> +		else
> +			sync_core();
>  		local_irq_restore(flags);
>  

Can we please keep this in sync_core()? Something like:

static __always_inline void sync_core(void)
{
	if (static_cpu_has(X86_FEATURE_SERIALIZE)) {
		serialize();
		return;
	}

+	if (repatch_in_progress) {
+		sync_core_nmi_safe();
+		return;
+	}
+
	iret_to_self();
}

That way all the modern stuff that has SERIALIZE will still use that.