From nobody Wed Dec 17 08:44:14 2025 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 50D6423372A for ; Mon, 24 Feb 2025 12:46:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740401163; cv=none; b=JdDxTD/ymycn8eqr80joiAvWtgbl62DwZnZ7c03sUfxNQOrRL36t04AF60PI41louZm5i8AFzOlYON4tZt4W83XPtOfVT4JfW9dM0mAYycaJIEyExvKQ48Avapv6PCJVZ2EItMxj8IvlQShyNPYc7/GBfq+hl0BJR3DsL9zqkec= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740401163; c=relaxed/simple; bh=qiHWEsUFhyrAhvzR/3W2KqNPPoF05MG34ACD4hT96GM=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=UJ6ffqP55UoZRBNSRXfdXqOe+sksGQ4UJ/1FFhIvFaGrVR2NGTWvb/YVjPiPKet8leg1+8uHXBkf2eC2vUevXNtK7rQ8mYWRQ7DKDG4SGbJULVn+SnV4bHF5bG6OcxVt4a768ZHOAVodyqpsdAdweJt0/Qn66Rx2GdOt9Ebof+k= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=P9azl+wq; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="P9azl+wq" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=XBH0IHGZUCGG4OKLWJTsoSfxC5AGMSYb5ZmdUnOdGdE=; b=P9azl+wqq1NuEIBo/OoXMGmsgD SED9BZrXD6cuLTFlqCokO/1VK82YPNcf9wyV+fTFzm/ZC8LIgYSSIPPxC6rCYSLrYUtsF4pP0mE25 eWM5vRAEGoCIBzNXnQxli8bHDBadAUf9L/MSc+Rj+1JHRnZXW0MUZFOvvuNZxfsln0AltCgk6v5jC AnKr7Nl6Y39TdU1YO1i9/vJeNRpD2XknSZDWlkwNFMiaE6fR//JUMF6sA7SadHmj/IrHUfptsUjB2 glnGf7FPruIUY4L3mffOg07l/eZfbho2ydorJhjsF14ORM/4RuTr3oU531emFueo75JqOBf8ZXvXo 38R9zcKg==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tmXqM-000000079lb-2IxM; Mon, 24 Feb 2025 12:45:54 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id 18E6C3007F0; Mon, 24 Feb 2025 13:45:54 +0100 (CET) Message-ID: <20250224124200.059556588@infradead.org> User-Agent: quilt/0.66 Date: Mon, 24 Feb 2025 13:37:05 +0100 From: Peter Zijlstra To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, alyssa.milburn@intel.com, scott.d.constable@intel.com, joao@overdrivepizza.com, andrew.cooper3@citrix.com, jpoimboe@kernel.org, jose.marchesi@oracle.com, hjl.tools@gmail.com, ndesaulniers@google.com, samitolvanen@google.com, nathan@kernel.org, ojeda@kernel.org, kees@kernel.org, alexei.starovoitov@gmail.com, mhiramat@kernel.org, jmill@asu.edu Subject: [PATCH v4 02/10] x86/ibt: Add exact_endbr() helper References: <20250224123703.843199044@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For when we want to exactly match ENDBR, and not everything that we can scribble it with. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Kees Cook --- arch/x86/kernel/alternative.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -863,6 +863,17 @@ __noendbr bool is_endbr(u32 *val) return false; } =20 +static __noendbr bool exact_endbr(u32 *val) +{ + u32 endbr; + + __get_kernel_nofault(&endbr, val, u32, Efault); + return endbr =3D=3D gen_endbr(); + +Efault: + return false; +} + static void poison_cfi(void *addr); =20 static void __init_or_module poison_endbr(void *addr) @@ -1427,10 +1438,9 @@ static void poison_cfi(void *addr) bool decode_fineibt_insn(struct pt_regs *regs, unsigned long *target, u32 = *type) { unsigned long addr =3D regs->ip - fineibt_preamble_ud2; - u32 endbr, hash; + u32 hash; =20 - __get_kernel_nofault(&endbr, addr, u32, Efault); - if (endbr !=3D gen_endbr()) + if (!exact_endbr((void *)addr)) return false; =20 *target =3D addr + fineibt_preamble_size;