From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 75AFB1D86F1; Mon, 6 Jan 2025 15:27:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736177241; cv=none; b=lXNkGpJqfiItIsXxBYLTzP6Y7fJjGyOLsgBImmCsGo5kqS4j0t1dLhnuR3I0CVwOmTDSmDfqdlceCEpLCNy/49tJMxyuQMZ6pCKbnp1GCwc1omL0D1SDvzJRAMl5hRCaQfahpsuCk5zgy8/jt29oPDOf+WS3e+XlgweFUbeInCc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736177241; c=relaxed/simple; bh=bROvTR9ejw47CNelZQ5LOgaoxK4BrFOQ9zUqcD30t9Q=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cF5sQ4+t/2aLuFqo6Db4uBwG0Vxk5YJek/aeqJyjnZ5UNW2R8S9iHQu3ACr01gbTf7dHVg+E2+3jN0etjpMOvvbb+dImKJK4i5Bo2/9+OcKd1ABJrwWwayktxybcmMA12qnlAZ9Dlw2Nr306Vmsd+DVOt2wBXTM8ueUO9fxhKUA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=J4z4xywp; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="J4z4xywp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DAFB0C4CEDF; Mon, 6 Jan 2025 15:27:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1736177241; bh=bROvTR9ejw47CNelZQ5LOgaoxK4BrFOQ9zUqcD30t9Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J4z4xywplK0ryya/+4yFxcJEImH14tFvk4NP7up44bq7PHPS3ID0FH7Tcm5GlKRre Wo6VKBlObgSmeWudMSR/8ftUXrx4wnZdej5y7h9qLhvjdIbFjjGBHNNgbHznyo0Uxm /vU/GzSUnWGZaCUfAeWb/pkAaLeVgsdO/4j/jF0M= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Xin Li (Intel)" , Dave Hansen , Ingo Molnar , Sasha Levin Subject: [PATCH 6.6 099/222] x86/fred: Clear WFE in missing-ENDBRANCH #CPs Date: Mon, 6 Jan 2025 16:15:03 +0100 Message-ID: <20250106151154.343171694@linuxfoundation.org> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250106151150.585603565@linuxfoundation.org> References: <20250106151150.585603565@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Xin Li (Intel) [ Upstream commit dc81e556f2a017d681251ace21bf06c126d5a192 ] An indirect branch instruction sets the CPU indirect branch tracker (IBT) into WAIT_FOR_ENDBRANCH (WFE) state and WFE stays asserted across the instruction boundary. When the decoder finds an inappropriate instruction while WFE is set ENDBR, the CPU raises a #CP fault. For the "kernel IBT no ENDBR" selftest where #CPs are deliberately triggered, the WFE state of the interrupted context needs to be cleared to let execution continue. Otherwise when the CPU resumes from the instruction that just caused the previous #CP, another missing-ENDBRANCH #CP is raised and the CPU enters a dead loop. This is not a problem with IDT because it doesn't preserve WFE and IRET doesn't set WFE. But FRED provides space on the entry stack (in an expanded CS area) to save and restore the WFE state, thus the WFE state is no longer clobbered, so software must clear it. Clear WFE to avoid dead looping in ibt_clear_fred_wfe() and the !ibt_fatal code path when execution is allowed to continue. Clobbering WFE in any other circumstance is a security-relevant bug. [ dhansen: changelog rewording ] Fixes: a5f6c2ace997 ("x86/shstk: Add user control-protection fault handler") Signed-off-by: Xin Li (Intel) Signed-off-by: Dave Hansen Signed-off-by: Ingo Molnar Acked-by: Dave Hansen Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20241113175934.3897541-1-xin%40zytor.com Signed-off-by: Sasha Levin --- arch/x86/kernel/cet.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c index d2c732a34e5d..303bf74d175b 100644 --- a/arch/x86/kernel/cet.c +++ b/arch/x86/kernel/cet.c @@ -81,6 +81,34 @@ static void do_user_cp_fault(struct pt_regs *regs, unsigned long error_code) static __ro_after_init bool ibt_fatal = true; +/* + * By definition, all missing-ENDBRANCH #CPs are a result of WFE && !ENDBR. + * + * For the kernel IBT no ENDBR selftest where #CPs are deliberately triggered, + * the WFE state of the interrupted context needs to be cleared to let execution + * continue. Otherwise when the CPU resumes from the instruction that just + * caused the previous #CP, another missing-ENDBRANCH #CP is raised and the CPU + * enters a dead loop. + * + * This is not a problem with IDT because it doesn't preserve WFE and IRET doesn't + * set WFE. But FRED provides space on the entry stack (in an expanded CS area) + * to save and restore the WFE state, thus the WFE state is no longer clobbered, + * so software must clear it. + */ +static void ibt_clear_fred_wfe(struct pt_regs *regs) +{ + /* + * No need to do any FRED checks. + * + * For IDT event delivery, the high-order 48 bits of CS are pushed + * as 0s into the stack, and later IRET ignores these bits. + * + * For FRED, a test to check if fred_cs.wfe is set would be dropped + * by compilers. + */ + regs->fred_cs.wfe = 0; +} + static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code) { if ((error_code & CP_EC) != CP_ENDBR) { @@ -90,6 +118,7 @@ static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code) if (unlikely(regs->ip == (unsigned long)&ibt_selftest_noendbr)) { regs->ax = 0; + ibt_clear_fred_wfe(regs); return; } @@ -97,6 +126,7 @@ static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code) if (!ibt_fatal) { printk(KERN_DEFAULT CUT_HERE); __warn(__FILE__, __LINE__, (void *)regs->ip, TAINT_WARN, regs, NULL); + ibt_clear_fred_wfe(regs); return; } BUG(); -- 2.39.5