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 1B134248BB9; Wed, 15 Jan 2025 10:59:23 +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=1736938764; cv=none; b=ulhP1mXtpAC9vLr+X/Y8MLKjQpd32MKVbZXJcgIqMF/M5sJHgsfuROJ0zcKmCyXFR96Yh061XYlPpaLhCpXiBX1r2ipoaIz1GkKE7ikjBouERYSmGsWAYyK9p3hwDq9g0TzQMa2YLEMfSaarZrVTu16Gw8tuymqnA1uxStt9qEE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736938764; c=relaxed/simple; bh=ERelHAiKO37JmEV7mVGENaXzcYRA/BIfBTyt55y7WSQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VB444VzKvK5JOzi9BAtZF6a3ZkB7HHBexfcHeV7WMl4HXtRya4W/7JpB4Tc0QMDubkYslDov1rD63oE2k39Y6HOdY54y1IZp0Ow/C3lOcdzvpx910VlpNNSzRb1Yub/MDVLaDBINMuIJ7XHwYXQVBvKZqhuBuluAnhrYPIiNO9Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=d7thQlmO; 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="d7thQlmO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 32E11C4CEDF; Wed, 15 Jan 2025 10:59:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1736938763; bh=ERelHAiKO37JmEV7mVGENaXzcYRA/BIfBTyt55y7WSQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=d7thQlmO79buGYWpAtxLxN4QvBpS6HeggUTvn7BZHa1/wcxMy+HOn+bZsPpRejKRC W/SuLYyPI/iQfGXNS5Rubcdc6b0cWlIqY11SwpQYObUYOYzOpEGYN8IhimXzVHl1lV HsQpz+fZdu9mhiv9n5+a8pXW5M6a7VxLoZ38liFQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Christina Schimpe , Rick Edgecombe , Dave Hansen Subject: [PATCH 6.6 091/129] x86/fpu: Ensure shadow stack is active before "getting" registers Date: Wed, 15 Jan 2025 11:37:46 +0100 Message-ID: <20250115103557.996269037@linuxfoundation.org> X-Mailer: git-send-email 2.48.0 In-Reply-To: <20250115103554.357917208@linuxfoundation.org> References: <20250115103554.357917208@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: Rick Edgecombe commit a9d9c33132d49329ada647e4514d210d15e31d81 upstream. The x86 shadow stack support has its own set of registers. Those registers are XSAVE-managed, but they are "supervisor state components" which means that userspace can not touch them with XSAVE/XRSTOR. It also means that they are not accessible from the existing ptrace ABI for XSAVE state. Thus, there is a new ptrace get/set interface for it. The regset code that ptrace uses provides an ->active() handler in addition to the get/set ones. For shadow stack this ->active() handler verifies that shadow stack is enabled via the ARCH_SHSTK_SHSTK bit in the thread struct. The ->active() handler is checked from some call sites of the regset get/set handlers, but not the ptrace ones. This was not understood when shadow stack support was put in place. As a result, both the set/get handlers can be called with XFEATURE_CET_USER in its init state, which would cause get_xsave_addr() to return NULL and trigger a WARN_ON(). The ssp_set() handler luckily has an ssp_active() check to avoid surprising the kernel with shadow stack behavior when the kernel is not ready for it (ARCH_SHSTK_SHSTK==0). That check just happened to avoid the warning. But the ->get() side wasn't so lucky. It can be called with shadow stacks disabled, triggering the warning in practice, as reported by Christina Schimpe: WARNING: CPU: 5 PID: 1773 at arch/x86/kernel/fpu/regset.c:198 ssp_get+0x89/0xa0 [...] Call Trace: ? show_regs+0x6e/0x80 ? ssp_get+0x89/0xa0 ? __warn+0x91/0x150 ? ssp_get+0x89/0xa0 ? report_bug+0x19d/0x1b0 ? handle_bug+0x46/0x80 ? exc_invalid_op+0x1d/0x80 ? asm_exc_invalid_op+0x1f/0x30 ? __pfx_ssp_get+0x10/0x10 ? ssp_get+0x89/0xa0 ? ssp_get+0x52/0xa0 __regset_get+0xad/0xf0 copy_regset_to_user+0x52/0xc0 ptrace_regset+0x119/0x140 ptrace_request+0x13c/0x850 ? wait_task_inactive+0x142/0x1d0 ? do_syscall_64+0x6d/0x90 arch_ptrace+0x102/0x300 [...] Ensure that shadow stacks are active in a thread before looking them up in the XSAVE buffer. Since ARCH_SHSTK_SHSTK and user_ssp[SHSTK_EN] are set at the same time, the active check ensures that there will be something to find in the XSAVE buffer. [ dhansen: changelog/subject tweaks ] Fixes: 2fab02b25ae7 ("x86: Add PTRACE interface for shadow stack") Reported-by: Christina Schimpe Signed-off-by: Rick Edgecombe Signed-off-by: Dave Hansen Tested-by: Christina Schimpe Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/20250107233056.235536-1-rick.p.edgecombe%40intel.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/fpu/regset.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c index 6bc1eb2a21bd..887b0b8e21e3 100644 --- a/arch/x86/kernel/fpu/regset.c +++ b/arch/x86/kernel/fpu/regset.c @@ -190,7 +190,8 @@ int ssp_get(struct task_struct *target, const struct user_regset *regset, struct fpu *fpu = &target->thread.fpu; struct cet_user_state *cetregs; - if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK)) + if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK) || + !ssp_active(target, regset)) return -ENODEV; sync_fpstate(fpu); -- 2.48.0