From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 831103D47B8; Tue, 21 Apr 2026 14:43:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776782601; cv=none; b=FcTiPRZar4WjCAuTGdzY1U6lPduOk6wF5ZOxVQqAWOpCb3AYyeMG0LxSp6qMRY1sO/Zr9obh7DE76T447uKJaqyXzRaQs0vc5K9QhCWfpgjZC+Upa9csMqPPLKsbeYEdzPXnjBNNMs2324KpYKc7SscHgc98J4z/NKIuw95lr3o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776782601; c=relaxed/simple; bh=MxsGc+EBx86vViVnJi5hkAtx/3njsI58R9adW1EOEhM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=TJLXVlPs+kT0M/QqWVnEzeGF5sB8qzWFvQjGWRTHpINjTvOlfu+Om/vacxSiScrHCHVAkL1aKyWdrDlCBv/8FliV7avcljMgcjRo7ghNB97jbIPN1N811FXSX15qfVTkgyIaahZVGMrW3VT5oyAZfz0OQNTobpfaOvFT26e915U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=FwSQrg72; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="FwSQrg72" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5AC53302C; Tue, 21 Apr 2026 07:43:13 -0700 (PDT) Received: from e123572-lin.arm.com (e123572-lin.cambridge.arm.com [10.1.194.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8AE743FAF5; Tue, 21 Apr 2026 07:43:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1776782598; bh=MxsGc+EBx86vViVnJi5hkAtx/3njsI58R9adW1EOEhM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FwSQrg72snbYiBgDHmR8iZL9vVLCGskUN9cWjinaurZnVDh0UizatL9rkSSH27eV8 yih9/Yypu4gmi6fXvdG3q75fJfAGZf1njQ+YQ/IT7k4I9bVTl8KuQwjpIMiUltfAaQ gOD2ycw3G9mTXWspT0VKRXLH0VvN53JrI17rOPP8= From: Kevin Brodsky To: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, Kevin Brodsky , Catalin Marinas , Joey Gouly , Mark Brown , Shuah Khan , Will Deacon , linux-kselftest@vger.kernel.org Subject: [PATCH 1/4] arm64: signal: Preserve POR_EL0 if poe_context is missing Date: Tue, 21 Apr 2026 15:42:49 +0100 Message-ID: <20260421144252.1440365-2-kevin.brodsky@arm.com> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20260421144252.1440365-1-kevin.brodsky@arm.com> References: <20260421144252.1440365-1-kevin.brodsky@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Commit 2e8a1acea859 ("arm64: signal: Improve POR_EL0 handling to avoid uaccess failures") delayed the write to POR_EL0 in rt_sigreturn to avoid spurious uaccess failures. This change however relies on the poe_context frame record being present: on a system supporting POE, calling sigreturn without a poe_context record now results in writing arbitrary data from the kernel stack into POR_EL0. Fix this by adding a valid_fields member to struct user_access_state, and zeroing the struct on allocation. restore_poe_context() then indicates that the por_el0 field is valid by setting the corresponding bit in valid_fields, and restore_user_access_state() only touches POR_EL0 if there is a valid value to set it to. This is in line with how POR_EL0 was originally handled; all frame records are currently optional, except fpsimd_context. restore_user_access_state() is also called if setting up the signal frame fails, so we also initialise valid_fields in that case. For consistency, setup_sigframe() now also checks valid_fields to decide whether to write a poe_context record, avoiding another call to system_supports_poe(). Fixes: 2e8a1acea859 ("arm64: signal: Improve POR_EL0 handling to avoid uaccess failures") Reported-by: Will Deacon Signed-off-by: Kevin Brodsky --- arch/arm64/kernel/signal.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 08ffc5a5aea4..3f17aed5b4f0 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -67,6 +67,8 @@ struct rt_sigframe_user_layout { unsigned long end_offset; }; +#define UA_STATE_HAS_POR_EL0 BIT(0) + /* * Holds any EL0-controlled state that influences unprivileged memory accesses. * This includes both accesses done in userspace and uaccess done in the kernel. @@ -74,8 +76,12 @@ struct rt_sigframe_user_layout { * This state needs to be carefully managed to ensure that it doesn't cause * uaccess to fail when setting up the signal frame, and the signal handler * itself also expects a well-defined state when entered. + * + * The valid_fields member is a bitfield (see UA_STATE_HAS_*), specifying which + * of the remaining fields is valid (has been set to a value). */ struct user_access_state { + unsigned int valid_fields; u64 por_el0; }; @@ -95,6 +101,7 @@ static void save_reset_user_access_state(struct user_access_state *ua_state) por_enable_all |= POR_ELx_PERM_PREP(pkey, POE_RWX); ua_state->por_el0 = read_sysreg_s(SYS_POR_EL0); + ua_state->valid_fields |= UA_STATE_HAS_POR_EL0; write_sysreg_s(por_enable_all, SYS_POR_EL0); /* * No ISB required as we can tolerate spurious Overlay faults - @@ -122,7 +129,7 @@ static void set_handler_user_access_state(void) */ static void restore_user_access_state(const struct user_access_state *ua_state) { - if (system_supports_poe()) + if (ua_state->valid_fields & UA_STATE_HAS_POR_EL0) write_sysreg_s(ua_state->por_el0, SYS_POR_EL0); } @@ -352,8 +359,10 @@ static int restore_poe_context(struct user_ctxs *user, return -EINVAL; __get_user_error(por_el0, &(user->poe->por_el0), err); - if (!err) + if (!err) { ua_state->por_el0 = por_el0; + ua_state->valid_fields |= UA_STATE_HAS_POR_EL0; + } return err; } @@ -1095,7 +1104,7 @@ SYSCALL_DEFINE0(rt_sigreturn) { struct pt_regs *regs = current_pt_regs(); struct rt_sigframe __user *frame; - struct user_access_state ua_state; + struct user_access_state ua_state = {0}; /* Always make any pending restarted system calls return -EINTR */ current->restart_block.fn = do_no_restart_syscall; @@ -1302,7 +1311,7 @@ static int setup_sigframe(struct rt_sigframe_user_layout *user, err |= preserve_fpmr_context(fpmr_ctx); } - if (system_supports_poe() && err == 0) { + if ((ua_state->valid_fields & UA_STATE_HAS_POR_EL0) && err == 0) { struct poe_context __user *poe_ctx = apply_user_offset(user, user->poe_offset); @@ -1507,7 +1516,7 @@ static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set, { struct rt_sigframe_user_layout user; struct rt_sigframe __user *frame; - struct user_access_state ua_state; + struct user_access_state ua_state = {0}; int err = 0; fpsimd_save_and_flush_current_state(); -- 2.51.2