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 5674937B413; Mon, 27 Apr 2026 12:04:02 +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=1777291444; cv=none; b=jRlQmPkefJNVUHUjBaAduQH7cTm2B09z3bl9Cp4nb4NMyvPiBm1Xp/1PFCt0dmIIrSJbl2/EFBvH5L6QN/STx70iREH6e7d/H73FhH0Du8Aac7MzjnNgKAJQqHpB5otHdaQVRb3TWSsFyixbyq/cXPA2dj6ligekqfttX1Ww+hU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777291444; c=relaxed/simple; bh=slrafw9MOFyBo/v8zwX3peiajbdJyOH74VvtDwDB9UQ=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=CFks1C1jLzN7a1belVCjOdcI+qivI81GYywjkLwzvgL1cMeuVZNDH9OZeUg9u6idDveOnkEMeSV98S40CRrZFoAYalA9XFFEP4EKPRYRNYtAbPl5uy8GVX7C5OXJ3EJeBQfWLx1l2OgN0fnsKnIzKL8srEbvXTNLQ8nqMSlELko= 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=vxg2AMkE; 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="vxg2AMkE" 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 360C91FC7; Mon, 27 Apr 2026 05:03:56 -0700 (PDT) Received: from localhost.localdomain (e123572-lin.cambridge.arm.com [10.1.194.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 177223F62B; Mon, 27 Apr 2026 05:03:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1777291441; bh=slrafw9MOFyBo/v8zwX3peiajbdJyOH74VvtDwDB9UQ=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=vxg2AMkEnOQuZ6mDO6cV3q3P+xPWKKgasAMEAyIb23+H/+HglfDlScLV73Cp5qVaD Nyg1f0E/85GwcF2+uUWgldgKYrq9DOcI1gg40nhD3hcgHWReH/d20w7e8SiUQyk/k3 Fuyna3CGcPTJzFlnulf41IrAk0CI+0/cZriDXirA= From: Kevin Brodsky Date: Mon, 27 Apr 2026 13:03:33 +0100 Subject: [PATCH v2 1/5] arm64: signal: Preserve POR_EL0 if poe_context is missing Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260427-poe_signal-v2-1-2bd9d6f16ab4@arm.com> References: <20260427-poe_signal-v2-0-2bd9d6f16ab4@arm.com> In-Reply-To: <20260427-poe_signal-v2-0-2bd9d6f16ab4@arm.com> To: linux-arm-kernel@lists.infradead.org Cc: Kevin Brodsky , Andrew Morton , Catalin Marinas , "David Hildenbrand (Arm)" , Joey Gouly , Mark Brown , Shuah Khan , Will Deacon , linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1777291437; l=5608; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=slrafw9MOFyBo/v8zwX3peiajbdJyOH74VvtDwDB9UQ=; b=MVsLaSQUtzBk2Ysh4JQTsUjt2XFmOZOJwMNMNpWEaLRYmDd/XLhfcN+XZK55TQq7hob0Tic8i xh0wf54gogVBQSsnRVBsRaTMZDoZe+ks2YKFfERfHz6ssnWNIe2zmFS X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= 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. To ensure that __valid_fields is kept in sync, fields (currently just por_el0) are now accessed via accessors and prefixed with __ to discourage direct access. 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 | 54 ++++++++++++++++++++++++++++++++++++---------- 1 file changed, 43 insertions(+), 11 deletions(-) diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 08ffc5a5aea4..38e6fa204c17 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -67,6 +67,9 @@ struct rt_sigframe_user_layout { unsigned long end_offset; }; +#define TERMINATOR_SIZE round_up(sizeof(struct _aarch64_ctx), 16) +#define EXTRA_CONTEXT_SIZE round_up(sizeof(struct extra_context), 16) + /* * Holds any EL0-controlled state that influences unprivileged memory accesses. * This includes both accesses done in userspace and uaccess done in the kernel. @@ -74,13 +77,35 @@ 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 struct should be zero-initialised. Its members should only be accessed + * via the accessors below. __valid_fields tracks which of the fields are valid + * (have been set to some value). */ struct user_access_state { - u64 por_el0; + unsigned int __valid_fields; + u64 __por_el0; }; -#define TERMINATOR_SIZE round_up(sizeof(struct _aarch64_ctx), 16) -#define EXTRA_CONTEXT_SIZE round_up(sizeof(struct extra_context), 16) +#define UA_STATE_HAS_POR_EL0 BIT(0) + +static void set_ua_state_por_el0(struct user_access_state *ua_state, + u64 por_el0) +{ + ua_state->__por_el0 = por_el0; + ua_state->__valid_fields |= UA_STATE_HAS_POR_EL0; +} + +static int get_ua_state_por_el0(const struct user_access_state *ua_state, + u64 *por_el0) +{ + if (ua_state->__valid_fields & UA_STATE_HAS_POR_EL0) { + *por_el0 = ua_state->__por_el0; + return 0; + } + + return -ENOENT; +} /* * Save the user access state into ua_state and reset it to disable any @@ -94,7 +119,7 @@ static void save_reset_user_access_state(struct user_access_state *ua_state) for (int pkey = 0; pkey < arch_max_pkey(); pkey++) por_enable_all |= POR_ELx_PERM_PREP(pkey, POE_RWX); - ua_state->por_el0 = read_sysreg_s(SYS_POR_EL0); + set_ua_state_por_el0(ua_state, read_sysreg_s(SYS_POR_EL0)); write_sysreg_s(por_enable_all, SYS_POR_EL0); /* * No ISB required as we can tolerate spurious Overlay faults - @@ -122,8 +147,10 @@ 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()) - write_sysreg_s(ua_state->por_el0, SYS_POR_EL0); + u64 por_el0; + + if (get_ua_state_por_el0(ua_state, &por_el0) == 0) + write_sysreg_s(por_el0, SYS_POR_EL0); } static void init_user_layout(struct rt_sigframe_user_layout *user) @@ -333,11 +360,16 @@ static int restore_fpmr_context(struct user_ctxs *user) static int preserve_poe_context(struct poe_context __user *ctx, const struct user_access_state *ua_state) { - int err = 0; + int err; + u64 por_el0; + + err = get_ua_state_por_el0(ua_state, &por_el0); + if (WARN_ON_ONCE(err)) + return err; __put_user_error(POE_MAGIC, &ctx->head.magic, err); __put_user_error(sizeof(*ctx), &ctx->head.size, err); - __put_user_error(ua_state->por_el0, &ctx->por_el0, err); + __put_user_error(por_el0, &ctx->por_el0, err); return err; } @@ -353,7 +385,7 @@ static int restore_poe_context(struct user_ctxs *user, __get_user_error(por_el0, &(user->poe->por_el0), err); if (!err) - ua_state->por_el0 = por_el0; + set_ua_state_por_el0(ua_state, por_el0); return err; } @@ -1095,7 +1127,7 @@ 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 = {}; /* Always make any pending restarted system calls return -EINTR */ current->restart_block.fn = do_no_restart_syscall; @@ -1507,7 +1539,7 @@ 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 = {}; int err = 0; fpsimd_save_and_flush_current_state(); -- 2.51.2