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 6994A478E20 for ; Tue, 18 Aug 2026 14:11:57 +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=1787062319; cv=none; b=jpPSzBQXjm5FxipXP47tFFoO0DHPAAafQX/u+3A414/nqAO2uNrycPzV86mxj2bNZzpKVxIWISu882lKq/JhnTRIEKY1IvWL+yOtG9tQpEuEdfiCspF+skfhx1hpRoXkDkNpIoFPW+A3weYEeLsfa5rHGMyjIcFyjleAgs53pn4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787062319; c=relaxed/simple; bh=OUd9tIsUKUmYmJFdd7bshHjQNhEMzbzjXfpa96AJHgY=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=VrYv+KpVrxbDYQw8MTZagr4r5H66K2zK4ws4pgcKSP2ON5l5a5tGA21z4egP2MoeYbvM3IYG711sukMu9mTlZaUR/+Rnm0ClvfWQKKrrGJr75dElTvYs/EOGq8DKoXK/EaGp6kZ30Rn19YXp0JrefTuwftb8Mt+HBTA+b4iNIlA= 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=qmujkZbp; 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="qmujkZbp" 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 0D6A719F0; Tue, 18 Aug 2026 07:11:53 -0700 (PDT) Received: from localhost.localdomain (e123572-lin.cambridge.arm.com [10.2.208.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4BD3C3F85F; Tue, 18 Aug 2026 07:11:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1787062316; bh=OUd9tIsUKUmYmJFdd7bshHjQNhEMzbzjXfpa96AJHgY=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=qmujkZbpTeTsmrHyAf/qaEa8Nq7dlkfqj+c/vKoIikQ0V06rSh9KrR/pRLcrW9ffA z29nV5viUQ3wGoB26WNlwwpAhFgAQpOrGvK6mdY7MyQU+GKtvm2AnSUtM9lM+02aPm YKHFOlZVngpDxQ3rff18JdR/LmnFYPty2cYgms/U= From: Kevin Brodsky Date: Tue, 18 Aug 2026 15:08:49 +0100 Subject: [PATCH RFC v9 07/25] arm64: Context-switch POR_EL1 Precedence: bulk X-Mailing-List: linux-hardening@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: <20260818-kpkeys-v9-7-743ad31b2c8f@arm.com> References: <20260818-kpkeys-v9-0-743ad31b2c8f@arm.com> In-Reply-To: <20260818-kpkeys-v9-0-743ad31b2c8f@arm.com> To: linux-hardening@vger.kernel.org Cc: Kevin Brodsky , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , "David Hildenbrand (Arm)" , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linu Cherian , Linus Walleij , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , =?utf-8?q?Pierre-Cl=C3=A9ment_Tosi?= , Quentin Perret , Rick Edgecombe , Ryan Roberts , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org, Ira Weiny , Lorenzo Stoakes , Thomas Gleixner X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787062276; l=2038; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=OUd9tIsUKUmYmJFdd7bshHjQNhEMzbzjXfpa96AJHgY=; b=mPluEjZtRsLQjo5bC+3nVcrHgi0+Q8vudQwS8etOmxj8McFohmUhLrEF/NL095tJxHzNpqP0V w/2lu2NlSCGCkCU9ak+BuaVIwfPAHqw5s71plqinBt9CylKiS/K4bT0 X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= POR_EL1 is about to be used by the kpkeys framework, modifying it for (typically small) sections of code. If an exception occurs during that window and scheduling occurs, we must ensure that POR_EL1 is context-switched as needed (saving the old value and restoring the new one). An ISB is needed to ensure the write takes effect, so we skip it if the new value is the same as the old, like for POR_EL0. Signed-off-by: Kevin Brodsky --- arch/arm64/include/asm/processor.h | 1 + arch/arm64/kernel/process.c | 10 ++++++++++ 2 files changed, 11 insertions(+) diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index c2a627f39314..8d7fa479cd36 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -195,6 +195,7 @@ struct thread_struct { u64 svcr; u64 tpidr2_el0; u64 por_el0; + u64 por_el1; #ifdef CONFIG_ARM64_GCS unsigned int gcs_el0_mode; unsigned int gcs_el0_locked; diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 581f80e9b9b7..1dec143decf1 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -51,6 +51,7 @@ #include #include #include +#include #include #include #include @@ -431,6 +432,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) ptrauth_thread_init_kernel(p); + if (system_supports_poe()) + p->thread.por_el1 = POR_EL1_INIT; + if (likely(!args->fn)) { *childregs = *current_pt_regs(); childregs->regs[0] = 0; @@ -681,6 +685,12 @@ static void permission_overlay_switch(struct task_struct *next) * of POR_EL0. */ } + + current->thread.por_el1 = read_sysreg_s(SYS_POR_EL1); + if (current->thread.por_el1 != next->thread.por_el1) { + write_sysreg_s(next->thread.por_el1, SYS_POR_EL1); + isb(); + } } /* -- 2.51.2