From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 35C8744CF37; Tue, 16 Jun 2026 16:16:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781626589; cv=none; b=D3zN4/kILrgSlwLapJIMg6DIPdHJkQqUwptqBnk0vwKNOLInBHk2UjhL/mUvXDjOwY17xc27qQNUojXc3KuPxC7EJ5w/X7lVw8si5MC5XXJ+omJGphTyDmRbt4zufKZLXQAQVxVrAwtWcvWbCFY+3U67qHUYIWgJbwIU9N5GZdI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781626589; c=relaxed/simple; bh=tcWfVe85J0hVSd5zdT7XiHkiWOM75gaobQx8IxPLPMA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=X+j9P5f9KRZm551nVX+8HLPa9ZertxDboj43kd1Fgt/9KInh2V8FYjkSJ6Z8mFTV7Ww3y0rH/aJLnDGXSQ8D9f9K4kyakRQKQBPYkxzS9r/yXDdTfDSQam/qsAbXqxGukEXyJMNdnc3V2374DJ+WOtPyj3paX6qlmnZgKijqr0c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Q96KC2xI; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Q96KC2xI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ED8481F000E9; Tue, 16 Jun 2026 16:16:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781626587; bh=T7vsuJO6JPkkHAqvCCM2iDtqOgZKAGbJIV5z3s5IMIg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Q96KC2xIAPeuAEiv4vHTJzbvBsEgpRKw8TP+TvGb0I+9ykQFcKw4mx1n0N24mnYeg el0JL8Yns4fHQcxLgg99p5Em8ibX2CQBCAp/HcL9yM7/ojQ/n2dAtNHqOdgeU2aSeO 4PBdp/OgNPhfR3dHVXDk6nTwxPi8a/V5GH4CGzCA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Xie Yuanbin , "Russell King (Oracle)" , Sebastian Andrzej Siewior , Sasha Levin Subject: [PATCH 6.12 006/261] ARM: fix branch predictor hardening Date: Tue, 16 Jun 2026 20:27:24 +0530 Message-ID: <20260616145045.314806480@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145044.869532709@linuxfoundation.org> References: <20260616145044.869532709@linuxfoundation.org> User-Agent: quilt/0.69 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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Russell King (Oracle) commit fd2dee1c6e2256f726ba33fd3083a7be0efc80d3 upstream. __do_user_fault() may be called with indeterminent interrupt enable state, which means we may be preemptive at this point. This causes problems when calling harden_branch_predictor(). For example, when called from a data abort, do_alignment_fault()->do_bad_area(). Move harden_branch_predictor() out of __do_user_fault() and into the calling contexts. Moving it into do_kernel_address_page_fault(), we can be sure that interrupts will be disabled here. Converting do_translation_fault() to use do_kernel_address_page_fault() rather than do_bad_area() means that we keep branch predictor handling for translation faults. Interrupts will also be disabled at this call site. do_sect_fault() needs special handling, so detect user mode accesses to kernel-addresses, and add an explicit call to branch predictor hardening. Finally, add branch predictor hardening to do_alignment() for the faulting case (user mode accessing kernel addresses) before interrupts are enabled. This should cover all cases where harden_branch_predictor() is called, ensuring that it is always has interrupts disabled, also ensuring that it is called early in each call path. Reviewed-by: Xie Yuanbin Tested-by: Xie Yuanbin Signed-off-by: Russell King (Oracle) Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Sasha Levin --- arch/arm/mm/alignment.c | 6 +++++- arch/arm/mm/fault.c | 39 ++++++++++++++++++++++++++------------- 2 files changed, 31 insertions(+), 14 deletions(-) diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c index 3c6ddb1afdc463..812380f30ae36a 100644 --- a/arch/arm/mm/alignment.c +++ b/arch/arm/mm/alignment.c @@ -19,10 +19,11 @@ #include #include #include +#include #include #include -#include +#include #include #include "fault.h" @@ -809,6 +810,9 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs) int thumb2_32b = 0; int fault; + if (addr >= TASK_SIZE && user_mode(regs)) + harden_branch_predictor(); + if (interrupts_enabled(regs)) local_irq_enable(); diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c index 8768c70fd885bc..16b5a7d214808f 100644 --- a/arch/arm/mm/fault.c +++ b/arch/arm/mm/fault.c @@ -199,9 +199,6 @@ __do_user_fault(unsigned long addr, unsigned int fsr, unsigned int sig, { struct task_struct *tsk = current; - if (addr > TASK_SIZE) - harden_branch_predictor(); - #ifdef CONFIG_DEBUG_USER if (((user_debug & UDBG_SEGV) && (sig == SIGSEGV)) || ((user_debug & UDBG_BUS) && (sig == SIGBUS))) { @@ -270,8 +267,10 @@ do_kernel_address_page_fault(struct mm_struct *mm, unsigned long addr, /* * Fault from user mode for a kernel space address. User mode * should not be faulting in kernel space, which includes the - * vector/khelper page. Send a SIGSEGV. + * vector/khelper page. Handle the branch predictor hardening + * while interrupts are still disabled, then send a SIGSEGV. */ + harden_branch_predictor(); __do_user_fault(addr, fsr, SIGSEGV, SEGV_MAPERR, regs); } else { /* @@ -486,16 +485,20 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs) * We enter here because the first level page table doesn't contain * a valid entry for the address. * - * If the address is in kernel space (>= TASK_SIZE), then we are - * probably faulting in the vmalloc() area. + * If this is a user address (addr < TASK_SIZE), we handle this as a + * normal page fault. This leaves the remainder of the function to handle + * kernel address translation faults. * - * If the init_task's first level page tables contains the relevant - * entry, we copy the it to this task. If not, we send the process - * a signal, fixup the exception, or oops the kernel. + * Since user mode is not permitted to access kernel addresses, pass these + * directly to do_kernel_address_page_fault() to handle. * - * NOTE! We MUST NOT take any locks for this case. We may be in an - * interrupt or a critical region, and should only copy the information - * from the master page table, nothing more. + * Otherwise, we're probably faulting in the vmalloc() area, so try to fix + * that up. Note that we must not take any locks or enable interrupts in + * this case. + * + * If vmalloc() fixup fails, that means the non-leaf page tables did not + * contain an entry for this address, so handle this via + * do_kernel_address_page_fault(). */ #ifdef CONFIG_MMU static int __kprobes @@ -561,7 +564,8 @@ do_translation_fault(unsigned long addr, unsigned int fsr, return 0; bad_area: - do_bad_area(addr, fsr, regs); + do_kernel_address_page_fault(current->mm, addr, fsr, regs); + return 0; } #else /* CONFIG_MMU */ @@ -581,7 +585,16 @@ do_translation_fault(unsigned long addr, unsigned int fsr, static int do_sect_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs) { + /* + * If this is a kernel address, but from user mode, then userspace + * is trying bad stuff. Invoke the branch predictor handling. + * Interrupts are disabled here. + */ + if (addr >= TASK_SIZE && user_mode(regs)) + harden_branch_predictor(); + do_bad_area(addr, fsr, regs); + return 0; } #endif /* CONFIG_ARM_LPAE */ -- 2.53.0