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 3E082353A68; Thu, 2 Jul 2026 16:45:27 +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=1783010728; cv=none; b=WUBka32gUkBMtDKXF+QX7dAFXVoHTzpHSdJtY2ejEJnCjd+iuQzuue57vyLw6+cAjCneUZ//aVk8FvCJqPJUkdd5Wn1AZywR92M3Qkxw+shH/Q01oBHSoeSBXhk+9nhsu/krzTGek0F0xQnhb4FAZn8u8cG5xGUW0DJrSsMR3dA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783010728; c=relaxed/simple; bh=sflJeWuR27vk/9V537wtU4iSx22pJz1h8sGsQOIg5U4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JZCsQGPe0Y5Gg1o1o1hzFeke60F7+iHCNlJwd9xnu/t5FwkdNYpJZ/7apZaMiIIZyI5KjQDPuH+G9gX5RwWzuJikmtywGgw08K8ovQn7gyKBw+EyNx6R04ozn8+bmPOWF34V9cg54O7m017xpCEJ2W6DPg6JzyNtDejuWBukWqM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=TCdEN5rM; 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="TCdEN5rM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A50F21F000E9; Thu, 2 Jul 2026 16:45:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1783010727; bh=H8pAIU99Ugc0wj9gZuVuPMdoXK9exP+8GU+syghucSY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=TCdEN5rMdA/4owU8cVBjR9QmG3xVN/hZS2fBmRgAIgrXN/QO8lR2kdv2ju6ShAwaL 2pAY9erfUZXPhAt1PeRsufH+W3K+KMwOPPorIl6oWLMGavgUTjmKv5VhLfuBEm9XMd ADEE3OVDoi4Wk0S2X9+wXhpmt/grXIAB1uFYIM0o= 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 6.6 015/175] ARM: fix branch predictor hardening Date: Thu, 2 Jul 2026 18:18:36 +0200 Message-ID: <20260702155116.096904554@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260702155115.766838875@linuxfoundation.org> References: <20260702155115.766838875@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 6.6-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 | 4 ++++ arch/arm/mm/fault.c | 39 ++++++++++++++++++++++++++------------- 2 files changed, 30 insertions(+), 13 deletions(-) diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c index f8dd0b3cc8e040..ee264737be6d26 100644 --- a/arch/arm/mm/alignment.c +++ b/arch/arm/mm/alignment.c @@ -22,6 +22,7 @@ #include #include +#include #include #include @@ -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 47eecdf29a8312..87ed5da30e44f1 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))) { @@ -252,8 +249,10 @@ 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 { /* @@ -423,16 +422,20 @@ 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 @@ -498,7 +501,8 @@ 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 */ @@ -518,7 +522,16 @@ 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