From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 A39BC376449; Mon, 5 May 2025 22:48:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746485333; cv=none; b=ZKiOzf0acziBxiiZKQmvmdIl0sMJZm+AGDqVr22F0VhcyBjJVZuTjUHtPvdveZvSWTpZvP28ecx0L1j38Ptvv3pcZu0bjtD6oc6UPlkjrZhzVzNcCdW1KsH/g22CROQxzU3jXf8UsR+7EikbZ837XJzdKwxKZRuRyWTA/YTkQ/I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746485333; c=relaxed/simple; bh=c1/2qQCsV/F3YVMiDB6OB5XkR6nW22zqR29RCrTEh2U=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=hYIqO6VrVNeqkmvwASO0Sp0kFv/t2CYa2QJI9qqTV9wbJJEHdbwk7mkLgU+6rtriOgdXTTu6rTXgaaLuKHW0hscYIlMjF0iZR2EAZkCKHfI/lhgOEz5c6B9G7KQEEFResndSK+YPed8QDj9ixdFuk9hxjfzfWLnBV/MZx9Wr63U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lR+KUTHn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lR+KUTHn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E58A2C4CEEF; Mon, 5 May 2025 22:48:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746485332; bh=c1/2qQCsV/F3YVMiDB6OB5XkR6nW22zqR29RCrTEh2U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lR+KUTHnJ4hhv/1VgOxZWWUnGHvofNKokHSx6edSQAbzBAVFwy/NdfjKIe5uezOvU PdOFdj50Ocs2yxa87LhMzv2jygdE4k7tQiASb9wL9a3FuwmKCaZBck5yzVs8yLHdvg BzQUo354UDGOapdbmZNdt5IO4otlaB93VXq4xqBOqveTI/QCky4Df4GiesCJgakBw4 +7qJrE5a+qIIJHtSt/o3FD6me1F4J0yA9S/fbCHSDNN7hq0ZWKnAz+lLBrtxmshh3d mlsLd9ygIJH/r9ODS2pPPM53mfRjguAp5739k4eG6mxgA+WrEfx7dOs1XcjxlAbiZR MHXNLlt9wZkEg== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Balbir Singh , Ingo Molnar , Kees Cook , Bjorn Helgaas , Linus Torvalds , Peter Zijlstra , Andy Lutomirski , Sasha Levin , dave.hansen@linux.intel.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, linux-pci@vger.kernel.org Subject: [PATCH AUTOSEL 6.12 271/486] x86/kaslr: Reduce KASLR entropy on most x86 systems Date: Mon, 5 May 2025 18:35:47 -0400 Message-Id: <20250505223922.2682012-271-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250505223922.2682012-1-sashal@kernel.org> References: <20250505223922.2682012-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.12.26 Content-Transfer-Encoding: 8bit From: Balbir Singh [ Upstream commit 7ffb791423c7c518269a9aad35039ef824a40adb ] When CONFIG_PCI_P2PDMA=y (which is basically enabled on all large x86 distros), it maps the PFN's via a ZONE_DEVICE mapping using devm_memremap_pages(). The mapped virtual address range corresponds to the pci_resource_start() of the BAR address and size corresponding to the BAR length. When KASLR is enabled, the direct map range of the kernel is reduced to the size of physical memory plus additional padding. If the BAR address is beyond this limit, PCI peer to peer DMA mappings fail. Fix this by not shrinking the size of the direct map when CONFIG_PCI_P2PDMA=y. This reduces the total available entropy, but it's better than the current work around of having to disable KASLR completely. [ mingo: Clarified the changelog to point out the broad impact ... ] Signed-off-by: Balbir Singh Signed-off-by: Ingo Molnar Reviewed-by: Kees Cook Acked-by: Bjorn Helgaas # drivers/pci/Kconfig Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Andy Lutomirski Link: https://lore.kernel.org/lkml/20250206023201.1481957-1-balbirs@nvidia.com/ Link: https://lore.kernel.org/r/20250206234234.1912585-1-balbirs@nvidia.com -- arch/x86/mm/kaslr.c | 10 ++++++++-- drivers/pci/Kconfig | 6 ++++++ 2 files changed, 14 insertions(+), 2 deletions(-) Signed-off-by: Sasha Levin --- arch/x86/mm/kaslr.c | 10 ++++++++-- drivers/pci/Kconfig | 6 ++++++ 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 230f1dee4f095..e0b0ec0f82457 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -109,8 +109,14 @@ void __init kernel_randomize_memory(void) memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) + CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING; - /* Adapt physical memory region size based on available memory */ - if (memory_tb < kaslr_regions[0].size_tb) + /* + * Adapt physical memory region size based on available memory, + * except when CONFIG_PCI_P2PDMA is enabled. P2PDMA exposes the + * device BAR space assuming the direct map space is large enough + * for creating a ZONE_DEVICE mapping in the direct map corresponding + * to the physical BAR address. + */ + if (!IS_ENABLED(CONFIG_PCI_P2PDMA) && (memory_tb < kaslr_regions[0].size_tb)) kaslr_regions[0].size_tb = memory_tb; /* diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig index 0d94e4a967d81..7cef00d9d7ab6 100644 --- a/drivers/pci/Kconfig +++ b/drivers/pci/Kconfig @@ -194,6 +194,12 @@ config PCI_P2PDMA P2P DMA transactions must be between devices behind the same root port. + Enabling this option will reduce the entropy of x86 KASLR memory + regions. For example - on a 46 bit system, the entropy goes down + from 16 bits to 15 bits. The actual reduction in entropy depends + on the physical address bits, on processor features, kernel config + (5 level page table) and physical memory present on the system. + If unsure, say N. config PCI_LABEL -- 2.39.5