From 60a5ba560f296ad8da153f6ad3f70030bfa3958f Mon Sep 17 00:00:00 2001 From: Pawan Gupta Date: Tue, 23 Jan 2024 19:55:21 -0800 Subject: [PATCH] x86/lam: Disable ADDRESS_MASKING in most cases commit 3267cb6d3a174ff83d6287dcd5b0047bbd912452 upstream. Linear Address Masking (LAM) has a weakness related to transient execution as described in the SLAM paper[1]. Unless Linear Address Space Separation (LASS) is enabled this weakness may be exploitable. Until kernel adds support for LASS[2], only allow LAM for COMPILE_TEST, or when speculation mitigations have been disabled at compile time, otherwise keep LAM disabled. There are no processors in market that support LAM yet, so currently nobody is affected by this issue. [1] SLAM: https://download.vusec.net/papers/slam_sp24.pdf [2] LASS: https://lore.kernel.org/lkml/20230609183632.48706-1-alexander.shishkin@linux.intel.com/ [ dhansen: update SPECULATION_MITIGATIONS -> CPU_MITIGATIONS ] Signed-off-by: Pawan Gupta Signed-off-by: Dave Hansen Reviewed-by: Sohil Mehta Acked-by: Kirill A. Shutemov Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/5373262886f2783f054256babdf5a98545dc986b.1706068222.git.pawan.kumar.gupta%40linux.intel.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 82d12c93feab..05c82fd5d0f6 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2217,6 +2217,7 @@ config RANDOMIZE_MEMORY_PHYSICAL_PADDING config ADDRESS_MASKING bool "Linear Address Masking support" depends on X86_64 + depends on COMPILE_TEST || !CPU_MITIGATIONS # wait for LASS help Linear Address Masking (LAM) modifies the checking that is applied to 64-bit linear addresses, allowing software to use of the