The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 3267cb6d3a174ff83d6287dcd5b0047bbd912452 Gitweb: https://git.kernel.org/tip/3267cb6d3a174ff83d6287dcd5b0047bbd912452 Author: Pawan Gupta pawan.kumar.gupta@linux.intel.com AuthorDate: Tue, 23 Jan 2024 19:55:21 -08:00 Committer: Dave Hansen dave.hansen@linux.intel.com CommitterDate: Mon, 21 Oct 2024 15:05:43 -07:00

x86/lam: Disable ADDRESS_MASKING in most cases

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...

[ dhansen: update SPECULATION_MITIGATIONS -> CPU_MITIGATIONS ]

Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Reviewed-by: Sohil Mehta sohil.mehta@intel.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/5373262886f2783f054256babdf5a98545dc986b.1706068... --- arch/x86/Kconfig | 1 + 1 file changed, 1 insertion(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 2852fcd..16354df 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2257,6 +2257,7 @@ 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