[PATCH] x86/lam: Disable ADDRESS_MASKING in most cases

[Pawan Gupta]

Intel feature 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.

[1] SLAM: https://download.vusec.net/papers/slam_sp24.pdf
[2] LASS: https://lore.kernel.org/lkml/20230609183632.48706-1-alexander.shishkin@xxxxxxxxxxxxxxx/

Cc: stable@xxxxxxxxxxxxxxx # v6.4+
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
---
 arch/x86/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1566748f16c4..794517df8068 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2270,6 +2270,7 @@ config RANDOMIZE_MEMORY_PHYSICAL_PADDING
 config ADDRESS_MASKING
 	bool "Linear Address Masking support"
 	depends on X86_64
+	depends on COMPILE_TEST || !SPECULATION_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

base-commit: 0dd3ee31125508cd67f7e7172247f05b7fd1753a
-- 
2.34.1