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x86/lam: Disable ADDRESS_MASKING in most cases

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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 <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.1706068222.git.pawan.kumar.gupta%40linux.intel.com
This commit is contained in:
Pawan Gupta 2024-01-23 19:55:21 -08:00 committed by Dave Hansen
parent ffd95846c6
commit 3267cb6d3a
1 changed files with 1 additions and 0 deletions
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arch/x86/Kconfig
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@ -2257,6 +2257,7 @@ config RANDOMIZE_MEMORY_PHYSICAL_PADDING
config ADDRESS_MASKING config ADDRESS_MASKING
bool "Linear Address Masking support" bool "Linear Address Masking support"
depends on X86_64 depends on X86_64
depends on COMPILE_TEST || !CPU_MITIGATIONS # wait for LASS
help help
Linear Address Masking (LAM) modifies the checking that is applied Linear Address Masking (LAM) modifies the checking that is applied
to 64-bit linear addresses, allowing software to use of the to 64-bit linear addresses, allowing software to use of the