linux-kernel - [tip: x86/urgent] x86/lam: Disable ADDRESS

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Message-ID: <172954896978.1442.12851270945186118443.tip-bot2@tip-bot2>
Date: Mon, 21 Oct 2024 22:16:09 -0000
From: "tip-bot2 for Pawan Gupta" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Sohil Mehta <sohil.mehta@...el.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 stable@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/lam: Disable ADDRESS_MASKING in most cases

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@...ux.intel.com>
AuthorDate:    Tue, 23 Jan 2024 19:55:21 -08:00
Committer:     Dave Hansen <dave.hansen@...ux.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.intel.com/

[ dhansen: update SPECULATION_MITIGATIONS -> CPU_MITIGATIONS ]

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Sohil Mehta <sohil.mehta@...el.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc:stable@...r.kernel.org
Link: https://lore.kernel.org/all/5373262886f2783f054256babdf5a98545dc986b.1706068222.git.pawan.kumar.gupta%40linux.intel.com
---
 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