Re: [PATCH v5 16/16] Revert "x86/lam: Disable ADDRESS_MASKING in most cases"

From: Kirill A. Shutemov
Date: Mon Oct 28 2024 - 16:42:32 EST


On Mon, Oct 28, 2024 at 06:08:04PM +0200, Alexander Shishkin wrote:
> This reverts commit 3267cb6d3a174ff83d6287dcd5b0047bbd912452.
>
> LASS mitigates the Spectre based on LAM (SLAM) [1] and an earlier
> commit made LAM depend on LASS, so we no longer need to disable LAM at
> compile time, so revert the commit that disables LAM.
>
> [1] https://download.vusec.net/papers/slam_sp24.pdf
>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> CC: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>

Before re-enabling LAM, you need to uncomment X86_FEATURE_LAM check in
arch/x86/kernel/cpu/common.c introduced in recent 86e6b1547b3d ("x86: fix
user address masking non-canonical speculation issue").

--
Kiryl Shutsemau / Kirill A. Shutemov