mitigations.7: Describe LASS

Reviewed by:	kib, markj
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55281

This commit is contained in:

Ed Maste

2026-02-13 15:31:51 -05:00

parent f4d1a3ab02

commit b20883e821

1 changed files with 15 additions and 2 deletions

+15 -2

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@@ -335,8 +335,17 @@ Another feature prevents unintended reads from or writes to user space memory
 from the kernel.
 This also provides effective protection against NULL pointer dereferences from
 kernel.
 An additional mechanism,
 Linear Address Space Separation (LASS), is available on some amd64 machines.
 LASS prevents user-mode applications from accessing kernel-mode memory,
 and the kernel from unsanctioned access to userspace memory.
 Unlike page table-based permission controls, LASS is based only on address
 values.
 As a consequence of enforcing this separation in hardware, LASS also provides
 mitigation against certain speculative-execution side-channel attacks.
 .Bl -column -offset indent "Architecture" "Feature" "Access Type Prevented"
 .It Sy Architecture Ta Sy Feature Ta Sy Access Type Prevented
 .It amd64       Ta LASS  Ta All
 .It amd64       Ta SMAP  Ta Read / Write
 .It amd64       Ta SMEP  Ta Execute
 .It arm64       Ta PAN   Ta Read / Write
@@ -345,8 +354,12 @@ kernel.
 .It riscv       Ta -     Ta Execute
 .El
 .Pp
 These features are automatically used by the kernel.
 There is no user-facing configuration.
 Most of these features are automatically used by the kernel,
 with no user-facing configuration.
 LASS is controlled by the
 .Va hw.lass
 loader tunable.
 It is enabled by default, when available.
 .\"
 .Ss Capsicum
 Capsicum is a lightweight OS capability and sandbox framework.