diff mbox series

[v3,3/3] x86/Kconfig: introduce option to select retpoline usage

Message ID 20220218143416.34475-4-roger.pau@citrix.com (mailing list archive)
State New, archived
Headers show
Series retpoline: add clang support + Kconfig selectable | expand

Commit Message

Roger Pau Monné Feb. 18, 2022, 2:34 p.m. UTC 
Add a new Kconfig option under the "Speculative hardening" section
that allows selecting whether to enable retpoline. This depends on the
underlying compiler having retpoline support.

Requested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Changes since v2:
 - Place first in the section.
 - Remove "If unsure".

Changes since v1:
 - Fix description of option to use indirect branches instead of
   indirect calls.
---
 xen/arch/x86/Kconfig |  5 -----
 xen/common/Kconfig   | 14 ++++++++++++++
 2 files changed, 14 insertions(+), 5 deletions(-)
diff mbox series

Patch

diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index f8dca4dc85..eb4d1a949f 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -36,11 +36,6 @@  config CC_INDIRECT_THUNK
 	def_bool $(cc-option,-mindirect-branch-register) || \
 	         $(cc-option,-mretpoline-external-thunk)
 
-
-config INDIRECT_THUNK
-	def_bool y
-	depends on CC_INDIRECT_THUNK
-
 config HAS_AS_CET_SS
 	# binutils >= 2.29 or LLVM >= 6
 	def_bool $(as-instr,wrssq %rax$(comma)0;setssbsy)
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index db687b1785..533b8f33e6 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -85,6 +85,20 @@  config STATIC_MEMORY
 
 menu "Speculative hardening"
 
+config INDIRECT_THUNK
+	bool "Speculative Branch Target Injection Protection"
+	depends on CC_INDIRECT_THUNK
+	default y
+	help
+	  Contemporary processors may use speculative execution as a
+	  performance optimisation, but this can potentially be abused by an
+	  attacker to leak data via speculative sidechannels.
+
+	  One source of data leakage is via branch target injection.
+
+	  When enabled, indirect branches are implemented using a new construct
+	  called "retpoline" that prevents speculation.
+
 config SPECULATIVE_HARDEN_ARRAY
 	bool "Speculative Array Hardening"
 	default y