[tip: x86/core] x86/Kconfig: Add CONFIG_CALL_THUNKS

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     8f7c0d8b23c3f5f740a48db31ebadef28af17a22
Gitweb:        https://git.kernel.org/tip/8f7c0d8b23c3f5f740a48db31ebadef28af17a22
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Thu, 15 Sep 2022 13:11:17 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 17 Oct 2022 16:41:10 +02:00

x86/Kconfig: Add CONFIG_CALL_THUNKS

In preparation for mitigating the Intel SKL RSB underflow issue in
software, add a new configuration symbol which allows to build the
required call thunk infrastructure conditionally.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220915111146.849523555@xxxxxxxxxxxxx
---
 arch/x86/Kconfig | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f408fa8..e18963e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2446,6 +2446,14 @@ config CC_HAS_SLS
 config CC_HAS_RETURN_THUNK
 	def_bool $(cc-option,-mfunction-return=thunk-extern)
 
+config HAVE_CALL_THUNKS
+	def_bool y
+	depends on RETHUNK && OBJTOOL
+
+config CALL_THUNKS
+	def_bool n
+	select FUNCTION_ALIGNMENT_16B
+
 menuconfig SPECULATION_MITIGATIONS
 	bool "Mitigations for speculative execution vulnerabilities"
 	default y