From: Roger Pau Monné Date: Thu, 31 Mar 2022 08:57:23 +0000 (+0200) Subject: x86/Kconfig: introduce option to select retpoline usage X-Git-Tag: archive/raspbian/4.16.1-1+rpi1^2~38^2~30 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=dd359f9f505e7df960aad13116bc6f576f5fdd94;p=xen.git x86/Kconfig: introduce option to select retpoline usage 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 Signed-off-by: Roger Pau Monné Acked-by: Andrew Cooper master commit: 95d9ab46143685f169f636cfdd7997e2fc630e86 master date: 2022-02-21 18:17:56 +0000 --- diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig index 34dcb47ecd..3c14096c80 100644 --- a/xen/arch/x86/Kconfig +++ b/xen/arch/x86/Kconfig @@ -36,10 +36,6 @@ config CC_HAS_INDIRECT_THUNK def_bool $(cc-option,-mindirect-branch-register) || \ $(cc-option,-mretpoline-external-thunk) -config INDIRECT_THUNK - def_bool y - depends on CC_HAS_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..6443943889 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_HAS_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