linux-kernel - [PATCH 2/2] x86/Kconfig: Only allow CONFIG_X86_KERNEL

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Date:   Fri, 18 Mar 2022 16:07:47 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH 2/2] x86/Kconfig: Only allow CONFIG_X86_KERNEL_IBT with ld.lld >= 14.0.0

With CONFIG_X86_KERNEL_IBT=y and a version of ld.lld prior to 14.0.0,
there are numerous objtool warnings along the lines of:

  warning: objtool: .plt+0x6: indirect jump found in RETPOLINE build

This is a known issue that has been resolved in ld.lld 14.0.0. Prevent
CONFIG_X86_KERNEL_IBT from being selectable when using one of these
problematic ld.lld versions.

Link: https://github.com/llvm/llvm-project/commit/9d7001eba9c4cb311e03cd8cdc231f9e579f2d0f
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 arch/x86/Kconfig | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 921e4ebda564..87579264aa00 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1875,6 +1875,8 @@ config X86_KERNEL_IBT
 	prompt "Indirect Branch Tracking"
 	bool
 	depends on X86_64 && CC_HAS_IBT && STACK_VALIDATION
+	# https://github.com/llvm/llvm-project/commit/9d7001eba9c4cb311e03cd8cdc231f9e579f2d0f
+	depends on !LD_IS_LLD || LLD_VERSION >= 140000
 	help
 	  Build the kernel with support for Indirect Branch Tracking, a
 	  hardware support course-grain forward-edge Control Flow Integrity
-- 
2.35.1