linux-kernel - [tip: x86/core] x86/Kconfig: Only allow CONFIG_X86_KERNEL

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Date:   Tue, 22 Mar 2022 20:23:59 -0000
From:   "tip-bot2 for Nathan Chancellor" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Nathan Chancellor <nathan@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/core] x86/Kconfig: Only allow CONFIG_X86_KERNEL_IBT with
 ld.lld >= 14.0.0

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

Commit-ID:     f6a2c2b2de817078ac5a7e58c10e746165e7825d
Gitweb:        https://git.kernel.org/tip/f6a2c2b2de817078ac5a7e58c10e746165e7825d
Author:        Nathan Chancellor <nathan@...nel.org>
AuthorDate:    Fri, 18 Mar 2022 16:07:47 -07:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 22 Mar 2022 21:12:13 +01:00

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.

Signed-off-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20220318230747.3900772-3-nathan@kernel.org
---
 arch/x86/Kconfig | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 921e4eb..8757926 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