[tip: x86/core] x86/Kconfig: Enable kernel IBT by default

["tip-bot2 for Kees Cook" <tip-bot2@linutronix.de>]

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

Commit-ID:     4fd5f70ce14da230c6a29648c3d51a48ee0b4bfd
Gitweb:        https://git.kernel.org/tip/4fd5f70ce14da230c6a29648c3d51a48ee0b4bfd
Author:        Kees Cook <keescook@chromium.org>
AuthorDate:    Tue, 01 Nov 2022 10:25:07 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Sat, 05 Nov 2022 11:28:03 +01:00

x86/Kconfig: Enable kernel IBT by default

The kernel IBT defense strongly mitigates the common "first step" of ROP
attacks, by eliminating arbitrary stack pivots (that appear either at
the end of a function or in immediate values), which cannot be reached
if indirect calls must be to marked function entry addresses. IBT is
also required to be enabled to gain the FineIBT feature when built with
Kernel Control Flow Integrity.

Additionally, given that this feature is runtime enabled via CPU ID,
it clearly should be built in by default; it will only be enabled if the
CPU supports it. The build takes 2 seconds longer, which seems a small
price to pay for gaining this coverage by default.

Suggested-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20221101172503.gonna.094-kees@kernel.org
---
 arch/x86/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 479ee63..aaf1f0f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1856,7 +1856,7 @@ config CC_HAS_IBT
 
 config X86_KERNEL_IBT
 	prompt "Indirect Branch Tracking"
-	bool
+	def_bool y
 	depends on X86_64 && CC_HAS_IBT && HAVE_OBJTOOL
 	# https://github.com/llvm/llvm-project/commit/9d7001eba9c4cb311e03cd8cdc231f9e579f2d0f
 	depends on !LD_IS_LLD || LLD_VERSION >= 140000