linux-kernel - [PATCH v10 13/13] arm64: BTI: Add Kconfig entry for userspace BTI

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Message-Id: <20200316165055.31179-14-broonie@kernel.org>
Date:   Mon, 16 Mar 2020 16:50:55 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Paul Elliott <paul.elliott@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Amit Kachhap <amit.kachhap@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Marc Zyngier <maz@...nel.org>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        "H . J . Lu " <hjl.tools@...il.com>,
        Andrew Jones <drjones@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Florian Weimer <fweimer@...hat.com>,
        Sudakshina Das <sudi.das@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Dave Martin <Dave.Martin@....com>,
        Mark Brown <broonie@...nel.org>
Subject: [PATCH v10 13/13] arm64: BTI: Add Kconfig entry for userspace BTI

From: Dave Martin <Dave.Martin@....com>

Now that the code for userspace BTI support is in the kernel add the
Kconfig entry so that it can be built and used.

[Split out of "arm64: Basic Branch Target Identification support"
    -- broonie]

Signed-off-by: Dave Martin <Dave.Martin@....com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/Kconfig | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 8a15bc68dadd..d65d226a77ec 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1522,6 +1522,28 @@ endmenu
 
 menu "ARMv8.5 architectural features"
 
+config ARM64_BTI
+	bool "Branch Target Identification support"
+	default y
+	help
+	  Branch Target Identification (part of the ARMv8.5 Extensions)
+	  provides a mechanism to limit the set of locations to which computed
+	  branch instructions such as BR or BLR can jump.
+
+	  To make use of BTI on CPUs that support it, say Y.
+
+	  BTI is intended to provide complementary protection to other control
+	  flow integrity protection mechanisms, such as the Pointer
+	  authentication mechanism provided as part of the ARMv8.3 Extensions.
+	  For this reason, it does not make sense to enable this option without
+	  also enabling support for pointer authentication.  Thus, when
+	  enabling this option you should also select ARM64_PTR_AUTH=y.
+
+	  Userspace binaries must also be specifically compiled to make use of
+	  this mechanism.  If you say N here or the hardware does not support
+	  BTI, such binaries can still run, but you get no additional
+	  enforcement of branch destinations.
+
 config ARM64_E0PD
 	bool "Enable support for E0PD"
 	default y
-- 
2.20.1