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Tue, 06 Mar 2018 03:22:49 -0800 (PST) Date: Tue, 6 Mar 2018 20:22:41 +0900 From: Jinbum Park To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH] arm: mm: Kconfig: Disable KUSER_HELPERS in ARMv6 or later as default Message-ID: <20180306112241.GA5938@pjb1027-Latitude-E5410> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180306_032302_495862_2FCE1944 X-CRM114-Status: GOOD ( 12.39 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, vladimir.murzin@arm.com, keescook@chromium.org, gregkh@linuxfoundation.org, will.deacon@arm.com, catalin.marinas@arm.com Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Codes for KUSER_HELPERS can be abused as ROP gadaget, So that It's better to disable that as if possible. Since over ARMv6 has ldrex/strex at user-space, NEED_KUSER_HELPERS is not selected for over ARMv6. But, Even though NEED_KUSER_HELPERS is not selected, current configuration enable KUSER_HELPERS as default. * as-is - Enable KUSER_HELPERS as default even though over ARMv6. - User can disable KUSER_HELPERS. * to-be - Disable KUSER_HELPERS in ARMv6 or later as default. - User can enable KUSER_HELPERS for compatibility. This change removes the unnecessary configuration that has security-risk. Signed-off-by: Jinbum Park --- arch/arm/mm/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig index 7f14acf..40e5fe5 100644 --- a/arch/arm/mm/Kconfig +++ b/arch/arm/mm/Kconfig @@ -840,7 +840,7 @@ config NEED_KUSER_HELPERS config KUSER_HELPERS bool "Enable kuser helpers in vector page" if !NEED_KUSER_HELPERS depends on MMU - default y + default y if NEED_KUSER_HELPERS help Warning: disabling this option may break user programs.