From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Garnier Date: Mon, 10 Apr 2017 13:07:56 -0700 Message-Id: <20170410200756.15945-1-thgarnie@google.com> In-Reply-To: <20170410171240.GE30647@e104818-lin.cambridge.arm.com> References: <20170410171240.GE30647@e104818-lin.cambridge.arm.com> Subject: [kernel-hardening] [PATCH v7 4/4] arm64/syscalls: Architecture specific pre-usermode check List-Archive: List-Post: To: Martin Schwidefsky , Heiko Carstens , Arnd Bergmann , Dave Hansen , Andrew Morton , Thomas Garnier , David Howells , =?UTF-8?q?Ren=C3=A9=20Nyffenegger?= , "Paul E . McKenney" , Ingo Molnar , Thomas Gleixner , Oleg Nesterov , Stephen Smalley , Pavel Tikhomirov , Ingo Molnar , "H . Peter Anvin" , Andy Lutomirski , Paolo Bonzini , Kees Cook , Rik van Riel , Josh Poimboeuf , Borislav Petkov , Brian Gerst , "Kirill A . Shutemov" , Christian Borntraeger , Russell King , Will Deacon , Catalin Marinas , Mark Rutland , James Morse Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, kernel-hardening@lists.openwall.com List-ID: Disable the generic pre-usermode check in favor of an optimized implementation. This patch adds specific checks on user-mode return path to make it faster and smaller. The address limit is checked on each syscall return path to user-mode. If it was changed, a generic handler is called to stop the kernel on an explicit check. Signed-off-by: Thomas Garnier Reviewed-by: Catalin Marinas --- Based on next-20170410 Fix comments from Catalin and add review-by in the message. --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/entry.S | 12 ++++++++++++ 2 files changed, 13 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 9b8fcab7da56..3f9e8e7d9376 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -24,6 +24,7 @@ config ARM64 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION select ARCH_WANT_FRAME_POINTERS select ARCH_HAS_UBSAN_SANITIZE_ALL + select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE select ARM_AMBA select ARM_ARCH_TIMER select ARM_GIC diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 43512d4d7df2..04c44c6f41b1 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -744,6 +744,8 @@ ENDPROC(cpu_switch_to) ret_fast_syscall: disable_irq // disable interrupts str x0, [sp, #S_X0] // returned x0 + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change + tbnz x2, #63, addr_limit_fail ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing and x2, x1, #_TIF_SYSCALL_WORK cbnz x2, ret_fast_syscall_trace @@ -771,6 +773,8 @@ work_pending: */ ret_to_user: disable_irq // disable interrupts + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change + tbnz x2, #63, addr_limit_fail ldr x1, [tsk, #TSK_TI_FLAGS] and x2, x1, #_TIF_WORK_MASK cbnz x2, work_pending @@ -780,6 +784,14 @@ finish_ret_to_user: ENDPROC(ret_to_user) /* + * Address limit was incorrect before returning in user-mode which could be + * used to elevate privileges. Call the generic handler to stop the kernel on + * the appropriate check. This function does not return. + */ +addr_limit_fail: + b address_limit_check_failed + +/* * This is how we return from a fork. */ ENTRY(ret_from_fork) -- 2.12.2.715.g7642488e1d-goog