linux-kernel - [PATCH v3 29/31] arm: Implement thread_struct whitelist for hardened usercopy

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Date:   Wed, 20 Sep 2017 13:45:35 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...nel.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, kernel-hardening@...ts.openwall.com,
        David Windsor <dave@...lcore.net>
Subject: [PATCH v3 29/31] arm: Implement thread_struct whitelist for hardened usercopy

ARM does not carry FPU state in the thread structure, so it can declare
no usercopy whitelist at all.

Cc: Russell King <linux@...linux.org.uk>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: linux-arm-kernel@...ts.infradead.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm/Kconfig                 | 1 +
 arch/arm/include/asm/processor.h | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 7888c9803eb0..4f1ab6c6b8c0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -48,6 +48,7 @@ config ARM
 	select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
 	select HAVE_ARCH_MMAP_RND_BITS if MMU
 	select HAVE_ARCH_SECCOMP_FILTER if (AEABI && !OABI_COMPAT)
+	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARM_SMCCC if CPU_V7
 	select HAVE_EBPF_JIT if !CPU_ENDIAN_BE32
diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index c3d5fc124a05..d6dc45c92ee5 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -45,6 +45,13 @@ struct thread_struct {
 	struct debug_info	debug;
 };
 
+/* Nothing needs to be usercopy-whitelisted from thread_struct. */
+static inline void arch_thread_struct_whitelist(unsigned long *offset,
+						unsigned long *size)
+{
+	*offset = *size = 0;
+}
+
 #define INIT_THREAD  {	}
 
 #ifdef CONFIG_MMU
-- 
2.7.4