linux-kernel - [PATCH v3 28/31] arm64: Implement thread_struct whitelist for hardened usercopy

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Date:   Wed, 20 Sep 2017 13:45:34 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        James Morse <james.morse@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Dave Martin <Dave.Martin@....com>, zijun_hu <zijun_hu@....com>,
        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 28/31] arm64: Implement thread_struct whitelist for hardened usercopy

This whitelists the FPU register state portion of the thread_struct for
copying to userspace, instead of the default entire structure.

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: James Morse <james.morse@....com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: Dave Martin <Dave.Martin@....com>
Cc: zijun_hu <zijun_hu@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm64/Kconfig                 | 1 +
 arch/arm64/include/asm/processor.h | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0df64a6a56d4..e190f9901aef 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -73,6 +73,7 @@ config ARM64
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select HAVE_ARCH_VMAP_STACK
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 29adab8138c3..759c4d90ac7f 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -90,6 +90,14 @@ struct thread_struct {
 	struct debug_info	debug;		/* debugging */
 };
 
+/* Whitelist the fpsimd_state for copying to userspace. */
+static inline void arch_thread_struct_whitelist(unsigned long *offset,
+						unsigned long *size)
+{
+	*offset = offsetof(struct thread_struct, fpsimd_state);
+	*size = sizeof(struct fpsimd_state);
+}
+
 #ifdef CONFIG_COMPAT
 #define task_user_tls(t)						\
 ({									\
-- 
2.7.4