arm64: Implement thread_struct whitelist for hardened usercopy

While ARM64 carries FPU state in the thread structure that is saved and
restored during signal handling, it doesn't need to declare a usercopy
whitelist, since existing accessors are all either using a bounce buffer
(for which whitelisting isn't checking the slab), are statically sized
(which will bypass the hardened usercopy check), or both.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: zijun_hu <zijun_hu@htc.com>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a93339f..c84477e 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -90,6 +90,7 @@ 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 023cacb..ba6c9ce 100644 (file)
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -113,6 +113,16 @@ struct thread_struct {
        struct debug_info       debug;          /* debugging */
 };
 
+/*
+ * Everything usercopied to/from thread_struct is statically-sized, so
+ * no hardened usercopy whitelist is needed.
+ */
+static inline void arch_thread_struct_whitelist(unsigned long *offset,
+                                               unsigned long *size)
+{
+       *offset = *size = 0;
+}
+
 #ifdef CONFIG_COMPAT
 #define task_user_tls(t)                                               \
 ({                                                                     \