[PATCH 33/38] 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@arm.com>
Cc: Will Deacon <redacted>
Cc: Christian Borntraeger <redacted>
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 <redacted>
Cc: linux-arm-kernel at lists.infradead.org
Signed-off-by: Kees Cook <redacted>
---
 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 a93339f5178f..c84477e6a884 100644
--- 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 023cacb946c3..e58a5864ec89 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h

@@ -113,6 +113,14 @@ 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);