[PATCH -next] riscv: Implement thread_struct whitelist for hardened usercopy

[Tong Tiangen <tongtiangen@huawei.com>]

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

Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
---
 arch/riscv/Kconfig                 | 1 +
 arch/riscv/include/asm/processor.h | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 821081bdb8b8..5c26c0726944 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -70,6 +70,7 @@ config RISCV
 	select HAVE_ARCH_MMAP_RND_BITS if MMU
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
+	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_CONTEXT_TRACKING
 	select HAVE_DEBUG_KMEMLEAK
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 021ed64ee608..46b492c78cbb 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -37,6 +37,14 @@ struct thread_struct {
 	unsigned long bad_cause;
 };
 
+/* Whitelist the fstate from the task_struct for hardened usercopy */
+static inline void arch_thread_struct_whitelist(unsigned long *offset,
+						unsigned long *size)
+{
+	*offset = offsetof(struct thread_struct, fstate);
+	*size = sizeof_field(struct thread_struct, fstate);
+}
+
 #define INIT_THREAD {					\
 	.sp = sizeof(init_stack) + (long)&init_stack,	\
 }
-- 
2.25.1