[29/36] x86: Implement thread_struct whitelist for hardened usercopy

Commit Message

Kees Cook Jan. 9, 2018, 8:55 p.m. UTC

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

Cc: Thomas Gleixner <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: [e-mail]
Cc: Borislav Petkov <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Mathias Krause <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>
Acked-by: Rik van Riel <[e-mail]>
---
 arch/x86/Kconfig                 | 1 +
 arch/x86/include/asm/processor.h | 8 ++++++++
 2 files changed, 9 insertions(+)

Patch

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8eed3f94bfc7..9ac4ac1a856b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -116,6 +116,7 @@  config X86
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if MMU && COMPAT
 	select HAVE_ARCH_COMPAT_MMAP_BASES	if MMU && COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index cc16fa882e3e..2b037b7fe0eb 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -492,6 +492,14 @@  struct thread_struct {
 	 */
 };
 
+/* Whitelist the FPU state 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, fpu.state);
+	*size = fpu_kernel_xstate_size;
+}
+
 /*
  * Thread-synchronous status.
  *