[PATCH v2 01/11] mm: Implement stack frame object validation

Kees Cook
2016-07-13T21:56:25Z

This creates per-architecture function arch_within_stack_frames() that
should validate if a given object is contained by a kernel stack frame.
Initial implementation is on x86.

This is based on code from PaX.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/Kconfig | 9 ++++++++
arch/x86/Kconfig | 1 +
arch/x86/include/asm/thread_info.h | 44 ++++++++++++++++++++++++++++++++++++++
include/linux/thread_info.h | 9 ++++++++
4 files changed, 63 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index d794384a0404..5e2776562035 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -424,6 +424,15 @@ config CC_STACKPROTECTOR_STRONG

endchoice

+config HAVE_ARCH_WITHIN_STACK_FRAMES
+ bool
+ help
+ An architecture should select this if it can walk the kernel stack
+ frames to determine if an object is part of either the arguments
+ or local variables (i.e. that it excludes saved return addresses,
+ and similar) by implementing an inline arch_within_stack_frames(),
+ which is used by CONFIG_HARDENED_USERCOPY.
+
config HAVE_CONTEXT_TRACKING
bool
help
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0a7b885964ba..4407f596b72c 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -91,6 +91,7 @@ config X86
select HAVE_ARCH_SOFT_DIRTY if X86_64
select HAVE_ARCH_TRACEHOOK
select HAVE_ARCH_TRANSPARENT_HUGEPAGE
+ select HAVE_ARCH_WITHIN_STACK_FRAMES
select HAVE_EBPF_JIT if X86_64
select HAVE_CC_STACKPROTECTOR
select HAVE_CMPXCHG_DOUBLE
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 30c133ac05cd..ab386f1336f2 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -180,6 +180,50 @@ static inline unsigned long current_stack_pointer(void)
return sp;
}

+/*
+ * Walks up the stack frames to make sure that the specified object is
+ * entirely contained by a single stack frame.
+ *
+ * Returns:
+ * 1 if within a frame
+ * -1 if placed across a frame boundary (or outside stack)
+ * 0 unable to determine (no frame pointers, etc)
+ */
+static inline int arch_within_stack_frames(const void * const stack,
+ const void * const stackend,
+ const void *obj, unsigned long len)
+{
+#if defined(CONFIG_FRAME_POINTER)
+ const void *frame = NULL;
+ const void *oldframe;
+
+ oldframe = __builtin_frame_address(1);
+ if (oldframe)
+ frame = __builtin_frame_address(2);
+ /*
+ * low ----------------------------------------------> high
+ * [saved bp][saved ip][args][local vars][saved bp][saved ip]
+ * ^----------------^
+ * allow copies only within here
+ */
+ while (stack <= frame && frame < stackend) {
+ /*
+ * If obj + len extends past the last frame, this
+ * check won't pass and the next frame will be 0,
+ * causing us to bail out and correctly report
+ * the copy as invalid.
+ */
+ if (obj + len <= frame)
+ return obj >= oldframe + 2 * sizeof(void *) ? 1 : -1;
+ oldframe = frame;
+ frame = *(const void * const *)frame;
+ }
+ return -1;
+#else
+ return 0;
+#endif
+}
+
#else /* !__ASSEMBLY__ */

#ifdef CONFIG_X86_64
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index b4c2a485b28a..3d5c80b4391d 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -146,6 +146,15 @@ static inline bool test_and_clear_restore_sigmask(void)
#error "no set_restore_sigmask() provided and default one won't work"
#endif

+#ifndef CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES
+static inline int arch_within_stack_frames(const void * const stack,
+ const void * const stackend,
+ const void *obj, unsigned long len)
+{
+ return 0;
+}
+#endif
+
#endif /* __KERNEL__ */

#endif /* _LINUX_THREAD_INFO_H */
--
2.7.4