[PATCH v2] powerpc: Implement arch_within_stack_frames

[Nicholas Miehlbradt]

Walks the stack when copy_{to,from}_user address is in the stack to
ensure that the object being copied is entirely within a single stack
frame.

Substatially similar to the x86 implementation except using the back
chain to traverse the stack and identify stack frame boundaries.

Signed-off-by: Nicholas Miehlbradt <nicholas at linux.ibm.com>
---
v2: Rename PARAMETER_SAVE_OFFSET to STACK_FRAME_PARAMS
    Add definitions of STACK_FRAME_PARAMS for PPC32 and remove dependancy on PPC64
    Ignore the current stack frame and start with it's parent, similar to x86

v1: https://lore.kernel.org/linuxppc-dev/20221214044252.1910657-1-nicholas@linux.ibm.com/
---
 arch/powerpc/Kconfig                   |  1 +
 arch/powerpc/include/asm/thread_info.h | 36 ++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2ca5418457ed..97ca54773521 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -198,6 +198,7 @@ config PPC
 	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
 	select HAVE_ARCH_KFENCE			if ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
+	select HAVE_ARCH_WITHIN_STACK_FRAMES
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index af58f1ed3952..c5dce5f239c1 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -186,6 +186,42 @@ static inline bool test_thread_local_flags(unsigned int flags)
 #define is_elf2_task() (0)
 #endif
 
+#if defined(CONFIG_PPC64_ELF_ABI_V1)
+#define STACK_FRAME_PARAMS 48
+#elif defined(CONFIG_PPC64_ELF_ABI_V2)
+#define STACK_FRAME_PARAMS 32
+#elif defined(CONFIG_PPC32)
+#define STACK_FRAME_PARAMS 8
+#endif
+
+/*
+ * Walks up the stack frames to make sure that the specified object is
+ * entirely contained by a single stack frame.
+ *
+ * Returns:
+ *	GOOD_FRAME	if within a frame
+ *	BAD_STACK	if placed across a frame boundary (or outside stack)
+ */
+static inline int arch_within_stack_frames(const void * const stack,
+					   const void * const stackend,
+					   const void *obj, unsigned long len)
+{
+	const void *params;
+	const void *frame;
+
+	params = *(const void * const *)current_stack_pointer + STACK_FRAME_PARAMS;
+	frame = **(const void * const * const *)current_stack_pointer;
+
+	while (stack <= frame && frame < stackend) {
+		if (obj + len <= frame)
+			return obj >= params ? GOOD_FRAME : BAD_STACK;
+		params = frame + STACK_FRAME_PARAMS;
+		frame = *(const void * const *)frame;
+	}
+
+	return BAD_STACK;
+}
+
 #endif	/* !__ASSEMBLY__ */
 
 #endif /* __KERNEL__ */
-- 
2.34.1