Walks the stack when copy_{to,from}_user address is in the stack to
ensure that the object being copied is entirely a single stack frame and
does not contain stack metadata.
Substantially similar to the x86 implementation. The back chain is used
to traverse the stack and identify stack frame boundaries.
Signed-off-by: Nicholas Miehlbradt <nicho...@linux.ibm.com>
---
v3: Move STACK_FRAME_PARAMS macros to ppc_asm.h
Add diagram in comments to show position of pointers into the stack during
execution
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-nicho...@linux.ibm.com/
v2:
https://lore.kernel.org/linuxppc-dev/20230119053127.17782-1-nicho...@linux.ibm.com/
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/ppc_asm.h | 8 ++++++
arch/powerpc/include/asm/thread_info.h | 38 ++++++++++++++++++++++++++
3 files changed, 47 insertions(+)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2c9cdf1d8761..3ce17f9aa90a 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -200,6 +200,7 @@ config PPC
select HAVE_ARCH_KCSAN if PPC_BOOK3S_64
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/ppc_asm.h
b/arch/powerpc/include/asm/ppc_asm.h
index d2f44612f4b0..1f1a64b780e3 100644
--- a/arch/powerpc/include/asm/ppc_asm.h
+++ b/arch/powerpc/include/asm/ppc_asm.h
@@ -837,4 +837,12 @@ END_FTR_SECTION_NESTED(CPU_FTR_CELL_TB_BUG,
CPU_FTR_CELL_TB_BUG, 96)
#define BTB_FLUSH(reg)
#endif /* CONFIG_PPC_E500 */
+#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
+
#endif /* _ASM_POWERPC_PPC_ASM_H */
diff --git a/arch/powerpc/include/asm/thread_info.h
b/arch/powerpc/include/asm/thread_info.h
index af58f1ed3952..07f1901da8fd 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -45,6 +45,7 @@
#include <linux/cache.h>
#include <asm/processor.h>
#include <asm/accounting.h>
+#include <asm/ppc_asm.h>
#define SLB_PRELOAD_NR 16U
/*
@@ -186,6 +187,43 @@ static inline bool test_thread_local_flags(unsigned int
flags)
#define is_elf2_task() (0)
#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;
+
+ /*
+ * low -----------------------------------------------------------> high
+ * [backchain][metadata][params][local vars][saved registers][backchain]
+ * ^------------------------------------^
+ * | allows copies only in this region |
+ * | |
+ * params frame
+ * The metadata region contains the saved LR, CR etc.
+ */
+ 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
