'array_ptr' uses a mask to sanitize user controllable pointers. The x86
'array_ptr_mask' is an assembler optimized way to generate a 0 or ~0
mask if an array index is out-of-bounds or in-bounds.
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
arch/x86/include/asm/barrier.h | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
index 01727dbc294a..e8fd92008eab 100644
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h
@@ -24,6 +24,30 @@
#define wmb() asm volatile("sfence" ::: "memory")
#endif
+/**
+ * array_ptr_mask - generate a mask for array_ptr() that is ~0UL when
+ * the bounds check succeeds and 0 otherwise
+ */
+#define array_ptr_mask array_ptr_mask
+static inline unsigned long array_ptr_mask(unsigned long idx, unsigned long sz)
+{
+ unsigned long mask;
+
+ /*
+ * mask = index - size, if that result is >= 0 then the index is
+ * invalid and the mask is 0 else ~0
+ */
+#ifdef CONFIG_X86_32
+ asm ("cmpl %1,%2; sbbl %0,%0;"
+#else
+ asm ("cmpq %1,%2; sbbq %0,%0;"
+#endif
+ :"=r" (mask)
+ :"r"(sz),"r" (idx)
+ :"cc");
+ return mask;
+}
+
#ifdef CONFIG_X86_PPRO_FENCE
#define dma_rmb() rmb()
#else
