arm64: implement function_nocfi

With CONFIG_CFI_CLANG, the compiler replaces function addresses in
instrumented C code with jump table addresses. This change implements
the function_nocfi() macro, which returns the actual function address
instead.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-13-samitolvanen@google.com

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 0aabc3b..3a6f9df 100644 (file)
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -321,6 +321,22 @@ static inline void *phys_to_virt(phys_addr_t x)
 #define virt_to_pfn(x)         __phys_to_pfn(__virt_to_phys((unsigned long)(x)))
 #define sym_to_pfn(x)          __phys_to_pfn(__pa_symbol(x))
 
+#ifdef CONFIG_CFI_CLANG
+/*
+ * With CONFIG_CFI_CLANG, the compiler replaces function address
+ * references with the address of the function's CFI jump table
+ * entry. The function_nocfi macro always returns the address of the
+ * actual function instead.
+ */
+#define function_nocfi(x) ({                                           \
+       void *addr;                                                     \
+       asm("adrp %0, " __stringify(x) "\n\t"                           \
+           "add  %0, %0, :lo12:" __stringify(x)                        \
+           : "=r" (addr));                                             \
+       addr;                                                           \
+})
+#endif
+
 /*
  *  virt_to_page(x)    convert a _valid_ virtual address to struct page *
  *  virt_addr_valid(x) indicates whether a virtual address is valid