Le 11/02/2022 à 01:56, Kees Cook a écrit :

On Thu, Feb 10, 2022 at 09:30:43PM +1100, Michael Ellerman wrote:

quoted

Christophe Leroy [off-list ref] writes:

quoted

diff --git a/kernel/extable.c b/kernel/extable.c
index b0ea5eb0c3b4..1ef13789bea9 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c

@@ -159,12 +160,32 @@ int kernel_text_address(unsigned long addr)
  }
  
  /*
- * On some architectures (PPC64, IA64) function pointers
+ * On some architectures (PPC64, IA64, PARISC) function pointers
   * are actually only tokens to some data that then holds the
   * real function address. As a result, to find if a function
   * pointer is part of the kernel text, we need to do some
   * special dereferencing first.
   */
+#ifdef CONFIG_HAVE_FUNCTION_DESCRIPTORS
+void *dereference_function_descriptor(void *ptr)
+{
+	func_desc_t *desc = ptr;
+	void *p;
+
+	if (!get_kernel_nofault(p, (void *)&desc->addr))
+		ptr = p;
+	return ptr;
+}

This needs an EXPORT_SYMBOL_GPL(), otherwise the build breaks after
patch 10 with CONFIG_LKDTM=m.

Oh good catch!

(There have been a few cases of LKDTM=m being the only thing needed a
symbol, so I've pondered giving it a namespace or constructing a little
ifdef wrapper... but this seems ok to export...)

powerpc and ia64 had it as a static inline, but parisc had it as a plain 
function and didn't export it. So I guess the export is not required at 
this point. I will export it in patch 10 when it becomes necessary.

Christophe