x86, vmlinux.lds: Add RUNTIME_DISCARD_EXIT to generic DISCARDS

In the x86 kernel, .exit.text and .exit.data sections are discarded at
runtime, not by the linker. Add RUNTIME_DISCARD_EXIT to generic DISCARDS
and define it in the x86 kernel linker script to keep them.

The sections are added before the DISCARD directive so document here
only the situation explicitly as this change doesn't have any effect on
the generated kernel. Also, other architectures like ARM64 will use it
too so generalize the approach with the RUNTIME_DISCARD_EXIT define.

 [ bp: Massage and extend commit message. ]

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200326193021.255002-1-hjl.tools@gmail.com

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index e3296aa028feb766ba79062d2acfe885becfd59b..7206e1ac23ddce7554589af025b7535c52947f51 100644 (file)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -21,6 +21,7 @@
 #define LOAD_OFFSET __START_KERNEL_map
 #endif
 
+#define RUNTIME_DISCARD_EXIT
 #define EMITS_PT_NOTE
 #define RO_EXCEPTION_TABLE_ALIGN       16
 

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e00f41aa8ec4f1ef955db01e7a9a8d0c1cfdec61..2444336ef04c5a2bf2baa33b92fccf37830ffa1a 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -894,10 +894,17 @@
  * section definitions so that such archs put those in earlier section
  * definitions.
  */
+#ifdef RUNTIME_DISCARD_EXIT
+#define EXIT_DISCARDS
+#else
+#define EXIT_DISCARDS                                                  \
+       EXIT_TEXT                                                       \
+       EXIT_DATA
+#endif
+
 #define DISCARDS                                                       \
        /DISCARD/ : {                                                   \
-       EXIT_TEXT                                                       \
-       EXIT_DATA                                                       \
+       EXIT_DISCARDS                                                   \
        EXIT_CALL                                                       \
        *(.discard)                                                     \
        *(.discard.*)                                                   \