x86, vmlinux.lds: Add RUNTIME_DISCARD_EXIT to generic DISCARDS

commit aab2867d7f88f537bbaa9e59551377918631abeb upstream.

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
Signed-off-by: Tom Saeger <tom.saeger@oracle.com>

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 1afe211d7a7ca279f407eebae5886d0569068710..7e0e21082c93e861a51165dbc93849c55911503f 100644 (file)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -21,6 +21,8 @@
 #define LOAD_OFFSET __START_KERNEL_map
 #endif
 
+#define RUNTIME_DISCARD_EXIT
+
 #include <asm-generic/vmlinux.lds.h>
 #include <asm/asm-offsets.h>
 #include <asm/thread_info.h>

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index c3bcac22c3894d29c675d23f091fb4cae9d66ab8..2d45d98773e232134dd94099eabce1574b4806f5 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -900,10 +900,17 @@
  * 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.*)                                                   \