retpoline: Introduce start/end markers of indirect thunk

Introduce start/end markers of __x86_indirect_thunk_* functions.
To make it easy, consolidate .text.__x86.indirect_thunk.* sections
to one .text.__x86.indirect_thunk section and put it in the
end of kernel text section and adds __indirect_thunk_start/end
so that other subsystem (e.g. kprobes) can identify it.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/151629206178.10241.6828804696410044771.stgit@devbox

3 files changed, 10 insertions, 1 deletions

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 7b45d8424150..19ba5ad19c65 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -194,6 +194,9 @@ enum spectre_v2_mitigation {
         SPECTRE_V2_IBRS,
 };
 
+extern char __indirect_thunk_start[];
+extern char __indirect_thunk_end[];
+
 /*
  * On VMEXIT we must ensure that no RSB predictions learned in the guest
  * can be followed in the host, by overwriting the RSB completely. Both
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 1e413a9326aa..9b138a06c1a4 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -124,6 +124,12 @@ SECTIONS
                 ASSERT(. - _entry_trampoline == PAGE_SIZE, "entry trampoline is too big");
 #endif
 
+#ifdef CONFIG_RETPOLINE
+                __indirect_thunk_start = .;
+                *(.text.__x86.indirect_thunk)
+                __indirect_thunk_end = .;
+#endif
+
                 /* End of text section */
                 _etext = .;
         } :text = 0x9090
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index cb45c6cb465f..d3415dc30f82 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -9,7 +9,7 @@
 #include <asm/nospec-branch.h>
 
 .macro THUNK reg
-        .section .text.__x86.indirect_thunk.\reg
+        .section .text.__x86.indirect_thunk
 
 ENTRY(__x86_indirect_thunk_\reg)
         CFI_STARTPROC