[PATCH 4.4 49/53] retpoline: Introduce start/end markers of indirect thunk

Greg Kroah-Hartman
2018-01-22T08:40:41Z

From: Masami Hiramatsu <mhiramat@kernel.org>

commit 736e80a4213e9bbce40a7c050337047128b472ac upstream.

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>
Link: https://lkml.kernel.org/r/151629206178.10241.6828804696410044771.stgit@devbox
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/include/asm/nospec-branch.h | 3 +++
arch/x86/kernel/vmlinux.lds.S | 7 +++++++
arch/x86/lib/retpoline.S | 2 +-
3 files changed, 11 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -171,6 +171,9 @@ 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
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -104,6 +104,13 @@ SECTIONS
IRQENTRY_TEXT
*(.fixup)
*(.gnu.warning)
+
+#ifdef CONFIG_RETPOLINE
+ __indirect_thunk_start = .;
+ *(.text.__x86.indirect_thunk)
+ __indirect_thunk_end = .;
+#endif
+
/* End of text section */
_etext = .;
} :text = 0x9090
--- 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