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Subject[tip:x86/pti] retpoline: Introduce start/end markers of indirect thunk
Commit-ID:  736e80a4213e9bbce40a7c050337047128b472ac
Gitweb: https://git.kernel.org/tip/736e80a4213e9bbce40a7c050337047128b472ac
Author: Masami Hiramatsu <mhiramat@kernel.org>
AuthorDate: Fri, 19 Jan 2018 01:14:21 +0900
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 19 Jan 2018 16:31:28 +0100

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

---
arch/x86/include/asm/nospec-branch.h | 3 +++
arch/x86/kernel/vmlinux.lds.S | 6 ++++++
arch/x86/lib/retpoline.S | 2 +-
3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 7b45d84..19ba5ad 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 1e413a93..9b138a0 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 cb45c6c..d3415dc 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
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