linux-kernel - [PATCH v1 tip/master 1/3] retpoline: Introduce start/end markers of indirect thunk

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Date:   Thu, 18 Jan 2018 21:01:19 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>, David Woodhouse <dwmw@...zon.co.uk>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>
Subject: [PATCH v1 tip/master 1/3] retpoline: Introduce start/end markers of indirect thunk

Introduce start/end markers of __x86_indirect_thunk_* functions.
These thunk functions are placed in .text.__x86.indirect_thunk.*
sections. So this puts those sections in the end of kernel text
and adds __indirect_thunk_start/end so that other subsystem
(e.g. kprobes) can identify it.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 arch/x86/include/asm/nospec-branch.h |    3 +++
 arch/x86/kernel/vmlinux.lds.S        |   35 ++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

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..1a5a663620ce 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -74,6 +74,9 @@ jiffies_64 = jiffies;
 
 #endif
 
+#define X86_INDIRECT_THUNK(reg)	\
+		*(.text.__x86.indirect_thunk.##reg)
+
 PHDRS {
 	text PT_LOAD FLAGS(5);          /* R_E */
 	data PT_LOAD FLAGS(6);          /* RW_ */
@@ -124,6 +127,38 @@ SECTIONS
 		ASSERT(. - _entry_trampoline == PAGE_SIZE, "entry trampoline is too big");
 #endif
 
+#ifdef CONFIG_RETPOLINE
+		__indirect_thunk_start = .;
+#ifdef CONFIG_X86_64
+		X86_INDIRECT_THUNK(rax)
+		X86_INDIRECT_THUNK(rbx)
+		X86_INDIRECT_THUNK(rcx)
+		X86_INDIRECT_THUNK(rdx)
+		X86_INDIRECT_THUNK(rsi)
+		X86_INDIRECT_THUNK(rdi)
+		X86_INDIRECT_THUNK(rbp)
+		X86_INDIRECT_THUNK(rsp)
+		X86_INDIRECT_THUNK(r8)
+		X86_INDIRECT_THUNK(r9)
+		X86_INDIRECT_THUNK(r10)
+		X86_INDIRECT_THUNK(r11)
+		X86_INDIRECT_THUNK(r12)
+		X86_INDIRECT_THUNK(r13)
+		X86_INDIRECT_THUNK(r14)
+		X86_INDIRECT_THUNK(r15)
+#else
+		X86_INDIRECT_THUNK(eax)
+		X86_INDIRECT_THUNK(ebx)
+		X86_INDIRECT_THUNK(ecx)
+		X86_INDIRECT_THUNK(edx)
+		X86_INDIRECT_THUNK(esi)
+		X86_INDIRECT_THUNK(edi)
+		X86_INDIRECT_THUNK(ebp)
+		X86_INDIRECT_THUNK(esp)
+#endif
+		__indirect_thunk_end = .;
+#endif
+
 		/* End of text section */
 		_etext = .;
 	} :text = 0x9090