linux-kernel - [RFC PATCH 3/5] x86: interface for accessing indirect branch locations

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Message-ID: <20181018005420.82993-4-namit@vmware.com>
Date:   Wed, 17 Oct 2018 17:54:18 -0700
From:   Nadav Amit <namit@...are.com>
To:     Ingo Molnar <mingo@...hat.com>
CC:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "H . Peter Anvin " <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>, Nadav Amit <nadav.amit@...il.com>,
        <x86@...nel.org>, Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Nadav Amit <namit@...are.com>
Subject: [RFC PATCH 3/5] x86: interface for accessing indirect branch locations

Adding a C interface to access the locations of indirect branches. To be
used for dynamic patching.

Signed-off-by: Nadav Amit <namit@...are.com>
---
 arch/x86/include/asm/nospec-branch.h | 1 -
 arch/x86/include/asm/sections.h      | 2 ++
 include/linux/module.h               | 5 +++++
 kernel/module.c                      | 8 ++++++++
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index bd2d3a41e88c..a4496c141143 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -406,7 +406,6 @@ struct relpoline_entry {
 	u8 reg;
 } __packed;
 
-
 /* The Intel SPEC CTRL MSR base value cache */
 extern u64 x86_spec_ctrl_base;
 
diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index 8ea1cfdbeabc..e8dd9c40ecd5 100644
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -4,6 +4,7 @@
 
 #include <asm-generic/sections.h>
 #include <asm/extable.h>
+#include <asm/nospec-branch.h>
 
 extern char __brk_base[], __brk_limit[];
 extern struct exception_table_entry __stop___ex_table[];
@@ -11,6 +12,7 @@ extern char __end_rodata_aligned[];
 
 #if defined(CONFIG_X86_64)
 extern char __end_rodata_hpage_align[];
+extern const struct relpoline_entry __relpolines[], __relpolines_end[];
 #endif
 
 #endif	/* _ASM_X86_SECTIONS_H */
diff --git a/include/linux/module.h b/include/linux/module.h
index f807f15bebbe..29ff390f8339 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -39,6 +39,7 @@ struct modversion_info {
 
 struct module;
 struct exception_table_entry;
+struct relpoline_entry;
 
 struct module_kobject {
 	struct kobject kobj;
@@ -387,6 +388,10 @@ struct module {
 	unsigned int num_exentries;
 	struct exception_table_entry *extable;
 
+	/* Cachepolines */
+	unsigned int num_relpolines;
+	struct relpoline_entry *relpolines;
+
 	/* Startup function. */
 	int (*init)(void);
 
diff --git a/kernel/module.c b/kernel/module.c
index 49a405891587..e34fc28875bd 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -64,6 +64,7 @@
 #include <linux/bsearch.h>
 #include <linux/dynamic_debug.h>
 #include <linux/audit.h>
+#include <asm/nospec-branch.h>
 #include <uapi/linux/module.h>
 #include "module-internal.h"
 
@@ -256,6 +257,7 @@ static void mod_update_bounds(struct module *mod)
 #ifdef CONFIG_KGDB_KDB
 struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
 #endif /* CONFIG_KGDB_KDB */
+struct list_head *cachepoline_modules = &modules;
 
 static void module_assert_mutex(void)
 {
@@ -3125,6 +3127,12 @@ static int find_module_sections(struct module *mod, struct load_info *info)
 	mod->extable = section_objs(info, "__ex_table",
 				    sizeof(*mod->extable), &mod->num_exentries);
 
+#ifdef CONFIG_X86_64
+	mod->relpolines = section_objs(info, "__relpolines",
+					 sizeof(*mod->relpolines),
+					 &mod->num_relpolines);
+#endif
+
 	if (section_addr(info, "__obsparm"))
 		pr_warn("%s: Ignoring obsolete parameters\n", mod->name);
 
-- 
2.17.1