linux-kernel - [RFC][PATCH 6/6] x86/power: Seal restore_processor

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Date:   Thu, 12 Jan 2023 15:31:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, Joan Bruguera <joanbrugueram@...il.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        Juergen Gross <jgross@...e.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Jan Beulich <jbeulich@...e.com>,
        Roger Pau Monne <roger.pau@...rix.com>,
        Kees Cook <keescook@...omium.org>, mark.rutland@....com
Subject: [RFC][PATCH 6/6] x86/power: Seal restore_processor_state()

Disallow indirect branches to restore_processor_state().

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/suspend_64.h |    4 ++++
 arch/x86/power/cpu.c              |    2 +-
 arch/x86/power/hibernate_asm_64.S |    4 ++++
 include/linux/suspend.h           |    4 ++++
 4 files changed, 13 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/suspend_64.h
+++ b/arch/x86/include/asm/suspend_64.h
@@ -9,6 +9,7 @@
 
 #include <asm/desc.h>
 #include <asm/fpu/api.h>
+#include <asm/ibt.h>
 
 /*
  * Image of the saved processor state, used by the low level ACPI suspend to
@@ -61,4 +62,7 @@ struct saved_context {
 extern char core_restore_code[];
 extern char restore_registers[];
 
+#define restore_processor_state restore_processor_state
+extern __noendbr void restore_processor_state(void);
+
 #endif /* _ASM_X86_SUSPEND_64_H */
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -288,7 +288,7 @@ static __always_inline void __restore_pr
 }
 
 /* Needed by apm.c */
-void noinstr restore_processor_state(void)
+void __noendbr noinstr restore_processor_state(void)
 {
 	__restore_processor_state(&saved_context);
 }
--- a/arch/x86/power/hibernate_asm_64.S
+++ b/arch/x86/power/hibernate_asm_64.S
@@ -23,6 +23,10 @@
 #include <asm/frame.h>
 #include <asm/nospec-branch.h>
 
+.pushsection .discard.noendbr
+.quad	restore_processor_state
+.popsection
+
 	 /* code below belongs to the image kernel */
 	.align PAGE_SIZE
 SYM_FUNC_START(restore_registers)
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -9,6 +9,7 @@
 #include <linux/mm.h>
 #include <linux/freezer.h>
 #include <asm/errno.h>
+#include <asm/suspend.h>
 
 #ifdef CONFIG_VT
 extern void pm_set_vt_switch(int);
@@ -483,7 +484,10 @@ extern struct mutex system_transition_mu
 
 #ifdef CONFIG_PM_SLEEP
 void save_processor_state(void);
+
+#ifndef restore_processor_state
 void restore_processor_state(void);
+#endif
 
 /* kernel/power/main.c */
 extern int register_pm_notifier(struct notifier_block *nb);