linux-kernel - [PATCH 04/29] x86/livepatch: Validate __fentry_

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Date:   Fri, 18 Feb 2022 17:49:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, Miroslav Benes <mbenes@...e.cz>
Subject: [PATCH 04/29] x86/livepatch: Validate __fentry__ location

Currently livepatch assumes __fentry__ lives at func+0, which is most
likely untrue with IBT on. Override the weak klp_get_ftrace_location()
function with an arch specific version that's IBT aware.

Also make the weak fallback verify the location is an actual ftrace
location as a sanity check.

Suggested-by: Miroslav Benes <mbenes@...e.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/livepatch.h |    9 +++++++++
 kernel/livepatch/patch.c         |    2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/livepatch.h
+++ b/arch/x86/include/asm/livepatch.h
@@ -17,4 +17,13 @@ static inline void klp_arch_set_pc(struc
 	ftrace_instruction_pointer_set(fregs, ip);
 }
 
+#define klp_get_ftrace_location klp_get_ftrace_location
+static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
+{
+	unsigned long addr = ftrace_location(faddr);
+	if (!addr && IS_ENABLED(CONFIG_X86_IBT))
+		addr = ftrace_location(faddr + 4);
+	return addr;
+}
+
 #endif /* _ASM_X86_LIVEPATCH_H */
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -133,7 +133,7 @@ static void notrace klp_ftrace_handler(u
 #ifndef klp_get_ftrace_location
 static unsigned long klp_get_ftrace_location(unsigned long faddr)
 {
-	return faddr;
+	return ftrace_location(faddr);
 }
 #endif