linux-kernel - [PATCH v2 24/39] x86/text-patching: Make text_gen

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Message-ID: <20220224151323.421937384@infradead.org>
Date:   Thu, 24 Feb 2022 15:52:02 +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, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com
Subject: [PATCH v2 24/39] x86/text-patching: Make text_gen_insn() IBT aware

Make sure we don't generate direct JMP/CALL instructions to an ENDBR
instruction (which might be poison).

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/text-patching.h |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -5,6 +5,7 @@
 #include <linux/types.h>
 #include <linux/stddef.h>
 #include <asm/ptrace.h>
+#include <asm/ibt.h>
 
 struct paravirt_patch_site;
 #ifdef CONFIG_PARAVIRT
@@ -101,13 +102,26 @@ void *text_gen_insn(u8 opcode, const voi
 	static union text_poke_insn insn; /* per instance */
 	int size = text_opcode_size(opcode);
 
+	/*
+	 * Hide the addresses to avoid the compiler folding in constants when
+	 * referencing code, these can mess up annotations like
+	 * ANNOTATE_NOENDBR.
+	 */
+	OPTIMIZER_HIDE_VAR(addr);
+	OPTIMIZER_HIDE_VAR(dest);
+
+#ifdef CONFIG_X86_KERNEL_IBT
+	if (is_endbr(*(u32 *)dest))
+		dest += 4;
+#endif
+
 	insn.opcode = opcode;
 
 	if (size > 1) {
 		insn.disp = (long)dest - (long)(addr + size);
 		if (size == 2) {
 			/*
-			 * Ensure that for JMP9 the displacement
+			 * Ensure that for JMP8 the displacement
 			 * actually fits the signed byte.
 			 */
 			BUG_ON((insn.disp >> 31) != (insn.disp >> 7));