linux-kernel - [PATCH 1/3] x86/alternative: Introduce int3_emulate

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Date:   Mon, 23 Jan 2023 21:59:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org
Cc:     tglx@...utronix.de, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, peterz@...radead.org,
        jpoimboe@...nel.org, jbaron@...mai.com, rostedt@...dmis.org,
        ardb@...nel.org, linux-kernel@...r.kernel.org,
        erhard_f@...lbox.org, ndesaulniers@...gle.com, mhiramat@...nel.org,
        sandipan.das@....com
Subject: [PATCH 1/3] x86/alternative: Introduce int3_emulate_jcc()

Move the kprobe Jcc emulation into int3_emulate_jcc() so it can be
used by more code -- specifically static_call() will need this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
 arch/x86/include/asm/text-patching.h |   31 ++++++++++++++++++++++++++++
 arch/x86/kernel/kprobes/core.c       |   38 +++++++----------------------------
 2 files changed, 39 insertions(+), 30 deletions(-)

--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -184,6 +184,37 @@ void int3_emulate_ret(struct pt_regs *re
 	unsigned long ip = int3_emulate_pop(regs);
 	int3_emulate_jmp(regs, ip);
 }
+
+static __always_inline
+void int3_emulate_jcc(struct pt_regs *regs, u8 cc, unsigned long ip, unsigned long disp)
+{
+	static const unsigned long jcc_mask[6] = {
+		[0] = X86_EFLAGS_OF,
+		[1] = X86_EFLAGS_CF,
+		[2] = X86_EFLAGS_ZF,
+		[3] = X86_EFLAGS_CF | X86_EFLAGS_ZF,
+		[4] = X86_EFLAGS_SF,
+		[5] = X86_EFLAGS_PF,
+	};
+
+	bool invert = cc & 1;
+	bool match;
+
+	if (cc < 0xc) {
+		match = regs->flags & jcc_mask[cc >> 1];
+	} else {
+		match = ((regs->flags & X86_EFLAGS_SF) >> X86_EFLAGS_SF_BIT) ^
+			((regs->flags & X86_EFLAGS_OF) >> X86_EFLAGS_OF_BIT);
+		if (cc >= 0xe)
+			match = match || (regs->flags & X86_EFLAGS_ZF);
+	}
+
+	if ((match && !invert) || (!match && invert))
+		ip += disp;
+
+	int3_emulate_jmp(regs, ip);
+}
+
 #endif /* !CONFIG_UML_X86 */
 
 #endif /* _ASM_X86_TEXT_PATCHING_H */
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -464,50 +464,26 @@ static void kprobe_emulate_call(struct k
 }
 NOKPROBE_SYMBOL(kprobe_emulate_call);
 
-static nokprobe_inline
-void __kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs, bool cond)
+static void kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs)
 {
 	unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
 
-	if (cond)
-		ip += p->ainsn.rel32;
+	ip += p->ainsn.rel32;
 	int3_emulate_jmp(regs, ip);
 }
-
-static void kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs)
-{
-	__kprobe_emulate_jmp(p, regs, true);
-}
 NOKPROBE_SYMBOL(kprobe_emulate_jmp);
 
-static const unsigned long jcc_mask[6] = {
-	[0] = X86_EFLAGS_OF,
-	[1] = X86_EFLAGS_CF,
-	[2] = X86_EFLAGS_ZF,
-	[3] = X86_EFLAGS_CF | X86_EFLAGS_ZF,
-	[4] = X86_EFLAGS_SF,
-	[5] = X86_EFLAGS_PF,
-};
-
 static void kprobe_emulate_jcc(struct kprobe *p, struct pt_regs *regs)
 {
-	bool invert = p->ainsn.jcc.type & 1;
-	bool match;
+	unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
 
-	if (p->ainsn.jcc.type < 0xc) {
-		match = regs->flags & jcc_mask[p->ainsn.jcc.type >> 1];
-	} else {
-		match = ((regs->flags & X86_EFLAGS_SF) >> X86_EFLAGS_SF_BIT) ^
-			((regs->flags & X86_EFLAGS_OF) >> X86_EFLAGS_OF_BIT);
-		if (p->ainsn.jcc.type >= 0xe)
-			match = match || (regs->flags & X86_EFLAGS_ZF);
-	}
-	__kprobe_emulate_jmp(p, regs, (match && !invert) || (!match && invert));
+	int3_emulate_jcc(regs, p->ainsn.jcc.type, ip, p->ainsn.rel32);
 }
 NOKPROBE_SYMBOL(kprobe_emulate_jcc);
 
 static void kprobe_emulate_loop(struct kprobe *p, struct pt_regs *regs)
 {
+	unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
 	bool match;
 
 	if (p->ainsn.loop.type != 3) {	/* LOOP* */
@@ -535,7 +511,9 @@ static void kprobe_emulate_loop(struct k
 	else if (p->ainsn.loop.type == 1)	/* LOOPE */
 		match = match && (regs->flags & X86_EFLAGS_ZF);
 
-	__kprobe_emulate_jmp(p, regs, match);
+	if (match)
+		ip += p->ainsn.rel32;
+	int3_emulate_jmp(regs, ip);
 }
 NOKPROBE_SYMBOL(kprobe_emulate_loop);