linux-kernel - Re: [PATCH v6 13/17] static_call: Add static_call

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Date:   Sat, 11 Jul 2020 12:49:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com,
        pbonzini@...hat.com, mathieu.desnoyers@...icios.com,
        linux@...musvillemoes.dk
Subject: Re: [PATCH v6 13/17] static_call: Add static_call_cond()

On Fri, Jul 10, 2020 at 07:08:25PM -0400, Steven Rostedt wrote:
> On Fri, 10 Jul 2020 15:38:44 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > +static void __static_call_transform(void *insn, enum insn_type type, void *func)
> >  {
> > -	const void *code = text_gen_insn(opcode, insn, func);
> > +	int size = CALL_INSN_SIZE;
> > +	const void *code;
> >  
> > -	if (WARN_ONCE(*(u8 *)insn != opcode,
> > -		      "unexpected static call insn opcode 0x%x at %pS\n",
> > -		      opcode, insn))
> 
> I would still feel better if we did some sort of sanity check before
> just writing to the text. Confirm this is a jmp, call, ret or nop?

Something like so (on top of the next patch) ?

I'm not convinced it actually helps much, but if it makes you feel
better :-)


--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -56,15 +56,36 @@ static inline enum insn_type __sc_insn(b
 	return 2*tail + null;
 }
 
+static void __static_call_validate(void *insn, bool tail)
+{
+	u8 opcode = *(u8 *)insn;
+
+	if (tail) {
+		if (opcode == JMP32_INSN_OPCODE ||
+		    opcode == RET_INSN_OPCODE)
+			return;
+	} else {
+		if (opcode == CALL_INSN_OPCODE ||
+		    !memcmp(insn, ideal_nops[NOP_ATOMIC5], 5))
+			return;
+	}
+
+	WARN_ONCE(1, "unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn);
+}
+
 void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
 {
 	mutex_lock(&text_mutex);
 
-	if (tramp)
+	if (tramp) {
+		__static_call_validate(tramp, true);
 		__static_call_transform(tramp, __sc_insn(!func, true), func);
+	}
 
-	if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site)
+	if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) {
+		__static_call_validate(site, tail);
 		__static_call_transform(site, __sc_insn(!func, tail), func);
+	}
 
 	mutex_unlock(&text_mutex);
 }