Subject: Re: [RFC PATCH 5/7] x86/module: perpare module loading for ROX allocations of text

From: Mike Rapoport <[email-masked]>
Date: Mon, 15 Apr 2024 20:04:13 +0300

On Mon, Apr 15, 2024 at 12:43:16PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 11, 2024 at 07:05:24PM +0300, Mike Rapoport wrote:
> > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> > index 45a280f2161c..b4d6868df573 100644
> > --- a/arch/x86/kernel/alternative.c
> > +++ b/arch/x86/kernel/alternative.c
> 
> > @@ -504,17 +513,17 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
> >  		 *   patch if feature is *NOT* present.
> >  		 */
> >  		if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
> > -			optimize_nops_inplace(instr, a->instrlen);
> > +			optimize_nops_inplace(wr_instr, a->instrlen);
> >  			continue;
> >  		}
> >  
> > -		DPRINTK(ALT, "feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d) flags: 0x%x",
> > +		DPRINTK(ALT, "feat: %d*32+%d, old: (%px (%px) len: %d), repl: (%px (%px), len: %d) flags: 0x%x",
> >  			a->cpuid >> 5,
> >  			a->cpuid & 0x1f,
> > -			instr, instr, a->instrlen,
> > -			replacement, a->replacementlen, a->flags);
> > +			instr, wr_instr, a->instrlen,
> > +			replacement, wr_replacement, a->replacementlen, a->flags);
> 
> I think this, and

I've found printing both address handy when I debugged it, but no strong
feelings here.
 
> >  
> > -		memcpy(insn_buff, replacement, a->replacementlen);
> > +		memcpy(insn_buff, wr_replacement, a->replacementlen);
> >  		insn_buff_sz = a->replacementlen;
> >  
> >  		if (a->flags & ALT_FLAG_DIRECT_CALL) {
> > @@ -528,11 +537,11 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
> >  
> >  		apply_relocation(insn_buff, a->instrlen, instr, replacement, a->replacementlen);
> >  
> > -		DUMP_BYTES(ALT, instr, a->instrlen, "%px:   old_insn: ", instr);
> > +		DUMP_BYTES(ALT, wr_instr, a->instrlen, "%px:   old_insn: ", instr);
> 
> this, want to remain as is. 

here wr_instr is the buffer to dump:

DUMP_BYTES(type, buf, len, fmt, args...)

rather than an address, which remained 'instr'.
 
> >  		DUMP_BYTES(ALT, replacement, a->replacementlen, "%px:   rpl_insn: ", replacement);
> >  		DUMP_BYTES(ALT, insn_buff, insn_buff_sz, "%px: final_insn: ", instr);
> >  
> > -		text_poke_early(instr, insn_buff, insn_buff_sz);
> > +		text_poke_early(wr_instr, insn_buff, insn_buff_sz);
> >  	}
> >  
> >  	kasan_enable_current();
> 
> The rationale being that we then print an address that can be correlated
> to the kernel image (provided one either kills kaslr or adjusts for it).

-- 
Sincerely yours,
Mike.