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

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Date: Mon, 15 Apr 2024 12:43:16 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Christoph Hellwig <hch@...radead.org>, Helge Deller <deller@....de>,
	Lorenzo Stoakes <lstoakes@...il.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Palmer Dabbelt <palmer@...belt.com>,
	Russell King <linux@...linux.org.uk>, Song Liu <song@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Uladzislau Rezki <urezki@...il.com>, Will Deacon <will@...nel.org>,
	bpf@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-modules@...r.kernel.org, linux-parisc@...r.kernel.org,
	linux-riscv@...ts.infradead.org, linux-trace-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [RFC PATCH 5/7] x86/module: perpare module loading for ROX
 allocations of text

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

>  
> -		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. 

>  		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).