linux-kernel - Re: [PATCH v12 01/11] x86: text_poke() may access uninitialized struct pages

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Date:   Mon, 25 Jun 2018 10:14:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, john.stultz@...aro.org,
        sboyd@...eaurora.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        douly.fnst@...fujitsu.com, prarit@...hat.com, feng.tang@...el.com,
        pmladek@...e.com, gnomes@...rguk.ukuu.org.uk,
        linux-s390@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v12 01/11] x86: text_poke() may access uninitialized
 struct pages

On Thu, Jun 21, 2018 at 05:25:08PM -0400, Pavel Tatashin wrote:
> ---
>  arch/x86/include/asm/text-patching.h |  1 +
>  arch/x86/kernel/alternative.c        | 10 +++++++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
> index 2ecd34e2d46c..e85ff65c43c3 100644
> --- a/arch/x86/include/asm/text-patching.h
> +++ b/arch/x86/include/asm/text-patching.h
> @@ -37,5 +37,6 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len);
>  extern void *text_poke(void *addr, const void *opcode, size_t len);
>  extern int poke_int3_handler(struct pt_regs *regs);
>  extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
> +extern int after_bootmem;
>  
>  #endif /* _ASM_X86_TEXT_PATCHING_H */
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index a481763a3776..0230dbc3c599 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -686,13 +686,21 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode,
>   *
>   * Note: Must be called under text_mutex.
>   */
> -void *text_poke(void *addr, const void *opcode, size_t len)
> +void __ref *text_poke(void *addr, const void *opcode, size_t len)
>  {
>  	unsigned long flags;
>  	char *vaddr;
>  	struct page *pages[2];
>  	int i;
>  
> +	/* While boot memory allocator is runnig we cannot use struct

Broken comment style..

> +	 * pages as they are not yet initialized. However, we also know
> +	 * that this is early in boot, and it is safe to fallback to
> +	 * text_poke_early.
> +	 */
> +	if (unlikely(!after_bootmem))
> +		return text_poke_early(addr, opcode, len);

I'm not entirely sure this is right.. Because not only do we need the
whole fixmap stuff working, we also need #DB and the IPI handlers set-up
and working.

Also, why do this here and not override @poker in
__jump_label_transform() ?

And I added a sync_core() in text_poke_early(), which I think we need
for this.

>  	if (!core_kernel_text((unsigned long)addr)) {
>  		pages[0] = vmalloc_to_page(addr);
>  		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
> -- 
> 2.17.1
>