linux-kernel - Re: [PATCH v3] arch/x86: get rid of KERN_CONT in show_fault

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Date:   Tue, 26 Jun 2018 22:05:29 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Dmitry Vyukov <dvyukov@...il.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, sergey.senozhatsky.work@...il.com,
        andy.shevchenko@...il.com, Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v3] arch/x86: get rid of KERN_CONT in show_fault_oops()


* Dmitry Vyukov <dvyukov@...il.com> wrote:

> From: Dmitry Vyukov <dvyukov@...gle.com>
> 
> KERN_CONT leads to split lines in kernel output
> and complicates useful changes to printk like
> printing context before each line.
> 
> Only acceptable use of continuations is basically
> boot-time testing.
> 
> Get rid of it.
> 
> Also tidy up code around as asked by reviewers.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> 
> ---
> 
> Changes since v1:
>  - use pr_alert() instead of printk(KERN_ALERT)
> 
> Changes since v2:
>  - drop unnecessary parenthesis
>  - remove once used nx_warning and smep_warning
> ---
>  arch/x86/mm/fault.c | 21 +++++++--------------
>  1 file changed, 7 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 9a84a0d08727..a73575cacfd9 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -641,11 +641,6 @@ static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
>  	return 0;
>  }
>  
> -static const char nx_warning[] = KERN_CRIT
> -"kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n";
> -static const char smep_warning[] = KERN_CRIT
> -"unable to execute userspace code (SMEP?) (uid: %d)\n";
> -
>  static void
>  show_fault_oops(struct pt_regs *regs, unsigned long error_code,
>  		unsigned long address)
> @@ -664,20 +659,18 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code,
>  		pte = lookup_address_in_pgd(pgd, address, &level);
>  
>  		if (pte && pte_present(*pte) && !pte_exec(*pte))
> -			printk(nx_warning, from_kuid(&init_user_ns, current_uid()));
> +			pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n",
> +				from_kuid(&init_user_ns, current_uid()));
>  		if (pte && pte_present(*pte) && pte_exec(*pte) &&
>  				(pgd_flags(*pgd) & _PAGE_USER) &&
>  				(__read_cr4() & X86_CR4_SMEP))
> -			printk(smep_warning, from_kuid(&init_user_ns, current_uid()));
> +			pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n",
> +				from_kuid(&init_user_ns, current_uid()));
>  	}
>  
> -	printk(KERN_ALERT "BUG: unable to handle kernel ");
> -	if (address < PAGE_SIZE)
> -		printk(KERN_CONT "NULL pointer dereference");
> -	else
> -		printk(KERN_CONT "paging request");
> -
> -	printk(KERN_CONT " at %px\n", (void *) address);
> +	pr_alert("BUG: unable to handle kernel %s at %px\n",
> +		address < PAGE_SIZE ? "NULL pointer dereference" :
> +		"paging request", (void *) address);

I already applied the last hunk in a bit different way - could you send the rest 
as a separate clean-up patch please?

Thanks,

	Ingo