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

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Date:   Wed, 27 Jun 2018 11:07:41 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Dmitry Vyukov <dvyukov@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v3] arch/x86: get rid of KERN_CONT in show_fault_oops()

On Tue, Jun 26, 2018 at 10:05 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * 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?

Just mailed "arch/x86: cleanup show_fault_oops()".