[PATCH v3] arch/x86: get rid of KERN_CONT in show_fault_oops()

[PATCH v3] arch/x86: get rid of KERN_CONT in show_fault_oops()

[Dmitry Vyukov]

From: Dmitry Vyukov <dvyukov@google.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@google.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.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);
 
 	dump_pagetable(address);
 }
-- 
2.18.0.rc2.346.g013aa6912e-goog

Re: [PATCH v3] arch/x86: get rid of KERN_CONT in show_fault_oops()

[Andy Shevchenko]

On Tue, Jun 26, 2018 at 10:28 AM, Dmitry Vyukov <dvyukov@gmail.com> wrote:
> From: Dmitry Vyukov <dvyukov@google.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.
>

FWIW,
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.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);
>
>         dump_pagetable(address);
>  }
> --
> 2.18.0.rc2.346.g013aa6912e-goog
>



-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3] arch/x86: get rid of KERN_CONT in show_fault_oops()

[Ingo Molnar]

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

> From: Dmitry Vyukov <dvyukov@google.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@google.com>
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.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

Re: [PATCH v3] arch/x86: get rid of KERN_CONT in show_fault_oops()

[Dmitry Vyukov]

On Tue, Jun 26, 2018 at 10:05 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Dmitry Vyukov <dvyukov@gmail.com> wrote:
>
>> From: Dmitry Vyukov <dvyukov@google.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@google.com>
>> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.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()".