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

From: Ingo Molnar
Date: Tue Jun 26 2018 - 16:05:38 EST



* Dmitry Vyukov <dvyukov@xxxxxxxxx> wrote:

> From: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
>
> ---
>
> 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