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SubjectRe: [PATCH v2] powerpc/mm: make NULL pointer deferences explicit on bad page faults.
Date
Christophe Leroy <christophe.leroy@c-s.fr> writes:

> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 01b9bcc7fa85..3398291f4785 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -636,21 +636,24 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
> switch (TRAP(regs)) {
> case 0x300:
> case 0x380:
> - printk(KERN_ALERT "Unable to handle kernel paging request for "
> - "data at address 0x%08lx\n", regs->dar);
> + if (regs->dar < PAGE_SIZE)
> + pr_alert("BUG: Kernel NULL pointer dereference");
> + else
> + pr_alert("BUG: Unable to handle kernel data access");
> + pr_cont(" at 0x%08lx\n", regs->dar);

It's best to avoid pr_cont() as it can lead to interleaving, so I
rewrote this as:

pr_alert("BUG: %s at 0x%08lx\n",
regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
"Unable to handle kernel data access", regs->dar);


> break;
> case 0x400:
> case 0x480:
> - printk(KERN_ALERT "Unable to handle kernel paging request for "
> - "instruction fetch\n");
> + pr_alert("BUG: Unable to handle kernel instruction fetch%s",
> + regs->nip < PAGE_SIZE ? " (NULL pointer ?)\n" : "\n");
I dropped the space here ^


cheers

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