Re: [PATCH v9 19/21] mm: Add generic ptdump

[Mark Rutland]

On Mon, Jul 22, 2019 at 04:42:08PM +0100, Steven Price wrote:
> Add a generic version of page table dumping that architectures can
> opt-in to
> 
> Signed-off-by: Steven Price <steven.price@xxxxxxx>

[...]

> +#ifdef CONFIG_KASAN
> +/*
> + * This is an optimization for KASAN=y case. Since all kasan page tables
> + * eventually point to the kasan_early_shadow_page we could call note_page()
> + * right away without walking through lower level page tables. This saves
> + * us dozens of seconds (minutes for 5-level config) while checking for
> + * W+X mapping or reading kernel_page_tables debugfs file.
> + */
> +static inline bool kasan_page_table(struct ptdump_state *st, void *pt,
> +				    unsigned long addr)
> +{
> +	if (__pa(pt) == __pa(kasan_early_shadow_pmd) ||
> +#ifdef CONFIG_X86
> +	    (pgtable_l5_enabled() &&
> +			__pa(pt) == __pa(kasan_early_shadow_p4d)) ||
> +#endif
> +	    __pa(pt) == __pa(kasan_early_shadow_pud)) {
> +		st->note_page(st, addr, 5, pte_val(kasan_early_shadow_pte[0]));
> +		return true;
> +	}
> +	return false;

Having you tried this with CONFIG_DEBUG_VIRTUAL?

The kasan_early_shadow_pmd is a kernel object rather than a linear map
object, so you should use __pa_symbol for that.

It's a bit horrid to have to test multiple levels in one function; can't
we check the relevant level inline in each of the test_p?d funcs?

They're optional anyway, so they only need to be defined for
CONFIG_KASAN.

Thanks,
Mark.

> +}
> +#else
> +static inline bool kasan_page_table(struct ptdump_state *st, void *pt,
> +				    unsigned long addr)
> +{
> +	return false;
> +}
> +#endif
> +
> +static int ptdump_test_p4d(unsigned long addr, unsigned long next,
> +			   p4d_t *p4d, struct mm_walk *walk)
> +{
> +	struct ptdump_state *st = walk->private;
> +
> +	if (kasan_page_table(st, p4d, addr))
> +		return 1;
> +	return 0;
> +}
> +static int ptdump_test_pud(unsigned long addr, unsigned long next,
> +			   pud_t *pud, struct mm_walk *walk)
> +{
> +	struct ptdump_state *st = walk->private;
> +
> +	if (kasan_page_table(st, pud, addr))
> +		return 1;
> +	return 0;
> +}
> +
> +static int ptdump_test_pmd(unsigned long addr, unsigned long next,
> +			   pmd_t *pmd, struct mm_walk *walk)
> +{
> +	struct ptdump_state *st = walk->private;
> +
> +	if (kasan_page_table(st, pmd, addr))
> +		return 1;
> +	return 0;
> +}
> +
> +static int ptdump_hole(unsigned long addr, unsigned long next,
> +		       struct mm_walk *walk)
> +{
> +	struct ptdump_state *st = walk->private;
> +
> +	st->note_page(st, addr, -1, 0);
> +
> +	return 0;
> +}
> +
> +void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)
> +{
> +	struct mm_walk walk = {
> +		.mm		= mm,
> +		.pgd_entry	= ptdump_pgd_entry,
> +		.p4d_entry	= ptdump_p4d_entry,
> +		.pud_entry	= ptdump_pud_entry,
> +		.pmd_entry	= ptdump_pmd_entry,
> +		.pte_entry	= ptdump_pte_entry,
> +		.test_p4d	= ptdump_test_p4d,
> +		.test_pud	= ptdump_test_pud,
> +		.test_pmd	= ptdump_test_pmd,
> +		.pte_hole	= ptdump_hole,
> +		.private	= st
> +	};
> +	const struct ptdump_range *range = st->range;
> +
> +	down_read(&mm->mmap_sem);
> +	while (range->start != range->end) {
> +		walk_page_range(range->start, range->end, &walk);
> +		range++;
> +	}
> +	up_read(&mm->mmap_sem);
> +
> +	/* Flush out the last page */
> +	st->note_page(st, 0, 0, 0);
> +}
> -- 
> 2.20.1
>