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SubjectRe: [PATCH] mm: kmemleak: check boundary of objects allocated with physical address when scan
On Tue, May 31, 2022 at 11:08:23PM +0800, Patrick Wang wrote:
> @@ -1132,8 +1135,13 @@ EXPORT_SYMBOL(kmemleak_no_scan);
> void __ref kmemleak_alloc_phys(phys_addr_t phys, size_t size, int min_count,
> gfp_t gfp)
> {
> - if (PHYS_PFN(phys) >= min_low_pfn && PHYS_PFN(phys) < max_low_pfn)
> - kmemleak_alloc(__va(phys), size, min_count, gfp);
> + pr_debug("%s(0x%p, %zu, %d)\n", __func__, __va(phys), size, min_count);

I'd print just phys here since that's the function argument.

> + if (kmemleak_enabled && (unsigned long)__va(phys) >= PAGE_OFFSET &&
> + !IS_ERR(__va(phys)))
> + /* create object with OBJECT_PHYS flag */
> + create_object((unsigned long)__va(phys), size, min_count,
> + gfp, true);

Do we still need to check for __va(phys) >= PAGE_OFFSET? Also I don't
think IS_ERR(__va(phys)) makes sense, we can't store an error in a
physical address. The kmemleak_alloc_phys() function is only called on
successful allocation, so shouldn't bother with error codes.

> @@ -1436,6 +1441,13 @@ static void kmemleak_scan(void)
> dump_object_info(object);
> }
> #endif
> +
> + /* outside lowmem, make it black */

Maybe a bit more verbose:

/* ignore objects outside lowmem (paint them black) */

> + if (object->flags & OBJECT_PHYS)
> + if (PHYS_PFN(__pa((void *)object->pointer)) < min_low_pfn ||
> + PHYS_PFN(__pa((void *)object->pointer)) >= max_low_pfn)
> + __paint_it(object, KMEMLEAK_BLACK);

I'd skip the checks if the object is OBJECT_NO_SCAN (side-effect of
__paint_it()) so that the next scan won't have to go through the __pa()
checks again. It's also probably more correct to check the upper object
boundary). Something like:

if ((object->flags & OBJECT_PHYS) &&
!(object->flags & OBJECT_NO_SCAN)) {
unsigned long phys = __pa((void *)object->pointer);
if (PHYS_PFN(phys) < min_low_pfn ||
PHYS_PFN(phys + object->size) >= max_low_pfn)
__paint_it(object, KMEMLEAK_BLACK);
}

Thanks.

--
Catalin

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