Re: [PATCH 3/3] kasan: fix zeroing vmalloc memory with HW_TAGS
From: Marco Elver
Date: Wed Jun 01 2022 - 08:29:06 EST
On Tue, May 31, 2022 at 05:43PM +0200, andrey.konovalov@xxxxxxxxx wrote:
> From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>
> HW_TAGS KASAN skips zeroing page_alloc allocations backing vmalloc
> mappings via __GFP_SKIP_ZERO. Instead, these pages are zeroed via
> kasan_unpoison_vmalloc() by passing the KASAN_VMALLOC_INIT flag.
>
> The problem is that __kasan_unpoison_vmalloc() does not zero pages
> when either kasan_vmalloc_enabled() or is_vmalloc_or_module_addr() fail.
>
> Thus:
>
> 1. Change __vmalloc_node_range() to only set KASAN_VMALLOC_INIT when
> __GFP_SKIP_ZERO is set.
>
> 2. Change __kasan_unpoison_vmalloc() to always zero pages when the
> KASAN_VMALLOC_INIT flag is set.
>
> 3. Add WARN_ON() asserts to check that KASAN_VMALLOC_INIT cannot be set
> in other early return paths of __kasan_unpoison_vmalloc().
>
> Also clean up the comment in __kasan_unpoison_vmalloc.
>
> Fixes: 23689e91fb22 ("kasan, vmalloc: add vmalloc tagging for HW_TAGS")
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
> mm/kasan/hw_tags.c | 30 ++++++++++++++++++++++--------
> mm/vmalloc.c | 10 +++++-----
> 2 files changed, 27 insertions(+), 13 deletions(-)
>
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 9e1b6544bfa8..c0ec01eadf20 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -263,21 +263,31 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> u8 tag;
> unsigned long redzone_start, redzone_size;
>
> - if (!kasan_vmalloc_enabled())
> - return (void *)start;
> + if (!kasan_vmalloc_enabled() || !is_vmalloc_or_module_addr(start)) {
> + struct page *page;
> + const void *addr;
> +
> + /* Initialize memory if required. */
> +
This whole block of code looks out-of-place in this function, since it's
not at all related to unpoisoning but a fallback if KASAN-vmalloc is off
but we still want to initialize the memory.
Maybe to ease readability here I'd change it to look like:
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 11f661a2494b..227c20d09258 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -257,6 +257,21 @@ static void unpoison_vmalloc_pages(const void *addr, u8 tag)
}
}
+/*
+ * Explicit initialization of pages if KASAN does not handle VM_ALLOC
+ * allocations.
+ */
+static void init_vmalloc_pages_explicit(const void *start, unsigned long size)
+{
+ const void *addr;
+
+ for (addr = start; addr < start + size; addr += PAGE_SIZE) {
+ struct page *page = virt_to_page(addr);
+
+ clear_highpage_kasan_tagged(page);
+ }
+}
+
void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
kasan_vmalloc_flags_t flags)
{
@@ -264,19 +279,8 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
unsigned long redzone_start, redzone_size;
if (!kasan_vmalloc_enabled() || !is_vmalloc_or_module_addr(start)) {
- struct page *page;
- const void *addr;
-
- /* Initialize memory if required. */
-
- if (!(flags & KASAN_VMALLOC_INIT))
- return (void *)start;
-
- for (addr = start; addr < start + size; addr += PAGE_SIZE) {
- page = virt_to_page(addr);
- clear_highpage_kasan_tagged(page);
- }
-
+ if (flags & KASAN_VMALLOC_INIT)
+ init_vmalloc_pages_explicit(start, size);
return (void *)start;
}