linux-kernel - Re: [PATCH] kasan: fix unaligned address is unhandled in kasan_remove_zero

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Date:   Fri, 8 Jan 2021 19:25:42 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mediatek@...ts.infradead.org, yj.chiang@...iatek.com,
        Lecopzer Chen <lecopzer@...il.com>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>
Subject: Re: [PATCH] kasan: fix unaligned address is unhandled in kasan_remove_zero_shadow

On Sun, Jan 3, 2021 at 2:56 PM Lecopzer Chen <lecopzer@...il.com> wrote:
>
> During testing kasan_populate_early_shadow and kasan_remove_zero_shadow,
> if the shadow start and end address in kasan_remove_zero_shadow() is
> not aligned to PMD_SIZE, the remain unaligned PTE won't be removed.
>
> In the test case for kasan_remove_zero_shadow():
>     shadow_start: 0xffffffb802000000, shadow end: 0xffffffbfbe000000
>     3-level page table:
>       PUD_SIZE: 0x40000000 PMD_SIZE: 0x200000 PAGE_SIZE: 4K
> 0xffffffbf80000000 ~ 0xffffffbfbdf80000 will not be removed because
> in kasan_remove_pud_table(), kasan_pmd_table(*pud) is true but the
> next address is 0xffffffbfbdf80000 which is not aligned to PUD_SIZE.
>
> In the correct condition, this should fallback to the next level
> kasan_remove_pmd_table() but the condition flow always continue to skip
> the unaligned part.
>
> Fix by correcting the condition when next and addr are neither aligned.
>
> Fixes: 0207df4fa1a86 ("kernel/memremap, kasan: make ZONE_DEVICE with work with KASAN")
> Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
> ---
>  mm/kasan/init.c | 20 ++++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> index 67051cfae41c..ae9158f7501f 100644
> --- a/mm/kasan/init.c
> +++ b/mm/kasan/init.c
> @@ -372,9 +372,10 @@ static void kasan_remove_pmd_table(pmd_t *pmd, unsigned long addr,
>
>                 if (kasan_pte_table(*pmd)) {
>                         if (IS_ALIGNED(addr, PMD_SIZE) &&
> -                           IS_ALIGNED(next, PMD_SIZE))
> +                           IS_ALIGNED(next, PMD_SIZE)) {
>                                 pmd_clear(pmd);
> -                       continue;
> +                               continue;
> +                       }
>                 }
>                 pte = pte_offset_kernel(pmd, addr);
>                 kasan_remove_pte_table(pte, addr, next);
> @@ -397,9 +398,10 @@ static void kasan_remove_pud_table(pud_t *pud, unsigned long addr,
>
>                 if (kasan_pmd_table(*pud)) {
>                         if (IS_ALIGNED(addr, PUD_SIZE) &&
> -                           IS_ALIGNED(next, PUD_SIZE))
> +                           IS_ALIGNED(next, PUD_SIZE)) {
>                                 pud_clear(pud);
> -                       continue;
> +                               continue;
> +                       }
>                 }
>                 pmd = pmd_offset(pud, addr);
>                 pmd_base = pmd_offset(pud, 0);
> @@ -423,9 +425,10 @@ static void kasan_remove_p4d_table(p4d_t *p4d, unsigned long addr,
>
>                 if (kasan_pud_table(*p4d)) {
>                         if (IS_ALIGNED(addr, P4D_SIZE) &&
> -                           IS_ALIGNED(next, P4D_SIZE))
> +                           IS_ALIGNED(next, P4D_SIZE)) {
>                                 p4d_clear(p4d);
> -                       continue;
> +                               continue;
> +                       }
>                 }
>                 pud = pud_offset(p4d, addr);
>                 kasan_remove_pud_table(pud, addr, next);
> @@ -456,9 +459,10 @@ void kasan_remove_zero_shadow(void *start, unsigned long size)
>
>                 if (kasan_p4d_table(*pgd)) {
>                         if (IS_ALIGNED(addr, PGDIR_SIZE) &&
> -                           IS_ALIGNED(next, PGDIR_SIZE))
> +                           IS_ALIGNED(next, PGDIR_SIZE)) {
>                                 pgd_clear(pgd);
> -                       continue;
> +                               continue;
> +                       }
>                 }
>
>                 p4d = p4d_offset(pgd, addr);
> --
> 2.25.1

Andrey, could you please take a look at this change?

Thanks!