linux-kernel - Re: [PATCH v2 1/4] arm64: kasan: don't populate vmalloc area for CONFIG_KASAN

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Date:   Wed, 3 Feb 2021 19:37:18 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Lecopzer Chen <lecopzer@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.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,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Mike Rapoport <rppt@...nel.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Robin Murphy <robin.murphy@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>
Subject: Re: [PATCH v2 1/4] arm64: kasan: don't populate vmalloc area for CONFIG_KASAN_VMALLOC

On Sat, 9 Jan 2021 at 11:33, Lecopzer Chen <lecopzer@...il.com> wrote:
>
> Linux support KAsan for VMALLOC since commit 3c5c3cfb9ef4da9
> ("kasan: support backing vmalloc space with real shadow memory")
>
> Like how the MODULES_VADDR does now, just not to early populate
> the VMALLOC_START between VMALLOC_END.
> similarly, the kernel code mapping is now in the VMALLOC area and
> should keep these area populated.
>
> Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>


This commit log text is a bit hard to follow. You are saying that the
vmalloc region is *not* backed with zero shadow or any default mapping
at all, right, and everything gets allocated on demand, just like is
the case for modules?

> ---
>  arch/arm64/mm/kasan_init.c | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index d8e66c78440e..39b218a64279 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -214,6 +214,7 @@ static void __init kasan_init_shadow(void)
>  {
>         u64 kimg_shadow_start, kimg_shadow_end;
>         u64 mod_shadow_start, mod_shadow_end;
> +       u64 vmalloc_shadow_start, vmalloc_shadow_end;
>         phys_addr_t pa_start, pa_end;
>         u64 i;
>
> @@ -223,6 +224,9 @@ static void __init kasan_init_shadow(void)
>         mod_shadow_start = (u64)kasan_mem_to_shadow((void *)MODULES_VADDR);
>         mod_shadow_end = (u64)kasan_mem_to_shadow((void *)MODULES_END);
>
> +       vmalloc_shadow_start = (u64)kasan_mem_to_shadow((void *)VMALLOC_START);
> +       vmalloc_shadow_end = (u64)kasan_mem_to_shadow((void *)VMALLOC_END);
> +


This and the below seems overly complicated, given that VMALLOC_START
== MODULES_END. Can we simplify this?

>         /*
>          * We are going to perform proper setup of shadow memory.
>          * At first we should unmap early shadow (clear_pgds() call below).
> @@ -241,12 +245,21 @@ static void __init kasan_init_shadow(void)
>
>         kasan_populate_early_shadow(kasan_mem_to_shadow((void *)PAGE_END),
>                                    (void *)mod_shadow_start);
> -       kasan_populate_early_shadow((void *)kimg_shadow_end,
> -                                  (void *)KASAN_SHADOW_END);
> +       if (IS_ENABLED(CONFIG_KASAN_VMALLOC)) {
> +               kasan_populate_early_shadow((void *)vmalloc_shadow_end,
> +                                           (void *)KASAN_SHADOW_END);
> +               if (vmalloc_shadow_start > mod_shadow_end)
> +                       kasan_populate_early_shadow((void *)mod_shadow_end,
> +                                                   (void *)vmalloc_shadow_start);
> +
> +       } else {
> +               kasan_populate_early_shadow((void *)kimg_shadow_end,
> +                                           (void *)KASAN_SHADOW_END);
> +               if (kimg_shadow_start > mod_shadow_end)
> +                       kasan_populate_early_shadow((void *)mod_shadow_end,
> +                                                   (void *)kimg_shadow_start);
> +       }
>
> -       if (kimg_shadow_start > mod_shadow_end)
> -               kasan_populate_early_shadow((void *)mod_shadow_end,
> -                                           (void *)kimg_shadow_start);
>
>         for_each_mem_range(i, &pa_start, &pa_end) {
>                 void *start = (void *)__phys_to_virt(pa_start);
> --
> 2.25.1
>