linux-kernel - Re: [PATCH V2 04/10] kasan: Don't use kasan shadow pointer in generic functions

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Date:	Thu, 27 Aug 2015 12:42:37 +0300
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	paulus@...ba.org, mpe@...erman.id.au,
	linuxppc-dev@...ts.ozlabs.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 04/10] kasan: Don't use kasan shadow pointer in generic functions

2015-08-26 11:54 GMT+03:00 Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>:
>
> Missed to cherry-pick the updated version of this patch, before sending
> the series out.
>
> commit aeb324e09d95c189eda4ce03790da94b535d1dfc
> Author: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Date:   Fri Aug 14 12:28:58 2015 +0530
>
>     kasan: Don't use kasan shadow pointer in generic functions
>
>     We can't use generic functions like print_hex_dump to access kasan
>     shadow region. This require us to setup another kasan shadow region
>     for the address passed (kasan shadow address). Most architecture won't
>     be able to do that. Hence make a copy of the shadow region row and
>     pass that to generic functions.
>
>     Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
>
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index d19d01823a68..60fdb0413f3b 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -166,14 +166,20 @@ static void print_shadow_for_address(const void *addr)
>         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
>                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
>                 char buffer[4 + (BITS_PER_LONG/8)*2];
> +               char shadow_buf[SHADOW_BYTES_PER_ROW];
>
>                 snprintf(buffer, sizeof(buffer),
>                         (i == 0) ? ">%p: " : " %p: ", kaddr);
> -
> +               /*
> +                * We should not pass a shadow pointer to generic
> +                * function, because generic functions may try to
> +                * kasan mapping for the passed address.

may try to *access* kasan mapping?

> +                */
> +               memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
>                 kasan_disable_current();
>                 print_hex_dump(KERN_ERR, buffer,
>                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
> -                       shadow_row, SHADOW_BYTES_PER_ROW, 0);
> +                       shadow_buf, SHADOW_BYTES_PER_ROW, 0);
>                 kasan_enable_current();
>
>                 if (row_is_guilty(shadow_row, shadow))
>
--
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