Re: KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack overflow with CONFIG_KASAN

From	Andrey Ryabinin <ryabinin.a.a@gmail.com>
Newsgroups	linux.kernel
Subject	Re: KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack overflow with CONFIG_KASAN
Date	2017-02-08 16:30 +0100
Message-ID	<t8ClY-20B-27@gated-at.bofh.it> (permalink)
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2017-02-08 16:10 GMT+03:00 Arnd Bergmann <arnd@arndb.de>:
> On Wed, Feb 8, 2017 at 1:24 PM, Johannes Berg <johannes@sipsolutions.net> wrote:

>
>> Btw, what's causing this to start with? Can't the compiler reuse the
>> stack places?
>
> I have no idea. It's trying to find out of bounds accesses for
> objects on the stack, so maybe it gives each variable a separate
> stack location in order to see which one caused problems?
>

If compiler cannot prove that access to the local variable is valid it
will add redzones around that variable
to be able to detect out of bounds accesses.

For example:
    static inline int nla_put_u8(struct sk_buff *skb, int attrtype, u8 value)
    {
           return nla_put(skb, attrtype, sizeof(u8), &value);
    }
compiler will surround 'value' with redzones to catch potential oob
access in nla_put().


Another way to fix this, would be something like this:

#ifdef CONFIG_KASAN
/* don't bloat stack */
#define __noinline_for_kasan    __noinline __maybe_unused
#else
#define __noinline_for_kasan    inline
#endif

static __noinline_for_kasan int nla_put_u8(struct sk_buff *skb, int
attrtype, u8 value)
{
       return nla_put(skb, attrtype, sizeof(u8), &value);
}

Thread

[PATCH] [net-next?] hns: avoid stack overflow with CONFIG_KASAN Arnd Bergmann <arnd@arndb.de> - 2017-02-03 17:40 +0100
  Re: [PATCH] [net-next?] hns: avoid stack overflow with CONFIG_KASAN David Miller <davem@davemloft.net> - 2017-02-06 18:10 +0100
    KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack overflow with CONFIG_KASAN Arnd Bergmann <arnd@arndb.de> - 2017-02-08 13:10 +0100
      Re: KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack  overflow with CONFIG_KASAN Johannes Berg <johannes@sipsolutions.net> - 2017-02-08 14:00 +0100
        Re: KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack overflow  with CONFIG_KASAN Arnd Bergmann <arnd@arndb.de> - 2017-02-08 14:20 +0100
          Re: KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack overflow  with CONFIG_KASAN Andrey Ryabinin <ryabinin.a.a@gmail.com> - 2017-02-08 16:30 +0100
        RE: KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack  overflow with CONFIG_KASAN David Laight <David.Laight@ACULAB.COM> - 2017-02-08 17:50 +0100
      Re: KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack  overflow with CONFIG_KASAN David Miller <davem@davemloft.net> - 2017-02-08 17:40 +0100

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