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Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN

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On Mon, Mar 6, 2017 at 10:16 AM, Arend Van Spriel
<arend.vanspriel@broadcom.com> wrote:
> On 2-3-2017 17:38, Arnd Bergmann wrote:
>> The wlc_phy_table_write_nphy/wlc_phy_table_read_nphy functions always put an object
>> on the stack, which will each require a redzone with KASAN and lead to possible
>> stack overflow:
>>
>> drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c: In function 'wlc_phy_workarounds_nphy':
>> drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c:17135:1: warning: the frame size of 6312 bytes is larger than 1000 bytes [-Wframe-larger-than=]
>
> Looks like this warning text ended up in the wrong commit message. Got
> me confused for a sec :-p

What's wrong about the warning?

>> This marks the two functions as noinline_for_kasan, avoiding the problem entirely.
>
> Frankly I seriously dislike annotating code for the sake of some
> (dynamic) memory analyzer. To me the whole thing seems rather
> unnecessary. If the code passes the 2048 stack limit without KASAN it
> would seem the limit with KASAN should be such that no warning is given.
> I suspect that it is rather difficult to predict the additional size of
> the instrumentation code and on some systems there might be a real issue
> with increased stack usage.

The frame sizes don't normally change that much. There are a couple of
drivers like brcmsmac that repeatedly call an inline function which has
a local variable that it passes by reference to an extern function.

While normally those variables share a stack location, KASAN forces
each instance to its own location and adds (in this case) 80 bytes of
redzone around it to detect out-of-bounds access.

While most drivers are fine with a 1500 byte warning limit, increasing
the limit to 7kb would silence brcmsmac (unless more registers
are accessed from wlc_phy_workarounds_nphy) but also risk a
stack overflow to go unnoticed.

    Arnd

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[PATCH 00/26] bring back stack frame warning with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
    Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-06 10:50 +0100
      Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-06 12:00 +0100
        Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-06 12:20 +0100
          Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-06 12:20 +0100
            Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-06 12:40 +0100
  [PATCH 15/26] [media] tuners: i2c: reduce stack usage for tuner_i2c_xfer_* Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 11/26] rtlwifi: reduce stack usage for KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 04/26] tty: kbd: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 12/26] wl3501_cs: reduce stack size for KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 09/26] brcmsmac: split up wlc_phy_workarounds_nphy Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
    Re: [PATCH 09/26] brcmsmac: split up wlc_phy_workarounds_nphy Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-06 10:40 +0100
  [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
    Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Alexander Potapenko <glider@google.com> - 2017-03-03 15:00 +0100
      Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Alexander Potapenko <glider@google.com> - 2017-03-03 15:40 +0100
        Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Arnd Bergmann <arnd@arndb.de> - 2017-03-03 16:10 +0100
      Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Arnd Bergmann <arnd@arndb.de> - 2017-03-03 15:40 +0100
    RE: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation David Laight <David.Laight@ACULAB.COM> - 2017-03-03 18:10 +0100
  [PATCH 05/26] netlink: mark nla_put_{u8,u16,u32} noinline_for_kasan Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 08/26] brcmsmac: make some local variables 'static const' to reduce stack size Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
    Re: [PATCH 08/26] brcmsmac: make some local variables 'static const'  to reduce stack size Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-06 10:40 +0100
      Re: [PATCH 08/26] brcmsmac: make some local variables 'static const' to reduce stack size Kalle Valo <kvalo@codeaurora.org> - 2017-03-06 17:40 +0100
        Re: [PATCH 08/26] brcmsmac: make some local variables 'static const'  to reduce stack size Arnd Bergmann <arnd@arndb.de> - 2017-03-06 22:40 +0100
          Re: [PATCH 08/26] brcmsmac: make some local variables 'static const' to reduce stack size Kalle Valo <kvalo@codeaurora.org> - 2017-03-07 10:50 +0100
            Re: [PATCH 08/26] brcmsmac: make some local variables 'static const'  to reduce stack size Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-07 11:10 +0100
  [PATCH 22/26] drm/i915/gvt: don't overflow the kernel stack with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:40 +0100
  Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Joe Perches <joe@perches.com> - 2017-03-02 19:00 +0100
    Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Joe Perches <joe@perches.com> - 2017-03-02 23:50 +0100
      Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-03 00:10 +0100
        Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Joe Perches <joe@perches.com> - 2017-03-03 01:00 +0100
    Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-03 00:00 +0100
  [PATCH 24/26] ocfs2: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 20:10 +0100
  [PATCH 23/26] mtd: cfi: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 20:20 +0100
  [PATCH 18/26] [media] i2c: cx25840: avoid stack overflow with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 23:30 +0100
  Re: [PATCH 00/26] bring back stack frame warning with KASAN Alexander Potapenko <glider@google.com> - 2017-03-03 13:30 +0100
    Re: [PATCH 00/26] bring back stack frame warning with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-03 14:00 +0100
  Re: [PATCH 10/26] brcmsmac: reindent split functions Kalle Valo <kvalo@codeaurora.org> - 2017-03-06 17:50 +0100

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