Messages in this thread | | | From | Arnd Bergmann <> | Date | Mon, 6 Mar 2017 11:38:00 +0100 | Subject | 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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