• Kees Cook's avatar
    gcc-plugins: structleak: Generalize to all variable types · 81a56f6d
    Kees Cook authored
    This adjusts structleak to also work with non-struct types when they
    are passed by reference, since those variables may leak just like
    anything else. This is exposed via an improved set of Kconfig options.
    (This does mean structleak is slightly misnamed now.)
    
    Building with CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL should give the
    kernel complete initialization coverage of all stack variables passed
    by reference, including padding (see lib/test_stackinit.c).
    
    Using CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE to count added initializations
    under defconfig:
    
    	..._BYREF:      5945 added initializations
    	..._BYREF_ALL: 16606 added initializations
    
    There is virtually no change to text+data size (both have less than 0.05%
    growth):
    
       text    data     bss     dec     hex filename
    19502103        5051456 1917000 26470559        193e89f vmlinux.stock
    19513412        5051456 1908808 26473676        193f4cc vmlinux.byref
    19516974        5047360 1900616 26464950        193d2b6 vmlinux.byref_all
    
    The measured performance difference is in the noise for hackbench and
    kernel build benchmarks:
    
    Stock:
    
    	5x hackbench -g 20 -l 1000
    	Mean:   10.649s
    	Std Dev: 0.339
    
    	5x kernel build (4-way parallel)
    	Mean:  261.98s
    	Std Dev: 1.53
    
    CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF:
    
    	5x hackbench -g 20 -l 1000
    	Mean:   10.540s
    	Std Dev: 0.233
    
    	5x kernel build (4-way parallel)
    	Mean:  260.52s
    	Std Dev: 1.31
    
    CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL:
    
    	5x hackbench -g 20 -l 1000
    	Mean:   10.320
    	Std Dev: 0.413
    
    	5x kernel build (4-way parallel)
    	Mean:  260.10
    	Std Dev: 0.86
    
    This does not yet solve missing padding initialization for structures
    on the stack that are never passed by reference (which should be a tiny
    minority). Hopefully this will be more easily addressed by upstream
    compiler fixes after clarifying the C11 padding initialization
    specification.
    Signed-off-by: default avatarKees Cook <keescook@chromium.org>
    Reviewed-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
    81a56f6d
Makefile.gcc-plugins 2.45 KB