On Fri, Dec 16, 2016 at 11:29 AM, Vaneet Narang <v.narang@xxxxxxxxxxx> wrote:
>
> Hi Andrey,
>
>
> There are times when requirement is only to find write issues so user should have flexibility to
> skip read instrumentation for better performance with KASAN enabled build to find realtime
> issues as well.
>
> >> crashes of false positives). CONFIG_KASAN_READS/WRITES is intended for
> >> situations when one wants to disable instrumentation wholesale.
> >>
> >
> >I'm talking about UBSAN_SANITIZE_ALL/KCOV_INSTRUMENT_ALL/GCOV_PROFILE_ALL
> >KASAN doesn't have something similar. I didn't add this because IMO it's not very useful for KASAN.
> >One may have a bug in instrumented code, but it can be easily missed if access is done in generic
> >code. Very simple example is passing invalid pointer in strcpy()
>
>
> Old toolchains already add asan hooks before strcpy, strcmp. Please check assembly generated
> for module with below code using gcc 4.9.
>
> static noinline void __init test_kasan_module(void) {
> strcpy(test, "testing strcpy");
> }
>
> 0000000000001108 <test_kasan_module>:
> 1108: a9bd7bfd stp x29, x30, [sp,#-48]!
> 110c: d28001e1 mov x1, #0xf // #15
> 1110: 910003fd mov x29, sp
> 1114: a90153f3 stp x19, x20, [sp,#16]
> 1118: 58000253 ldr x19, 1160 <test_kasan_module+0x58>
> 111c: f90013f5 str x21, [sp,#32]
> 1120: aa1303e0 mov x0, x19
> 1124: 94000000 bl 0 <__asan_loadN> // Instrumented Read of size 15
> 1128: 58000215 ldr x21, 1168 <test_kasan_module+0x60>
> 112c: d28001e1 mov x1, #0xf // #15
> 1130: 910042b4 add x20, x21, #0x10
> 1134: aa1403e0 mov x0, x20
> 1138: 94000000 bl 0 <__asan_storeN> // Instrumented Write of size 15
> 113c: f9400260 ldr x0, [x19]
> 1140: f9000aa0 str x0, [x21,#16]
> 1144: f8407260 ldr x0, [x19,#7]
> 1148: f80172a0 str x0, [x21,#23]
> 114c: a94153f3 ldp x19, x20, [sp,#16]
>
>
>
> Similar behaviour for strcmp, memset, memcpy ... but with latest compiler 6.2,
> this implementation is removed from compiler in this case we can define wrappers
> in kasan.c for these function like we are already doing for memcpy, memmove, memset
>
>
One option would be to simply compile kernel as:
$ make CC="gcc --param asan-instrument-reads=0"
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