[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3 09/11] fuzz/x86emul: update fuzzer
On Fri, Feb 03, 2017 at 12:04:04AM -0700, Jan Beulich wrote: > >>> On 02.02.17 at 18:12, <wei.liu2@xxxxxxxxxx> wrote: > > On Thu, Feb 02, 2017 at 10:01:46AM -0700, Jan Beulich wrote: > >> >>> On 02.02.17 at 17:50, <wei.liu2@xxxxxxxxxx> wrote: > >> > On Thu, Feb 02, 2017 at 05:20:56AM -0700, Jan Beulich wrote: > >> >> >>> On 01.02.17 at 13:02, <wei.liu2@xxxxxxxxxx> wrote: > >> >> > +static int _fuzz_read_msr( > >> >> > + unsigned int reg, > >> >> > + uint64_t *val, > >> >> > + struct x86_emulate_ctxt *ctxt) > >> >> > +{ > >> >> > + unsigned int idx; > >> >> > + > >> >> > + switch ( reg ) > >> >> > + { > >> >> > + case MSR_TSC_AUX: > >> >> > + case MSR_IA32_TSC: > >> >> > + return data_read("read_msr", val, sizeof(*val)); > >> >> > >> >> Strictly speaking the above applies to TSC_AUX too. And TSC should > >> >> return monotonically increasing values. I don't think though that > >> >> producing random output here matters right now. A comment may > >> >> be worthwhile. > >> >> > >> > > >> > Right, I will add the following: > >> > > >> > /* > >> > * TSC should return monotonically increasing values, but > >> > * returning random values is fine in fuzzer. > >> > */ > >> > >> What about TSC_AUX then? > >> > > > > What model would you like it to follow? I suppose returning random value > > is also fine? I.e. I should just add TSC_AUX to the comment as well. > > That's one option. Even better would be to consistently return > the same (possibly random) value. But the value itself isn't being > looked at by the emulator, and iirc the MSR also isn't ever being > read multiple times, so it really doesn't matter as long as the > caller(s) of x86_emulate() do(es)n't care. Returning consistent doable but that would involve rewriting a significant portion of the fuzzer. Let's leave it for another day. I will modify the comment as follows: /* * TSC should return monotonically increasing values, TSC_AUX should * preferably return consistent value, but returning random values * is fine in fuzzer. */ > > Jan > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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