On Thu, Jun 1, 2017 at 7:00 PM, Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote: > > > On 06/01/2017 07:59 PM, Andrey Ryabinin wrote: >> >> >> On 06/01/2017 07:52 PM, Mark Rutland wrote: >>> On Thu, Jun 01, 2017 at 06:45:32PM +0200, Dmitry Vyukov wrote: >>>> On Thu, Jun 1, 2017 at 6:34 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote: >>>>> On Thu, Jun 01, 2017 at 07:23:37PM +0300, Andrey Ryabinin wrote: >>>>>> We used to read several bytes of the shadow memory in advance. >>>>>> Therefore additional shadow memory mapped to prevent crash if >>>>>> speculative load would happen near the end of the mapped shadow memory. >>>>>> >>>>>> Now we don't have such speculative loads, so we no longer need to map >>>>>> additional shadow memory. >>>>> >>>>> I see that patch 1 fixed up the Linux helpers for outline >>>>> instrumentation. >>>>> >>>>> Just to check, is it also true that the inline instrumentation never >>>>> performs unaligned accesses to the shadow memory? >>>> >> >> Correct, inline instrumentation assumes that all accesses are properly aligned as it >> required by C standard. I knew that the kernel violates this rule in many places, >> therefore I decided to add checks for unaligned accesses in outline case. >> >> >>>> Inline instrumentation generally accesses only a single byte. >>> >>> Sorry to be a little pedantic, but does that mean we'll never access the >>> additional shadow, or does that mean it's very unlikely that we will? >>> >>> I'm guessing/hoping it's the former! >>> >> >> Outline will never access additional shadow byte: https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm#unaligned-accesses > > s/Outline/inline of course. I suspect that actual implementations have diverged from that description. Trying to follow asan_expand_check_ifn in: https://gcc.gnu.org/viewcvs/gcc/trunk/gcc/asan.c?revision=246703&view=markup but it's not trivial. +Yuri, maybe you know off the top of your head if asan instrumentation in gcc ever accesses off-by-one shadow byte (i.e. 1 byte after actual object end)? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
