[PATCH RFC 2/8] arm64: stacktrace: Add arch_within_stack_frames

[He Zhe]

On 4/19/22 05:59, Kees Cook wrote:
> On Mon, Apr 18, 2022 at 09:22:11PM +0800, He Zhe wrote:
>> This function checks if the given address range crosses frame boundary.
>> It is based on the existing x86 algorithm, but implemented via stacktrace.
>> This can be tested by USERCOPY_STACK_FRAME_FROM and
>> USERCOPY_STACK_FRAME_TO in lkdtm.
> Hi,
>
> Thanks for doing this implementation! One reason usercopy hardening
> didn't persue doing a "full" stacktrace was because it seemed relatively
> expensive. Did you do any usercopy-heavily workload testing to see if
> there was a noticeable performance impact?
>
> It would be nice to block the exposure of canaries and PAC bits, though,
> so I'm not opposed, but I'd like to get a better sense of how "heavy"
> this might be.

I just did some rough tests:
hackbench -s 512 -l 200 -g 15 -f 25 -P
Such line would hit arch_within_stack_frames at least 5000 times in my environment.
With hardened_usercopy=on, the execution time would be around 2.121 seconds(average for 30 times)
With hardened_usercopy=off, the execution time would be around 2.011 seconds(average for 30 times)

I'll test the original x86 way for arm64 tomorrow.

Any other workload needed to be run?

Thanks,
Zhe


>
> Thanks!
>
> -Kees
>