linux-kernel - Re: [PATCH RFC 2/8] arm64: stacktrace: Add arch_within_stack

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Date:   Mon, 18 Apr 2022 14:59:49 -0700
From:   Kees Cook <keescook@...omium.org>
To:     He Zhe <zhe.he@...driver.com>
Cc:     catalin.marinas@....com, will@...nel.org, mark.rutland@....com,
        tglx@...utronix.de, bp@...en8.de, dave.hansen@...ux.intel.com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, benh@...nel.crashing.org, paulus@...ba.org,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com, hpa@...or.com,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 2/8] arm64: stacktrace: Add arch_within_stack_frames

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.

Thanks!

-Kees

-- 
Kees Cook