linux-kernel - Re: [PATCH 0/5] riscv: SCS support

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Date:   Mon, 14 Aug 2023 11:33:46 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Kees Cook <keescook@...omium.org>, Guo Ren <guoren@...nel.org>,
        Deepak Gupta <debug@...osinc.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        linux-riscv@...ts.infradead.org, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] riscv: SCS support

On Mon, Aug 14, 2023 at 10:59 AM Nathan Chancellor <nathan@...nel.org> wrote:
> I took this series for a spin on top of 6.5-rc6 with both LLVM 18 (built
> within the past couple of days) and LLVM 17.0.0-rc2 but it seems that
> the CFI_BACKWARDS LKDTM test does not pass with
> CONFIG_SHADOW_CALL_STACK=y.
>
>   [   73.324652] lkdtm: Performing direct entry CFI_BACKWARD
>   [   73.324900] lkdtm: Attempting unchecked stack return address redirection ...
>   [   73.325178] lkdtm: Eek: return address mismatch! 0000000000000002 != ffffffff80614982
>   [   73.325478] lkdtm: FAIL: stack return address manipulation failed!
>
> Does the test need to be adjusted or is there some other issue?

The test doesn't work on RISC-V. set_return_addr_unchecked thinks 0x2
is the return address, so I assume the __builtin_frame_address logic
isn't quite right here. Kees, any thoughts?

Sami