linux-kernel - Re: [PATCH v3 2/2] lkdtm: Add Shadow Call Stack tests

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Message-ID: <fc2fa0a9-eae8-edc4-f86f-b9056d93ee12@linux.alibaba.com>
Date:   Thu, 10 Mar 2022 18:46:29 -0800
From:   Dan Li <ashimida@...ux.alibaba.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     akpm@...ux-foundation.org, arnd@...db.de, catalin.marinas@....com,
        gregkh@...uxfoundation.org, linux@...ck-us.net,
        luc.vanoostenryck@...il.com, elver@...gle.com,
        mark.rutland@....com, masahiroy@...nel.org, ojeda@...nel.org,
        nathan@...nel.org, npiggin@...il.com, ndesaulniers@...gle.com,
        samitolvanen@...gle.com, shuah@...nel.org, tglx@...utronix.de,
        will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 2/2] lkdtm: Add Shadow Call Stack tests



On 3/9/22 12:16, Kees Cook wrote:
> On Mon, Mar 07, 2022 at 07:16:36AM -0800, Dan Li wrote:
>> But currently it still crashes when I try to enable
>> "-mbranch-protection=pac-ret+leaf+bti".
>>
>> Because the address of "&&redirected" is not encrypted under pac,
>> the autiasp check will fail when set_return_addr returns, and
>> eventually cause the function to crash when it returns to "&&redirected"
>> ("&&redirected" as a reserved label always seems to start with a bti j
>> insn).
> 
> Strictly speaking, this is entirely correct. :)
> 
>> For lkdtm, if we're going to handle both cases in one function, maybe
>> it would be better to turn off the -mbranch-protection=pac-ret+leaf+bti
>> and maybe also turn off -O2 options for the function :)
> 
> If we can apply a function attribute to turn off pac for the "does this
> work without protections", that should be sufficient.
> 

Got it, will do in the next version :)

Thanks,
Dan.