linux-hardening - Re: [PATCH v9 0/7] Introduce Kernel Control Flow Integrity ABI [PR107048]

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Message-ID: <269C524E-2FDB-4156-98FE-548993666B03@kernel.org>
Date: Thu, 01 Jan 2026 19:42:50 -0800
From: Kees Cook <kees@...nel.org>
To: Andrew Pinski <andrew.pinski@....qualcomm.com>
CC: Qing Zhao <qing.zhao@...cle.com>, Uros Bizjak <ubizjak@...il.com>,
 Joseph Myers <josmyers@...hat.com>, Richard Biener <rguenther@...e.de>,
 Jeff Law <jeffreyalaw@...il.com>, Andrew Pinski <pinskia@...il.com>,
 Jakub Jelinek <jakub@...hat.com>, Martin Uecker <uecker@...raz.at>,
 Peter Zijlstra <peterz@...radead.org>, Ard Biesheuvel <ardb@...nel.org>,
 Jan Hubicka <hubicka@....cz>, Richard Earnshaw <richard.earnshaw@....com>,
 Richard Sandiford <richard.sandiford@....com>,
 Marcus Shawcroft <marcus.shawcroft@....com>,
 Kyrylo Tkachov <kyrylo.tkachov@....com>, Kito Cheng <kito.cheng@...il.com>,
 Palmer Dabbelt <palmer@...belt.com>, Andrew Waterman <andrew@...ive.com>,
 Jim Wilson <jim.wilson.gcc@...il.com>, Dan Li <ashimida.1990@...il.com>,
 Sami Tolvanen <samitolvanen@...gle.com>,
 Ramon de C Valle <rcvalle@...gle.com>,
 Joao Moreira <joao@...rdrivepizza.com>,
 Nathan Chancellor <nathan@...nel.org>, Bill Wendling <morbo@...gle.com>,
 "Osterlund, Sebastian" <sebastian.osterlund@...el.com>,
 "Constable, Scott D" <scott.d.constable@...el.com>, gcc-patches@....gnu.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH v9 0/7] Introduce Kernel Control Flow Integrity ABI [PR107048]



On January 1, 2026 2:42:59 PM PST, Andrew Pinski <andrew.pinski@....qualcomm.com> wrote:
>On Tue, Dec 9, 2025 at 6:22 PM Kees Cook <kees@...nel.org> wrote:
>>
>> Hi,
>>
>> This series implements[1][2] the Linux Kernel Control Flow Integrity
>> ABI, which provides a function prototype based forward edge control flow
>> integrity protection by instrumenting every indirect call to check for
>> a hash value before the target function address. If the hash at the call
>> site and the hash at the target do not match, execution will trap.
>>
>> I'm hoping we can land front- and middle-end and do architectures as
>> they also pass review. What do folks think? I'd really like to get this
>> in a position where more people can test with GCC snapshots, etc.
>
>So looking back into the other implementation that was submitted a few
>years back (https://patchwork.sourceware.org/project/gcc/patch/20230325081117.93245-3-ashimida.1990@gmail.com/),
>a regnote (REG_CALL_CFI_TYPEID) was used instead of the wrapping with
>kfci rtl.
>I get the feeling a regnote would be better as there is less for the
>backend to deal with including new patterns.
>What do others think?

I started there and it created way too many problems that I had to continuously hack around. Switching to RTL solved all of it. (See v1 and v2 of this series where that was how it was implemented.)

-Kees


-- 
Kees Cook