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[34.38.134.32]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3ee0fbc7478sm8458140f8f.38.2025.09.19.09.40.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Sep 2025 09:40:01 -0700 (PDT) Date: Fri, 19 Sep 2025 16:39:59 +0000 From: Adrian =?utf-8?Q?Barna=C5=9B?= To: Ard Biesheuvel Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Catalin Marinas , Will Deacon , Dylan Hatch , Mark Rutland , Fanqin Cui Subject: Re: [PATCH 2/2] arch: arm64: Reject modules with internal alternative callbacks Message-ID: References: <20250919122321.946462-1-abarnas@google.com> <20250919122321.946462-3-abarnas@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Sep 19, 2025 at 05:01:09PM +0200, Ard Biesheuvel wrote: >Hi Adrian, > >On Fri, 19 Sept 2025 at 14:23, Adrian Barnaś wrote: >> >> During module loading, check if there is a callback function used by the >> alternatives specified in the '.altinstruction' ELF section and block >> loading the module if such a function is present. >> > >Why? > >AIUI, the issue being addressed is the fact that we cannot yet execute >code from the module itself when alternatives are being applied, and >so the callback must live in the core kernel, or in another module. > >So this is a really big hammer, given that it disallows all callback >alternatives, including ones that we could easily support. Yes, it is true. What about we check if cb resides in kernel .text using core_kernel_text()? Pointer should be valid already since applying alternatives is done after relocation. We can shrink the hammer a bit. Then we allow the callback from inside the kernel to be called from the module but reject modules with callbacks that are invalid. Thanks, Adrian