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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432bd5df939sm37629155f8f.21.2026.01.12.02.47.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 02:47:48 -0800 (PST) Date: Mon, 12 Jan 2026 10:47:46 +0000 From: David Laight To: "H. Peter Anvin" Cc: Ard Biesheuvel , linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Josh Poimboeuf , Peter Zijlstra , Kees Cook , Uros Bizjak , Brian Gerst , linux-hardening@vger.kernel.org Subject: Re: [RFC/RFT PATCH 04/19] x86: Make the 64-bit bzImage always physically relocatable Message-ID: <20260112104746.6521740c@pumpkin> In-Reply-To: <3f2e8d7c-6029-49ef-8e31-a3eb5efb385b@zytor.com> References: <20260108092526.28586-21-ardb@kernel.org> <20260108092526.28586-25-ardb@kernel.org> <3f2e8d7c-6029-49ef-8e31-a3eb5efb385b@zytor.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sun, 11 Jan 2026 20:01:02 -0800 "H. Peter Anvin" wrote: > On 2026-01-08 01:25, Ard Biesheuvel wrote: > > On x86_64, the physical placement of the kernel is independent from its > > mapping in the 'High Kernel Mapping' range. This means that even a > > position dependent kernel built without boot-time relocation support can > > run from any suitably aligned physical address, and there is no need to > > make this behavior dependent on whether or not the kernel is virtually > > relocatable. > > > > On i386, the situation is different, given that the physical and virtual > > load offsets must be equal, and so only a relocatable kernel can be > > loaded at a physical address that deviates from its build-time default. > > > > Clarify this in Kconfig and in the code, and advertise the 64-bit > > bzImage as loadable at any physical offset regardless of whether > > CONFIG_RELOCATABLE is set. In practice, this makes little difference, > > given that it defaults to 'y' and is a prerequisite for EFI_STUB and > > RANDOMIZE_BASE, but it will help with some future refactoring of the > > relocation code. > > > > I don't see any reason to support non-relocatable kernels anymore. In fact, in > a patchset I am working on I have already removed it. For just 64bit, or 32bit as well? The 'bloat' for 32bit will be higher due to the lack of pc-relative addressing. David > > -hpa > >