From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 31D33495E1; Fri, 15 Dec 2023 21:17:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="GChepM/d" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1702675024; x=1734211024; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=n2+i7SehULhdMeNNvXfQ4W2QO4fq12pE9TACQPTaBSk=; b=GChepM/dYLFP9+eKZC7dmKjnXPFS+IV5zbPogiU0T67MjtrbSDwvlSwY waOswDrZd6J0CS+COfB8pZLutc2gZ6bXbKwpHPQOwik3xrtXEJfouk3s5 qZ+sbCsPDTJ9ISwSkjtb6nW3uCINL8r+O1NzlcUAAuGCcpGnWFoIp+hMb xJFL1bCJ9NVTfhnri/w9PG0WhEKqmCow63Z500kfP/eUQVYPbYNHjx8jp s2EHeN6YBJt7axYU4TLCluh26i0zw+ENpON78pRX4efSqoXaQ09lJ4Vdw 7WJWHF5jKyZp5gPNZm0wz7NwU7ayW7vS4d54pTg0iyQ2zlNo/q7VDcXeV w==; X-IronPort-AV: E=McAfee;i="6600,9927,10925"; a="2151943" X-IronPort-AV: E=Sophos;i="6.04,279,1695711600"; d="scan'208";a="2151943" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmvoesa105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Dec 2023 13:17:02 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10925"; a="803841033" X-IronPort-AV: E=Sophos;i="6.04,279,1695711600"; d="scan'208";a="803841033" Received: from jwaxmons-hp.amr.corp.intel.com (HELO [10.212.150.221]) ([10.212.150.221]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Dec 2023 13:17:01 -0800 Message-ID: Date: Fri, 15 Dec 2023 13:17:00 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] kexec: allocate kernel above bzImage's pref_address Content-Language: en-US To: Chris Koch , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-doc@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org Cc: Cloud Hsu References: <20231215190521.3796022-1-chrisko@google.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: <20231215190521.3796022-1-chrisko@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/15/23 11:05, Chris Koch wrote: > A relocatable kernel will relocate itself to pref_address if it is > loaded below pref_address. This means a booted kernel may be relocating > itself to an area with reserved memory on modern systems, potentially > clobbering arbitrary data that may be important to the system. > > This is often the case, as the default value of PHYSICAL_START is > 0x1000000 and kernels are typically loaded at 0x100000 or above by > bootloaders like iPXE or kexec. GRUB behaves like this patch does. > > Also fixes the documentation around pref_address and PHYSICAL_START to > be accurate. Are you reporting a bug and is this a bug fix? It's not super clear from the changelog. > diff --git a/Documentation/arch/x86/boot.rst b/Documentation/arch/x86/boot.rst > index 22cc7a040dae..49bea8986620 100644 > --- a/Documentation/arch/x86/boot.rst > +++ b/Documentation/arch/x86/boot.rst > @@ -878,7 +878,8 @@ Protocol: 2.10+ > address if possible. > > A non-relocatable kernel will unconditionally move itself and to run > - at this address. > + at this address. A relocatable kernel will move itself to this address if it > + loaded below this address. I think we should avoid saying the same things over and over again in different spots. Here, it doesn't really help to enumerate the different interpretations of 'pref_address'. All that matters is that the bootloader can avoid the overhead of a later copy if it can place the kernel at 'pref_address'. The exact reasons that various kernels might decide to relocate are unimportant here. > ============ ======= > Field name: init_size > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 3762f41bb092..1370f43328d7 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -2109,11 +2109,11 @@ config PHYSICAL_START > help > This gives the physical address where the kernel is loaded. > > - If kernel is a not relocatable (CONFIG_RELOCATABLE=n) then > - bzImage will decompress itself to above physical address and > - run from there. Otherwise, bzImage will run from the address where > - it has been loaded by the boot loader and will ignore above physical > - address. > + If the kernel is not relocatable (CONFIG_RELOCATABLE=n) then bzImage > + will decompress itself to above physical address and run from there. > + Otherwise, bzImage will run from the address where it has been loaded > + by the boot loader. The only exception is if it is loaded below the > + above physical address, in which case it will relocate itself there. I kinda dislike how this is written. It's written almost like code where you're spelling out the conditions. I prefer something much higher-level. This gives a minimum physical address at which the kernel can be loaded. CONFIG_RELOCATABLE=n kernels will be decompressed to and must run at PHYSICAL_START exactly. CONFIG_RELOCATABLE=y kernels can run at any address above PHYSICAL_START. If a kernel is loaded below PHYSICAL_START, it will relocate itself to PHYSICAL_START. > In normal kdump cases one does not have to set/change this option > as now bzImage can be compiled as a completely relocatable image > diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c > index a61c12c01270..5dcd232d58bf 100644 > --- a/arch/x86/kernel/kexec-bzimage64.c > +++ b/arch/x86/kernel/kexec-bzimage64.c > @@ -498,7 +498,10 @@ static void *bzImage64_load(struct kimage *image, char *kernel, > kbuf.bufsz = kernel_len - kern16_size; > kbuf.memsz = PAGE_ALIGN(header->init_size); > kbuf.buf_align = header->kernel_alignment; > - kbuf.buf_min = MIN_KERNEL_LOAD_ADDR; > + if (header->pref_address < MIN_KERNEL_LOAD_ADDR) > + kbuf.buf_min = MIN_KERNEL_LOAD_ADDR; > + else > + kbuf.buf_min = header->pref_address; > kbuf.mem = KEXEC_BUF_MEM_UNKNOWN; > ret = kexec_add_buffer(&kbuf); > if (ret) Comment, please. It isn't clear from this hunk why or how this fixes the bug. How does this manage to avoid clobbering reserved areas?