From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752225AbbCJIBu (ORCPT ); Tue, 10 Mar 2015 04:01:50 -0400 Received: from cantor2.suse.de ([195.135.220.15]:44436 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750882AbbCJIBs (ORCPT ); Tue, 10 Mar 2015 04:01:48 -0400 Date: Tue, 10 Mar 2015 09:00:24 +0100 From: Borislav Petkov To: Yinghai Lu Cc: Matt Fleming , "H. Peter Anvin" , Ingo Molnar , Kees Cook , Baoquan He , Thomas Gleixner , Jiri Kosina , linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org Subject: Re: [PATCH v3 2/7] x86, boot: Move ZO to end of buffer Message-ID: <20150310080024.GB3535@pd.tnic> References: <1425766041-6551-1-git-send-email-yinghai@kernel.org> <1425766041-6551-3-git-send-email-yinghai@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1425766041-6551-3-git-send-email-yinghai@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Final patch: --- From: Yinghai Lu Date: Sat, 7 Mar 2015 14:07:16 -0800 Subject: [PATCH] x86/setup: Move compressed kernel to the end of the buffer Boris found that passing KASLR status through setup_data from the boot stage cannot be used later in the kernel stage, see commit f47233c2d34f ("x86/mm/ASLR: Propagate base load address calculation") Here's some background: The boot loader allocates a buffer of size init_size in concordance with the value passed in the setup header and it loads the compressed, i.e. first kernel (arch/x86/boot/compressed/vmlinux) in it. First kernel then moves itself somewhere around the middle of the buffer at z_extract_offset to make sure that the decompressor does not overwrite input data. After the decompressor is finished, kernel proper (vmlinux) uses the whole buffer from the beginning and the compressed kernel's code and data section is overlapped with the kernel proper's bss section. Later on, clear_bss() in kernel proper clears .bss before code in arch/x86/kernel/setup.c can access setup_data passed in the first, compressed kernel. To make sure that data survives, we should avoid the overlapping. As a first step, move the first kernel closer to the end of the buffer instead of the middle. As a result, this will place first kernel's data area out of kernel proper's .bss area. This way we can find out where the data section of the copied first kernel is instead of guessing. In addition, it will make the KASLR mem_avoid array preparation for the search of a fitting buffer much simpler. While at it, rename z_extract_offset to z_min_extract_offset as it is actually the minimum extract offset now. In order to keep the final extract offset page-aligned we need to make both kernels' _end markers page-aligned too so that init_size is page-aligned as a result. Signed-off-by: Yinghai Lu Cc: "H. Peter Anvin" Cc: Matt Fleming Cc: Kees Cook Cc: Thomas Gleixner Cc: Jiri Kosina Cc: linux-efi@vger.kernel.org Cc: Ingo Molnar Cc: Baoquan He Fixes: f47233c2d34f ("x86/mm/ASLR: Propagate base load address calculation") Link: http://lkml.kernel.org/r/1425766041-6551-3-git-send-email-yinghai@kernel.org [ Commit message massively rewritten ] Signed-off-by: --- arch/x86/boot/compressed/head_32.S | 11 +++++++++-- arch/x86/boot/compressed/head_64.S | 8 ++++++-- arch/x86/boot/compressed/mkpiggy.c | 7 ++----- arch/x86/boot/compressed/vmlinux.lds.S | 1 + arch/x86/boot/header.S | 2 +- arch/x86/kernel/asm-offsets.c | 1 + arch/x86/kernel/vmlinux.lds.S | 1 + 7 files changed, 21 insertions(+), 10 deletions(-) diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S index cbed1407a5cd..a9b56f1d8e75 100644 --- a/arch/x86/boot/compressed/head_32.S +++ b/arch/x86/boot/compressed/head_32.S @@ -147,7 +147,9 @@ preferred_addr: 1: /* Target address to relocate to for decompression */ - addl $z_extract_offset, %ebx + movl BP_init_size(%esi), %eax + subl $_end, %eax + addl %eax, %ebx /* Set up the stack */ leal boot_stack_end(%ebx), %esp @@ -208,8 +210,13 @@ relocated: */ /* push arguments for decompress_kernel: */ pushl $z_output_len /* decompressed length */ - leal z_extract_offset_negative(%ebx), %ebp + + movl BP_init_size(%esi), %eax + subl $_end, %eax + movl %ebx, %ebp + subl %eax, %ebp pushl %ebp /* output address */ + pushl $z_input_len /* input_len */ leal input_data(%ebx), %eax pushl %eax /* input_data */ diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index 2884e0c3e8a5..69015b576cf6 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -101,7 +101,9 @@ ENTRY(startup_32) 1: /* Target address to relocate to for decompression */ - addl $z_extract_offset, %ebx + movl BP_init_size(%esi), %eax + subl $_end, %eax + addl %eax, %ebx /* * Prepare for entering 64 bit mode @@ -329,7 +331,9 @@ preferred_addr: 1: /* Target address to relocate to for decompression */ - leaq z_extract_offset(%rbp), %rbx + movl BP_init_size(%rsi), %ebx + subl $_end, %ebx + addq %rbp, %rbx /* Set up the stack */ leaq boot_stack_end(%rbx), %rsp diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c index b669ab65bf6c..c03b0097ce58 100644 --- a/arch/x86/boot/compressed/mkpiggy.c +++ b/arch/x86/boot/compressed/mkpiggy.c @@ -80,11 +80,8 @@ int main(int argc, char *argv[]) printf("z_input_len = %lu\n", ilen); printf(".globl z_output_len\n"); printf("z_output_len = %lu\n", (unsigned long)olen); - printf(".globl z_extract_offset\n"); - printf("z_extract_offset = 0x%lx\n", offs); - /* z_extract_offset_negative allows simplification of head_32.S */ - printf(".globl z_extract_offset_negative\n"); - printf("z_extract_offset_negative = -0x%lx\n", offs); + printf(".globl z_min_extract_offset\n"); + printf("z_min_extract_offset = 0x%lx\n", offs); printf(".globl input_data, input_data_end\n"); printf("input_data:\n"); diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S index 34d047c98284..a80acabb80ec 100644 --- a/arch/x86/boot/compressed/vmlinux.lds.S +++ b/arch/x86/boot/compressed/vmlinux.lds.S @@ -70,5 +70,6 @@ SECTIONS _epgtable = . ; } #endif + . = ALIGN(PAGE_SIZE); /* keep size page-aligned */ _end = .; } diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S index 16ef02596db2..9bfab22efdf7 100644 --- a/arch/x86/boot/header.S +++ b/arch/x86/boot/header.S @@ -440,7 +440,7 @@ setup_data: .quad 0 # 64-bit physical pointer to pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr -#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset) +#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_min_extract_offset) #define VO_INIT_SIZE (VO__end - VO__text) #if ZO_INIT_SIZE > VO_INIT_SIZE #define INIT_SIZE ZO_INIT_SIZE diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c index 9f6b9341950f..0e8e4f7a31ce 100644 --- a/arch/x86/kernel/asm-offsets.c +++ b/arch/x86/kernel/asm-offsets.c @@ -66,6 +66,7 @@ void common(void) { OFFSET(BP_hardware_subarch, boot_params, hdr.hardware_subarch); OFFSET(BP_version, boot_params, hdr.version); OFFSET(BP_kernel_alignment, boot_params, hdr.kernel_alignment); + OFFSET(BP_init_size, boot_params, hdr.init_size); OFFSET(BP_pref_address, boot_params, hdr.pref_address); OFFSET(BP_code32_start, boot_params, hdr.code32_start); diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 00bf300fd846..a92d3dc2812a 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -325,6 +325,7 @@ SECTIONS __brk_limit = .; } + . = ALIGN(PAGE_SIZE); /* keep init size page-aligned */ _end = .; STABS_DEBUG -- 2.2.0.33.gc18b867 -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. --