From e1bfa87399e372446454ecbaeba2800f0a385733 Mon Sep 17 00:00:00 2001 From: Thomas Lendacky Date: Wed, 19 Jun 2019 18:40:59 +0000 Subject: [PATCH] x86/mm: Create a workarea in the kernel for SME early encryption MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In order for the kernel to be encrypted "in place" during boot, a workarea outside of the kernel must be used. This SME workarea used during early encryption of the kernel is situated on a 2MB boundary after the end of the kernel text, data, etc. sections (_end). This works well during initial boot of a compressed kernel because of the relocation used for decompression of the kernel. But when performing a kexec boot, there's a chance that the SME workarea may not be mapped by the kexec pagetables or that some of the other data used by kexec could exist in this range. Create a section for SME in vmlinux.lds.S. Position it after "_end", which is after "__end_of_kernel_reserve", so that the memory will be reclaimed during boot and since this area is all zeroes, it compresses well. This new section will be part of the kernel image, so kexec will account for it in pagetable mappings and placement of data after the kernel. Here's an example of a kernel size without and with the SME section: without: vmlinux: 36,501,616 bzImage: 6,497,344 100000000-47f37ffff : System RAM 1e4000000-1e47677d4 : Kernel code (0x7677d4) 1e47677d5-1e4e2e0bf : Kernel data (0x6c68ea) 1e5074000-1e5372fff : Kernel bss (0x2fefff) with: vmlinux: 44,419,408 bzImage: 6,503,136 880000000-c7ff7ffff : System RAM 8cf000000-8cf7677d4 : Kernel code (0x7677d4) 8cf7677d5-8cfe2e0bf : Kernel data (0x6c68ea) 8d0074000-8d0372fff : Kernel bss (0x2fefff) Signed-off-by: Tom Lendacky Signed-off-by: Borislav Petkov Reviewed-by: Baoquan He Reviewed-by: Dave Hansen Tested-by: Lianbo Jiang Cc: Andy Lutomirski Cc: Brijesh Singh Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Joerg Roedel Cc: Kees Cook Cc: Nick Desaulniers Cc: Peter Zijlstra Cc: "Rafael Ávila de Espíndola" Cc: Sami Tolvanen Cc: Thomas Gleixner Cc: "x86@kernel.org" Link: https://lkml.kernel.org/r/3c483262eb4077b1654b2052bd14a8d011bffde3.1560969363.git.thomas.lendacky@amd.com --- arch/x86/kernel/vmlinux.lds.S | 25 +++++++++++++++++++++++++ arch/x86/mm/mem_encrypt_identity.c | 22 ++++++++++++++++++++-- 2 files changed, 45 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index ca2252ca6ad7..147cd020516a 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -387,6 +387,31 @@ SECTIONS . = ALIGN(PAGE_SIZE); /* keep VO_INIT_SIZE page aligned */ _end = .; +#ifdef CONFIG_AMD_MEM_ENCRYPT + /* + * Early scratch/workarea section: Lives outside of the kernel proper + * (_text - _end). + * + * Resides after _end because even though the .brk section is after + * __end_of_kernel_reserve, the .brk section is later reserved as a + * part of the kernel. Since it is located after __end_of_kernel_reserve + * it will be discarded and become part of the available memory. As + * such, it can only be used by very early boot code and must not be + * needed afterwards. + * + * Currently used by SME for performing in-place encryption of the + * kernel during boot. Resides on a 2MB boundary to simplify the + * pagetable setup used for SME in-place encryption. + */ + . = ALIGN(HPAGE_SIZE); + .init.scratch : AT(ADDR(.init.scratch) - LOAD_OFFSET) { + __init_scratch_begin = .; + *(.init.scratch) + . = ALIGN(HPAGE_SIZE); + __init_scratch_end = .; + } +#endif + STABS_DEBUG DWARF_DEBUG diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c index 4aa9b1480866..6a8dd483f7d9 100644 --- a/arch/x86/mm/mem_encrypt_identity.c +++ b/arch/x86/mm/mem_encrypt_identity.c @@ -73,6 +73,19 @@ struct sme_populate_pgd_data { unsigned long vaddr_end; }; +/* + * This work area lives in the .init.scratch section, which lives outside of + * the kernel proper. It is sized to hold the intermediate copy buffer and + * more than enough pagetable pages. + * + * By using this section, the kernel can be encrypted in place and it + * avoids any possibility of boot parameters or initramfs images being + * placed such that the in-place encryption logic overwrites them. This + * section is 2MB aligned to allow for simple pagetable setup using only + * PMD entries (see vmlinux.lds.S). + */ +static char sme_workarea[2 * PMD_PAGE_SIZE] __section(.init.scratch); + static char sme_cmdline_arg[] __initdata = "mem_encrypt"; static char sme_cmdline_on[] __initdata = "on"; static char sme_cmdline_off[] __initdata = "off"; @@ -314,8 +327,13 @@ void __init sme_encrypt_kernel(struct boot_params *bp) } #endif - /* Set the encryption workarea to be immediately after the kernel */ - workarea_start = kernel_end; + /* + * We're running identity mapped, so we must obtain the address to the + * SME encryption workarea using rip-relative addressing. + */ + asm ("lea sme_workarea(%%rip), %0" + : "=r" (workarea_start) + : "p" (sme_workarea)); /* * Calculate required number of workarea bytes needed: