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Message-ID: <CAGXu5j+xk--24NqnkBAE+PRzR2eS+=Jc3Bu_rgHs5j2K0wPNng@mail.gmail.com>
Date: Mon, 7 Mar 2016 15:34:27 -0800
From: Kees Cook <keescook@...omium.org>
To: Baoquan He <bhe@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Yinghai Lu <yinghai@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>, Vivek Goyal <vgoyal@...hat.com>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Andy Lutomirski <luto@...nel.org>, lasse.collin@...aani.org,
Andrew Morton <akpm@...ux-foundation.org>,
Dave Young <dyoung@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
Borislav Petkov <bp@...e.de>,
Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v3 10/19] x86, 64bit: Set ident_mapping for kaslr
On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <bhe@...hat.com> wrote:
> From: Yinghai Lu <yinghai@...nel.org>
>
> Current aslr only support random in small range, from 16M to 1G. And
> new range still use old mapping. Also it does not support new range
> above 4G.
>
> We need to have ident mapping for the new range before we can do
> decompress to the new output, and later run them.
>
> In this patch, we add ident mapping for all needed range.
>
> At first, to support aslr to put random VO above 4G, we must set ident
> mapping for the new range when it come via startup_32 path.
>
> Secondly, when boot from 64bit bootloader, bootloader set ident mapping,
> and boot via ZO (arch/x86/boot/compressed/vmlinux) startup_64.
> Those pages for pagetable need to be avoided when we select new random
> VO (vmlinux) base. Otherwise decompressor would overwrite them during
> decompressing.
> First way would be: walk through pagetable and find out every page is used
> by pagetable for every mem_aovid checking but we will need extra code, and
> may need to increase mem_avoid array size to hold them.
> Other way would be: We can create new ident mapping instead, and pages for
> pagetable will come from _pagetable section of ZO, and they are in
> mem_avoid array already. In this way, we can reuse the code for ident
> mapping.
>
> The _pgtable will be shared by 32bit and 64bit path to reduce init_size,
> as now ZO _rodata to _end will contribute init_size.
>
> We need to increase pgt buffer size.
> When boot via startup_64, as we need to cover old VO, params, cmdline
> and new VO, in extreme case we could have them all cross 512G boundary,
> will need (2+2)*4 pages with 2M mapping. And need 2 for first 2M for vga
> ram. Plus one for level4. Total will be 19 pages.
> When boot via startup_32, aslr would move new VO above 4G, we need set
> extra ident mapping for new VO, pgt buffer come from _pgtable offset 6
> pages. Should only need (2+2) pages at most when it cross 512G boundary.
> So 19 pages could make both paths happy.
>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Jiri Kosina <jkosina@...e.cz>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Matt Fleming <matt.fleming@...el.com>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> ---
> arch/x86/boot/compressed/Makefile | 3 ++
> arch/x86/boot/compressed/aslr.c | 14 ++++++
> arch/x86/boot/compressed/head_64.S | 4 +-
> arch/x86/boot/compressed/misc.h | 11 +++++
> arch/x86/boot/compressed/misc_pgt.c | 91 +++++++++++++++++++++++++++++++++++++
> arch/x86/include/asm/boot.h | 19 ++++++++
> 6 files changed, 140 insertions(+), 2 deletions(-)
> create mode 100644 arch/x86/boot/compressed/misc_pgt.c
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 2e7c0ce..229604d 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -59,6 +59,9 @@ vmlinux-objs-y := $(obj)/vmlinux.lds $(obj)/head_$(BITS).o $(obj)/misc.o \
>
> vmlinux-objs-$(CONFIG_EARLY_PRINTK) += $(obj)/early_serial_console.o
> vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/aslr.o
> +ifdef CONFIG_X86_64
> + vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/misc_pgt.o
> +endif
>
> $(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
>
> diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
> index b93be03..35f2eac 100644
> --- a/arch/x86/boot/compressed/aslr.c
> +++ b/arch/x86/boot/compressed/aslr.c
> @@ -151,6 +151,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
> */
> mem_avoid[0].start = input;
> mem_avoid[0].size = (output + init_size) - input;
> + fill_pagetable(input, (output + init_size) - input);
These calls should juse use the .start and .size arguments instead of
the copy/paste.
>
> /* Avoid initrd. */
> initrd_start = (u64)real_mode->ext_ramdisk_image << 32;
> @@ -159,6 +160,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
> initrd_size |= real_mode->hdr.ramdisk_size;
> mem_avoid[1].start = initrd_start;
> mem_avoid[1].size = initrd_size;
> + /* don't need to set mapping for initrd */
>
> /* Avoid kernel command line. */
> cmd_line = (u64)real_mode->ext_cmd_line_ptr << 32;
> @@ -169,10 +171,19 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
> ;
> mem_avoid[2].start = cmd_line;
> mem_avoid[2].size = cmd_line_size;
> + fill_pagetable(cmd_line, cmd_line_size);
>
> /* Avoid params */
> mem_avoid[3].start = (unsigned long)real_mode;
> mem_avoid[3].size = sizeof(*real_mode);
> + fill_pagetable((unsigned long)real_mode, sizeof(*real_mode));
> +
> + /* don't need to set mapping for setup_data */
> +
> +#ifdef CONFIG_X86_VERBOSE_BOOTUP
> + /* for video ram */
> + fill_pagetable(0, PMD_SIZE);
> +#endif
> }
>
> /* Does this memory vector overlap a known avoided area? */
> @@ -330,6 +341,9 @@ unsigned char *choose_kernel_location(unsigned char *input,
> goto out;
>
> choice = random;
> +
> + fill_pagetable(choice, output_size);
> + switch_pagetable();
> out:
> return (unsigned char *)choice;
> }
> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index 3691451..075bb15 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -126,7 +126,7 @@ ENTRY(startup_32)
> /* Initialize Page tables to 0 */
> leal pgtable(%ebx), %edi
> xorl %eax, %eax
> - movl $((4096*6)/4), %ecx
> + movl $(BOOT_INIT_PGT_SIZE/4), %ecx
> rep stosl
>
> /* Build Level 4 */
> @@ -478,4 +478,4 @@ boot_stack_end:
> .section ".pgtable","a",@nobits
> .balign 4096
> pgtable:
> - .fill 6*4096, 1, 0
> + .fill BOOT_PGT_SIZE, 1, 0
> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> index dcf01c2..11736a6 100644
> --- a/arch/x86/boot/compressed/misc.h
> +++ b/arch/x86/boot/compressed/misc.h
> @@ -84,6 +84,17 @@ unsigned char *choose_kernel_location(unsigned char *input,
> }
> #endif
>
> +#ifdef CONFIG_X86_64
> +void fill_pagetable(unsigned long start, unsigned long size);
> +void switch_pagetable(void);
> +extern unsigned char _pgtable[];
> +#else
> +static inline void fill_pagetable(unsigned long start, unsigned long size)
> +{ }
> +static inline void switch_pagetable(void)
> +{ }
> +#endif
> +
> #ifdef CONFIG_EARLY_PRINTK
> /* early_serial_console.c */
> extern int early_serial_base;
> diff --git a/arch/x86/boot/compressed/misc_pgt.c b/arch/x86/boot/compressed/misc_pgt.c
> new file mode 100644
> index 0000000..954811e
> --- /dev/null
> +++ b/arch/x86/boot/compressed/misc_pgt.c
> @@ -0,0 +1,91 @@
> +#define __pa(x) ((unsigned long)(x))
> +#define __va(x) ((void *)((unsigned long)(x)))
> +
> +#include "misc.h"
> +
> +#include <asm/init.h>
> +#include <asm/pgtable.h>
> +
> +#include "../../mm/ident_map.c"
> +#include "../string.h"
> +
> +struct alloc_pgt_data {
> + unsigned char *pgt_buf;
> + unsigned long pgt_buf_size;
> + unsigned long pgt_buf_offset;
> +};
> +
> +static void *alloc_pgt_page(void *context)
> +{
> + struct alloc_pgt_data *d = (struct alloc_pgt_data *)context;
> + unsigned char *p = (unsigned char *)d->pgt_buf;
> +
> + if (d->pgt_buf_offset >= d->pgt_buf_size) {
> + debug_putstr("out of pgt_buf in misc.c\n");
This line probably isn't needed any more. Or, if it is, maybe it could
include more details from the context?
-Kees
> + return NULL;
> + }
> +
> + p += d->pgt_buf_offset;
> + d->pgt_buf_offset += PAGE_SIZE;
> +
> + return p;
> +}
> +
> +/*
> + * Use a normal definition of memset() from string.c. There are already
> + * included header files which expect a definition of memset() and by
> + * the time we define memset macro, it is too late.
> + */
> +#undef memset
> +
> +unsigned long __force_order;
> +static struct alloc_pgt_data pgt_data;
> +static struct x86_mapping_info mapping_info;
> +static pgd_t *level4p;
> +
> +void fill_pagetable(unsigned long start, unsigned long size)
> +{
> + unsigned long end = start + size;
> +
> + if (!level4p) {
> + pgt_data.pgt_buf_offset = 0;
> + mapping_info.alloc_pgt_page = alloc_pgt_page;
> + mapping_info.context = &pgt_data;
> + mapping_info.pmd_flag = __PAGE_KERNEL_LARGE_EXEC;
> +
> + /*
> + * come from startup_32 ?
> + * then cr3 is _pgtable, we can reuse it.
> + */
> + level4p = (pgd_t *)read_cr3();
> + if ((unsigned long)level4p == (unsigned long)_pgtable) {
> + pgt_data.pgt_buf = (unsigned char *)_pgtable +
> + BOOT_INIT_PGT_SIZE;
> + pgt_data.pgt_buf_size = BOOT_PGT_SIZE -
> + BOOT_INIT_PGT_SIZE;
> + memset((unsigned char *)pgt_data.pgt_buf, 0,
> + pgt_data.pgt_buf_size);
> + debug_putstr("boot via startup_32\n");
> + } else {
> + pgt_data.pgt_buf = (unsigned char *)_pgtable;
> + pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
> + memset((unsigned char *)pgt_data.pgt_buf, 0,
> + pgt_data.pgt_buf_size);
> + debug_putstr("boot via startup_64\n");
> + level4p = (pgd_t *)alloc_pgt_page(&pgt_data);
> + }
> + }
> +
> + /* align boundary to 2M */
> + start = round_down(start, PMD_SIZE);
> + end = round_up(end, PMD_SIZE);
> + if (start >= end)
> + return;
> +
> + kernel_ident_mapping_init(&mapping_info, level4p, start, end);
> +}
> +
> +void switch_pagetable(void)
> +{
> + write_cr3((unsigned long)level4p);
> +}
> diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
> index 6b8d6e8..52a9cbc 100644
> --- a/arch/x86/include/asm/boot.h
> +++ b/arch/x86/include/asm/boot.h
> @@ -32,7 +32,26 @@
> #endif /* !CONFIG_KERNEL_BZIP2 */
>
> #ifdef CONFIG_X86_64
> +
> #define BOOT_STACK_SIZE 0x4000
> +
> +#define BOOT_INIT_PGT_SIZE (6*4096)
> +#ifdef CONFIG_RANDOMIZE_BASE
> +/*
> + * 1 page for level4, 2 pages for first 2M.
> + * (2+2)*4 pages for kernel, param, cmd_line, random kernel
> + * if all cross 512G boundary.
> + * So total will be 19 pages.
> + */
> +#ifdef CONFIG_X86_VERBOSE_BOOTUP
> +#define BOOT_PGT_SIZE (19*4096)
> +#else
> +#define BOOT_PGT_SIZE (17*4096)
> +#endif
> +#else
> +#define BOOT_PGT_SIZE BOOT_INIT_PGT_SIZE
> +#endif
> +
> #else
> #define BOOT_STACK_SIZE 0x1000
> #endif
> --
> 2.5.0
>
--
Kees Cook
Chrome OS & Brillo Security
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