Re: [PATCH v3 10/19] x86, 64bit: Set ident_mapping for kaslr

[Baoquan He]

On 03/07/16 at 03:34pm, Kees Cook wrote:
> On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <bhe@xxxxxxxxxx> wrote:
> > From: Yinghai Lu <yinghai@xxxxxxxxxx>
> > 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.

OK, will change it as follows:

	fill_pagetable(mem_avoid[0].start, mem_avoid[0].size);
> 
> >
> >         /* 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