Re: [PATCH v3 1/3] KASLR: Parse all memmap entries in cmdline

[Kees Cook <keescook@chromium.org>]

On Wed, Apr 26, 2017 at 3:16 AM, Baoquan He <bhe@redhat.com> wrote:
> In commit:
>
>   f28442497b5c ("x86/boot: Fix KASLR and memmap= collision")
>
> ... the memmap= option is parsed so that KASLR can avoid those reserved
> regions. It uses cmdline_find_option() to get the value if memmap=
> is specified, however the problem is that cmdline_find_option() can only
> find the last entry if multiple memmap entries are provided. This
> is not correct.
>
> In this patch, the whole cmdline will be scanned to search each
> memmap, all of them will be parsed and handled.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: x86@kernel.org
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Yinghai Lu <yinghai@kernel.org>
> Cc: Borislav Petkov <bp@suse.de>
> ---
>  arch/x86/boot/compressed/cmdline.c |   2 +-
>  arch/x86/boot/compressed/kaslr.c   | 125 +++++++++++++++++++++----------------
>  arch/x86/boot/string.c             |   8 +++
>  3 files changed, 80 insertions(+), 55 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/cmdline.c b/arch/x86/boot/compressed/cmdline.c
> index 73ccf63..9dc1ce6 100644
> --- a/arch/x86/boot/compressed/cmdline.c
> +++ b/arch/x86/boot/compressed/cmdline.c
> @@ -13,7 +13,7 @@ static inline char rdfs8(addr_t addr)
>         return *((char *)(fs + addr));
>  }
>  #include "../cmdline.c"
> -static unsigned long get_cmd_line_ptr(void)
> +unsigned long get_cmd_line_ptr(void)
>  {
>         unsigned long cmd_line_ptr = boot_params->hdr.cmd_line_ptr;
>
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 6d9a546..53a06ec 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -9,14 +9,28 @@
>   * contain the entire properly aligned running kernel image.
>   *
>   */
> +
> +/*
> + * linux/ctype.h is expected, while conflicts with boot/ctype.h
> + * which is useless here. Do not include it.
> + */
> +#define BOOT_CTYPE_H

Which include includes this?

> +
> +/*
> + * Exporting symbol in boot stage is meaningless, and will trigger
> + * compiling error in some cases. Disable it here.
> + */
> +#define _LINUX_EXPORT_H
> +#define EXPORT_SYMBOL(sym)

And this?

> +
>  #include "misc.h"
>  #include "error.h"
> -#include "../boot.h"
>
>  #include <generated/compile.h>
>  #include <linux/module.h>
>  #include <linux/uts.h>
>  #include <linux/utsname.h>
> +#include <linux/ctype.h>

Why is misc.h's ctype insufficient?

>  #include <generated/utsrelease.h>
>
>  /* Simplified build-specific string for starting entropy. */
> @@ -61,6 +75,8 @@ struct mem_vector {
>  #define MAX_MEMMAP_REGIONS     4
>
>  static bool memmap_too_large;
> +extern unsigned long get_cmd_line_ptr(void);

Can we avoid an extern in .c? Seems like this should be defined in
misc.h or similar?

> +
>
>  enum mem_avoid_index {
>         MEM_AVOID_ZO_RANGE = 0,
> @@ -85,49 +101,14 @@ static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
>         return true;
>  }
>
> -/**
> - *     _memparse - Parse a string with mem suffixes into a number
> - *     @ptr: Where parse begins
> - *     @retptr: (output) Optional pointer to next char after parse completes
> - *
> - *     Parses a string into a number.  The number stored at @ptr is
> - *     potentially suffixed with K, M, G, T, P, E.
> - */
> -static unsigned long long _memparse(const char *ptr, char **retptr)
> +char *skip_spaces(const char *str)
>  {
> -       char *endptr;   /* Local pointer to end of parsed string */
> -
> -       unsigned long long ret = simple_strtoull(ptr, &endptr, 0);
> -
> -       switch (*endptr) {
> -       case 'E':
> -       case 'e':
> -               ret <<= 10;
> -       case 'P':
> -       case 'p':
> -               ret <<= 10;
> -       case 'T':
> -       case 't':
> -               ret <<= 10;
> -       case 'G':
> -       case 'g':
> -               ret <<= 10;
> -       case 'M':
> -       case 'm':
> -               ret <<= 10;
> -       case 'K':
> -       case 'k':
> -               ret <<= 10;
> -               endptr++;
> -       default:
> -               break;
> -       }
> -
> -       if (retptr)
> -               *retptr = endptr;
> -
> -       return ret;
> +       while (isspace(*str))
> +               ++str;
> +       return (char *)str;
>  }
> +#include "../../../../lib/ctype.c"
> +#include "../../../../lib/cmdline.c"
>
>  static int
>  parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
> @@ -142,7 +123,7 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
>                 return -EINVAL;
>
>         oldp = p;
> -       *size = _memparse(p, &p);
> +       *size = memparse(p, &p);
>         if (p == oldp)
>                 return -EINVAL;
>
> @@ -155,27 +136,21 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
>         case '#':
>         case '$':
>         case '!':
> -               *start = _memparse(p + 1, &p);
> +               *start = memparse(p + 1, &p);
>                 return 0;
>         }
>
>         return -EINVAL;
>  }
>
> -static void mem_avoid_memmap(void)
> +static void mem_avoid_memmap(char *str)
>  {
> -       char arg[128];
> +       static int i;
>         int rc;
> -       int i;
> -       char *str;
>
> -       /* See if we have any memmap areas */
> -       rc = cmdline_find_option("memmap", arg, sizeof(arg));
> -       if (rc <= 0)
> +       if (i >= MAX_MEMMAP_REGIONS)
>                 return;
>
> -       i = 0;
> -       str = arg;
>         while (str && (i < MAX_MEMMAP_REGIONS)) {
>                 int rc;
>                 unsigned long long start, size;
> @@ -202,6 +177,48 @@ static void mem_avoid_memmap(void)
>                 memmap_too_large = true;
>  }
>
> +
> +/* Macros used by the included decompressor code below. */
> +#define STATIC
> +#include <linux/decompress/mm.h>

Can this be moved to the top of the file? (Also, I wonder if maybe it
should be moved into misc.h?)

> +
> +#define COMMAND_LINE_SIZE 256
> +static int handle_mem_memmap(void)
> +{
> +       char *args = (char *)get_cmd_line_ptr();
> +       size_t len = strlen((char *)args);
> +       char *tmp_cmdline;
> +       char *param, *val;
> +

Here to optimize for the common case, please do something like:

if (!strstr("memmap=", args))
    return 0;

> +       tmp_cmdline = malloc(COMMAND_LINE_SIZE);

Instead of COMMAND_LINE_SIZE hard-limit, please attempt a malloc of
len + 1. Then you don't have to play games with len adjustments,
truncation, etc.

> +       if (!tmp_cmdline )
> +               error("Failed to allocate space for tmp_cmdline");
> +
> +       len = (len >= COMMAND_LINE_SIZE) ? COMMAND_LINE_SIZE - 1 : len;
> +       memcpy(tmp_cmdline, args, len);
> +       tmp_cmdline[len] = 0;
> +       args = tmp_cmdline;
> +
> +       /* Chew leading spaces */
> +       args = skip_spaces(args);
> +
> +       while (*args) {
> +               args = next_arg(args, &param, &val);
> +               /* Stop at -- */
> +               if (!val && strcmp(param, "--") == 0) {
> +                       warn("Only '--' specified in cmdline");
> +                       free(tmp_cmdline);
> +                       return -1;
> +               }
> +
> +               if (!strcmp(param, "memmap"))
> +                       mem_avoid_memmap(val);
> +       }
> +
> +       free(tmp_cmdline);
> +       return 0;
> +}
> +
>  /*
>   * In theory, KASLR can put the kernel anywhere in the range of [16M, 64T).
>   * The mem_avoid array is used to store the ranges that need to be avoided
> @@ -323,7 +340,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
>         /* We don't need to set a mapping for setup_data. */
>
>         /* Mark the memmap regions we need to avoid */
> -       mem_avoid_memmap();
> +       handle_mem_memmap();

The first "mem" in this name seems redundant.

>
>  #ifdef CONFIG_X86_VERBOSE_BOOTUP
>         /* Make sure video RAM can be used. */
> diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
> index 5457b02..630e366 100644
> --- a/arch/x86/boot/string.c
> +++ b/arch/x86/boot/string.c
> @@ -122,6 +122,14 @@ unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int bas
>         return result;
>  }
>
> +long simple_strtol(const char *cp, char **endp, unsigned int base)
> +{
> +       if (*cp == '-')
> +               return -simple_strtoull(cp + 1, endp, base);
> +
> +       return simple_strtoull(cp, endp, base);
> +}
> +
>  /**
>   * strlen - Find the length of a string
>   * @s: The string to be sized
> --
> 2.5.5
>

Looks like it's making progress, thanks!

-Kees

-- 
Kees Cook
Pixel Security