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Message-ID: <CAGXu5jJpuRae05_qPr1oij4-7yEykJ+WN4WX9E2tBKxdD9g-ug@mail.gmail.com>
Date: Tue, 10 Jan 2017 11:02:35 -0800
From: Kees Cook <keescook@...omium.org>
To: Dave Jiang <dave.jiang@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Baoquan He <bhe@...hat.com>,
linux-nvdimm@...ts.01.org, "x86@...nel.org" <x86@...nel.org>,
Dave Chinner <david@...morbit.com>,
LKML <linux-kernel@...r.kernel.org>,
Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v6] x86: fix kaslr and memmap collision
On Tue, Jan 10, 2017 at 9:56 AM, Dave Jiang <dave.jiang@...el.com> wrote:
> CONFIG_RANDOMIZE_BASE relocates the kernel to a random base address.
> However it does not take into account the memmap= parameter passed in from
> the kernel cmdline. This results in the kernel sometimes being put in
> the middle of memmap. Teaching kaslr to not insert the kernel in
> memmap defined regions. We will support up to 4 memmap regions. Any
> additional regions will cause kaslr to disable. The mem_avoid set has
> been augmented to add up to 4 unusable regions of memmaps provided by the
> user to exclude those regions from the set of valid address range to insert
> the uncompressed kernel image. The nn@ss ranges will be skipped by the
> mem_avoid set since it indicates memory useable.
>
> Signed-off-by: Dave Jiang <dave.jiang@...el.com>
Thanks for the updates!
Acked-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> arch/x86/boot/boot.h | 3 +
> arch/x86/boot/compressed/kaslr.c | 132 ++++++++++++++++++++++++++++++++++++++
> arch/x86/boot/string.c | 38 +++++++++++
> 3 files changed, 172 insertions(+), 1 deletion(-)
>
> v2:
> Addressing comments from Ingo.
> - Handle entire list of memmaps
> v3:
> Fix 32bit build issue
> v4:
> Addressing comments from Baoquan
> - Not exclude nn@ss ranges
> v5:
> Addressing additional comments from Baoquan
> - Update commit header and various coding style changes
> v6:
> Address comments from Kees
> - Only fail for physical address randomization
>
> diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
> index e5612f3..59c2075 100644
> --- a/arch/x86/boot/boot.h
> +++ b/arch/x86/boot/boot.h
> @@ -332,7 +332,10 @@ int strncmp(const char *cs, const char *ct, size_t count);
> size_t strnlen(const char *s, size_t maxlen);
> unsigned int atou(const char *s);
> unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base);
> +unsigned long simple_strtoul(const char *cp, char **endp, unsigned int base);
> +long simple_strtol(const char *cp, char **endp, unsigned int base);
> size_t strlen(const char *s);
> +char *strchr(const char *s, int c);
>
> /* tty.c */
> void puts(const char *);
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index a66854d..e919b70 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -11,6 +11,7 @@
> */
> #include "misc.h"
> #include "error.h"
> +#include "../boot.h"
>
> #include <generated/compile.h>
> #include <linux/module.h>
> @@ -56,11 +57,18 @@ struct mem_vector {
> unsigned long size;
> };
>
> +/* only supporting at most 4 unusable memmap regions with kaslr */
> +#define MAX_MEMMAP_REGIONS 4
> +
> +static bool memmap_too_large;
> +
> enum mem_avoid_index {
> MEM_AVOID_ZO_RANGE = 0,
> MEM_AVOID_INITRD,
> MEM_AVOID_CMDLINE,
> MEM_AVOID_BOOTPARAMS,
> + MEM_AVOID_MEMMAP_BEGIN,
> + MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
> MEM_AVOID_MAX,
> };
>
> @@ -77,6 +85,119 @@ 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 *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;
> +}
> +
> +static int
> +parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
> +{
> + char *oldp;
> +
> + if (!p)
> + return -EINVAL;
> +
> + /* we don't care about this option here */
> + if (!strncmp(p, "exactmap", 8))
> + return -EINVAL;
> +
> + oldp = p;
> + *size = _memparse(p, &p);
> + if (p == oldp)
> + return -EINVAL;
> +
> + switch (*p) {
> + case '@':
> + /* skip this region, usable */
> + *start = 0;
> + *size = 0;
> + return 0;
> + case '#':
> + case '$':
> + case '!':
> + *start = _memparse(p + 1, &p);
> + return 0;
> + }
> +
> + return -EINVAL;
> +}
> +
> +static void mem_avoid_memmap(void)
> +{
> + char arg[128];
> + int rc = 0;
> +
> + /* see if we have any memmap areas */
> + if (cmdline_find_option("memmap", arg, sizeof(arg)) > 0) {
> + int i = 0;
> + char *str = arg;
> +
> + while (str && (i < MAX_MEMMAP_REGIONS)) {
> + unsigned long long start, size;
> + char *k = strchr(str, ',');
> +
> + if (k)
> + *k++ = 0;
> +
> + rc = parse_memmap(str, &start, &size);
> + if (rc < 0)
> + break;
> + str = k;
> + /* a usable region that should not be skipped */
> + if (size == 0)
> + continue;
> +
> + mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
> + mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
> + i++;
> + }
> +
> + /* more than 4 memmaps, fail kaslr */
> + if ((i >= MAX_MEMMAP_REGIONS) && str)
> + memmap_too_large = true;
> + }
> +}
> +
> /*
> * 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
> @@ -197,6 +318,9 @@ 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();
> +
> #ifdef CONFIG_X86_VERBOSE_BOOTUP
> /* Make sure video RAM can be used. */
> add_identity_map(0, PMD_SIZE);
> @@ -379,6 +503,12 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
> int i;
> unsigned long addr;
>
> + /* Check if we had too many memmaps. */
> + if (memmap_too_large) {
> + debug_putstr("Aborted e820 scan (more than 4 memmap= args)!\n");
> + return 0;
> + }
> +
> /* Make sure minimum is aligned. */
> minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
>
> @@ -456,7 +586,7 @@ void choose_random_location(unsigned long input,
> /* Walk e820 and find a random address. */
> random_addr = find_random_phys_addr(min_addr, output_size);
> if (!random_addr) {
> - warn("KASLR disabled: could not find suitable E820 region!");
> + warn("Physical KASLR disabled: no suitable memory region!");
> } else {
> /* Update the new physical address location. */
> if (*output != random_addr) {
> diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
> index cc3bd58..0464aaa 100644
> --- a/arch/x86/boot/string.c
> +++ b/arch/x86/boot/string.c
> @@ -122,6 +122,31 @@ unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int bas
> }
>
> /**
> + * simple_strtoul - convert a string to an unsigned long
> + * @cp: The start of the string
> + * @endp: A pointer to the end of the parsed string will be placed here
> + * @base: The number base to use
> + */
> +unsigned long simple_strtoul(const char *cp, char **endp, unsigned int base)
> +{
> + return simple_strtoull(cp, endp, base);
> +}
> +
> +/**
> + * simple_strtol - convert a string to a signed long
> + * @cp: The start of the string
> + * @endp: A pointer to the end of the parsed string will be placed here
> + * @base: The number base to use
> + */
> +long simple_strtol(const char *cp, char **endp, unsigned int base)
> +{
> + if (*cp == '-')
> + return -simple_strtoul(cp + 1, endp, base);
> +
> + return simple_strtoul(cp, endp, base);
> +}
> +
> +/**
> * strlen - Find the length of a string
> * @s: The string to be sized
> */
> @@ -155,3 +180,16 @@ char *strstr(const char *s1, const char *s2)
> }
> return NULL;
> }
> +
> +/**
> + * strchr - Find the first occurrence of the character c in the string s.
> + * @s: the string to be searched
> + * @c: the character to search for
> + */
> +char *strchr(const char *s, int c)
> +{
> + while (*s != (char)c)
> + if (*s++ == '\0')
> + return NULL;
> + return (char *)s;
> +}
>
--
Kees Cook
Nexus Security
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