Re: [PATCH v6] x86: fix kaslr and memmap collision

[Baoquan He]

On 01/10/17 at 10:56am, Dave Jiang 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@xxxxxxxxx>

Looks good to me, ack.

Acked-by: Baoquan He <bhe@xxxxxxxxxx>

> ---
>  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;
> +}
>