Re: [PATCH v2] x86: fix kaslr and memmap collision

[Dave Jiang]

On 11/29/2016 12:26 PM, 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 the user 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 regions of memmaps provided by the user
> to exclude those regions from the set of valid address range to insert
> the uncompressed kernel image.
> 
> Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>

Peter, Ingo, or Thomas,
Is this patch ok? Will someone be picking it up for 4.10? Thanks.

> ---
>  arch/x86/boot/boot.h             |    3 +
>  arch/x86/boot/compressed/kaslr.c |   82 ++++++++++++++++++++++++++++++++++++++
>  arch/x86/boot/string.c           |   38 ++++++++++++++++++
>  3 files changed, 123 insertions(+)
> 
> 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..915509f 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>
> @@ -61,9 +62,16 @@ enum mem_avoid_index {
>  	MEM_AVOID_INITRD,
>  	MEM_AVOID_CMDLINE,
>  	MEM_AVOID_BOOTPARAMS,
> +	MEM_AVOID_MEMMAP1,
> +	MEM_AVOID_MEMMAP2,
> +	MEM_AVOID_MEMMAP3,
> +	MEM_AVOID_MEMMAP4,
>  	MEM_AVOID_MAX,
>  };
>  
> +/* only supporting at most 4 memmap regions with kaslr */
> +#define MAX_MEMMAP_REGIONS	4
> +
>  static struct mem_vector mem_avoid[MEM_AVOID_MAX];
>  
>  static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
> @@ -77,6 +85,72 @@ static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
>  	return true;
>  }
>  
> +#include "../../../../lib/cmdline.c"
> +
> +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 '@':
> +	case '#':
> +	case '$':
> +	case '!':
> +		*start = memparse(p + 1, &p);
> +		return 0;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int 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;
> +
> +			mem_avoid[MEM_AVOID_MEMMAP1 + i].start = start;
> +			mem_avoid[MEM_AVOID_MEMMAP1 + i].size = size;
> +			i++;
> +		}
> +
> +		/* more than 4 memmaps, fail kaslr */
> +		if ((i >= MAX_MEMMAP_REGIONS) && str)
> +			rc = -EINVAL;
> +	}
> +
> +	return rc;
> +}
> +
>  /*
>   * 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
> @@ -429,6 +503,7 @@ void choose_random_location(unsigned long input,
>  			    unsigned long *virt_addr)
>  {
>  	unsigned long random_addr, min_addr;
> +	int rc;
>  
>  	/* By default, keep output position unchanged. */
>  	*virt_addr = *output;
> @@ -438,6 +513,13 @@ void choose_random_location(unsigned long input,
>  		return;
>  	}
>  
> +	/* Mark the memmap regions we need to avoid */
> +	rc = mem_avoid_memmap();
> +	if (rc < 0) {
> +		warn("KASLR disabled: memmap exceeds limit of 4, giving up.");
> +		return;
> +	}
> +
>  	boot_params->hdr.loadflags |= KASLR_FLAG;
>  
>  	/* Prepare to add new identity pagetables on demand. */
> 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;
> +}
>