Messages in this thread | | | Date | Thu, 5 Jan 2017 17:21:31 +0800 | From | Baoquan He <> | Subject | Re: [PATCH v5] x86: fix kaslr and memmap collision |
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On 01/04/17 at 11:29am, 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@intel.com> > --- > > 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 > > 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..036b514 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 +57,16 @@ struct mem_vector { > unsigned long size; > }; > > +/* only supporting at most 4 unusable memmap regions with kaslr */ > +#define MAX_MEMMAP_REGIONS 4 > + > 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 +83,121 @@ 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 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; > + /* 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) > + 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 > @@ -438,6 +559,12 @@ void choose_random_location(unsigned long input, > return; > } > > + /* Mark the memmap regions we need to avoid */ > + if (mem_avoid_memmap()) { > + warn("KASLR disabled: memmap exceeds limit of 4, giving up."); > + return; > + }
theoretically, mem_avoid_memmap is doing the mem_avoid initialization job, should be called inside mem_avoid_init(). The reason you put it here is you want to make it cancel kaslr, both physical and virtual address randomization, right?
In choose_random_location(), the physical and virtual random are done separately. You can see that later when find_random_phys_addr failed to find a suitable random slot, it just prints a warning, virtual randomization is still be done with calling find_random_virt_addr(). Avoiding memmap reserved region should be physical ram issue, should we stop the kernel virtual address randomization either?
Kees, what do you think about this?
> + > 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; > +} >
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