On Tue, Nov 22, 2016 at 9:26 AM, Dan Williams <dan.j.willi...@intel.com> wrote:
> [ replying for Dave since he's offline today and tomorrow ]
>
> On Tue, Nov 22, 2016 at 12:47 AM, Ingo Molnar <mi...@kernel.org> wrote:
>>
>> * Dave Jiang <dave.ji...@intel.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 commandline.
>>
>> memmap= parameters are often used as a list.
>>
>>> [...] This results in the kernel sometimes being put in the middle of the
>>> user
>>> memmap. [...]
>>
>> What does this mean? If memmap= is used to re-define the memory map then the
>> kernel getting in the middle of a RAM area is what we want, isn't it? What we
>> don't want is for the kernel to get into reserved areas, right?
>
> Right, this is about teaching kaslr to not land the kernel in newly
> defined reserved regions that were not marked reserved in the initial
> e820 map from platform firmware.
>
>>> [...] Check has been added in the kaslr in order to avoid the region marked
>>> by
>>> memmap.
>>
>> What does this mean?
>
> Is this clearer? "Update the set of 'mem_avoid' entries to exclude
> 'memmap=' defined reserved regions from the set of valid address range
> to land the kernel image."
>
>>
>>> Signed-off-by: Dave Jiang <dave.ji...@intel.com>
>>> ---
>>> arch/x86/boot/boot.h | 2 ++
>>> arch/x86/boot/compressed/kaslr.c | 45
>>> ++++++++++++++++++++++++++++++++++++++
>>> arch/x86/boot/string.c | 25 +++++++++++++++++++++
>>> 3 files changed, 72 insertions(+)
>>>
>>> diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
>>> index e5612f3..0d5fe5b 100644
>>> --- a/arch/x86/boot/boot.h
>>> +++ b/arch/x86/boot/boot.h
>>> @@ -332,6 +332,8 @@ 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);
>>>
>>> /* tty.c */
>>> diff --git a/arch/x86/boot/compressed/kaslr.c
>>> b/arch/x86/boot/compressed/kaslr.c
>>> index a66854d..6fb8f1ec 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>
>>> @@ -61,6 +62,7 @@ enum mem_avoid_index {
>>> MEM_AVOID_INITRD,
>>> MEM_AVOID_CMDLINE,
>>> MEM_AVOID_BOOTPARAMS,
>>> + MEM_AVOID_MEMMAP,
>>> MEM_AVOID_MAX,
>>> };
>>>
>>> @@ -77,6 +79,37 @@ 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;
>>> +}
>>> +
>>> /*
>>> * 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
>>> @@ -158,6 +191,8 @@ static void mem_avoid_init(unsigned long input,
>>> unsigned long input_size,
>>> u64 initrd_start, initrd_size;
>>> u64 cmd_line, cmd_line_size;
>>> char *ptr;
>>> + char arg[38];
>>
>> Where does the magic '38' come from?
>>
>>> + unsigned long long memmap_start, memmap_size;
>>>
>>> /*
>>> * Avoid the region that is unsafe to overlap during
>>> @@ -195,6 +230,16 @@ static void mem_avoid_init(unsigned long input,
>>> unsigned long input_size,
>>> add_identity_map(mem_avoid[MEM_AVOID_BOOTPARAMS].start,
>>> mem_avoid[MEM_AVOID_BOOTPARAMS].size);
>>>
>>> + /* see if we have any memmap areas */
>>> + if (cmdline_find_option("memmap", arg, sizeof(arg)) > 0) {
>>> + int rc = parse_memmap(arg, &memmap_start, &memmap_size);
>>> +
>>> + if (!rc) {
>>> + mem_avoid[MEM_AVOID_MEMMAP].start = memmap_start;
>>> + mem_avoid[MEM_AVOID_MEMMAP].size = memmap_size;
>>> + }
>>> + }
>>> +
>>
>> This only handles a single (first) memmap argument, is that sufficient?
>
> No, you're right, we need to handle multiple ranges. Since the
> mem_avoid array is statically allocated perhaps we can handle up to 4
> memmap= entries, but past that point disable kaslr for that boot?
Yeah, that seems fine to me. I assume it's rare to have 4?
-Kees
--
Kees Cook
Nexus Security
