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SubjectRe: [PATCH v4 2/3] KASLR: Handle memory limit specified by memmap and mem option
On Mon, May 8, 2017 at 10:57 PM, Baoquan He <bhe@redhat.com> wrote:
> Option mem= will limit the max address a system can use and any memory
> region above the limit will be removed.
>
> Furthermore, memmap=nn[KMG] which has no offset specified has the same
> behaviour as mem=.
>
> KASLR needs to consider this when choosing the random position for
> decompressing the kernel.
>
> This patch implements that.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
> arch/x86/boot/compressed/kaslr.c | 69 +++++++++++++++++++++++++++++-----------
> 1 file changed, 51 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 106e13b..0637e85 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -88,6 +88,10 @@ struct mem_vector {
> static bool memmap_too_large;
>
>
> +/* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
> +unsigned long long mem_limit = ULLONG_MAX;
> +
> +
> enum mem_avoid_index {
> MEM_AVOID_ZO_RANGE = 0,
> MEM_AVOID_INITRD,
> @@ -138,16 +142,24 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
> 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;
> + case '@': /* Fall through: */
> + /*
> + * memmap=nn@ss specifies usable region, should be skipped
> + */
> + *size = 0;

The "fall through" comment should go here (where the break is "missing").

> + default:
> + /*
> + * If w/o offset, only size specified, memmap=nn[KMG] has the
> + * same behaviour as mem=nn[KMG]. It limits the max address
> + * system can use. Region above the limit should be avoided.
> + */
> + *start = 0;
> + return 0;
> }
>
> return -EINVAL;
> @@ -173,9 +185,14 @@ static void mem_avoid_memmap(char *str)
> if (rc < 0)
> break;
> str = k;
> - /* A usable region that should not be skipped */
> - if (size == 0)
> +
> + if (start == 0) {
> + /* Store the specified memory limit if size > 0 */
> + if (size > 0)
> + mem_limit = size;
> +
> continue;
> + }
>
> mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
> mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
> @@ -187,19 +204,15 @@ static void mem_avoid_memmap(char *str)
> memmap_too_large = true;
> }
>
> -
> -/*
> - * handle_mem_memmap will also cover 'mem=' issue in next patch. Will remove
> - * this note later.
> - */
> static int handle_mem_memmap(void)
> {
> char *args = (char *)get_cmd_line_ptr();
> size_t len = strlen((char *)args);
> char *tmp_cmdline;
> char *param, *val;
> + u64 mem_size;
>
> - if (!strstr(args, "memmap="))
> + if (!strstr(args, "memmap=") && !strstr(args, "mem="))
> return 0;
>
> tmp_cmdline = malloc(len + 1);
> @@ -222,8 +235,20 @@ static int handle_mem_memmap(void)
> return -1;
> }
>
> - if (!strcmp(param, "memmap"))
> + if (!strcmp(param, "memmap")) {
> mem_avoid_memmap(val);
> + } else if (!strcmp(param, "mem")) {
> + char *p = val;
> +
> + if (!strcmp(p, "nopentium"))
> + continue;
> + mem_size = memparse(p, &p);
> + if (mem_size == 0) {
> + free(tmp_cmdline);
> + return -EINVAL;
> + }
> + mem_limit = mem_size;
> + }
> }
>
> free(tmp_cmdline);
> @@ -460,7 +485,8 @@ static void process_e820_entry(struct boot_e820_entry *entry,
> {
> struct mem_vector region, overlap;
> struct slot_area slot_area;
> - unsigned long start_orig;
> + unsigned long start_orig, end;
> + struct boot_e820_entry cur_entry;
>
> /* Skip non-RAM entries. */
> if (entry->type != E820_TYPE_RAM)
> @@ -474,8 +500,15 @@ static void process_e820_entry(struct boot_e820_entry *entry,
> if (entry->addr + entry->size < minimum)
> return;
>
> - region.start = entry->addr;
> - region.size = entry->size;
> + /* Ignore entries above memory limit */
> + end = min(entry->size + entry->addr, mem_limit);
> + if (entry->addr >= end)
> + return;
> + cur_entry.addr = entry->addr;
> + cur_entry.size = end - entry->addr;
> +
> + region.start = cur_entry.addr;
> + region.size = cur_entry.size;
>
> /* Give up if slot area array is full. */
> while (slot_area_index < MAX_SLOT_AREA) {
> @@ -489,7 +522,7 @@ static void process_e820_entry(struct boot_e820_entry *entry,
> region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
>
> /* Did we raise the address above this e820 region? */
> - if (region.start > entry->addr + entry->size)
> + if (region.start > cur_entry.addr + cur_entry.size)
> return;
>
> /* Reduce size by any delta from the original address. */
> --
> 2.5.5
>

Otherwise looks fine to me!

-Kees

--
Kees Cook
Pixel Security

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