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    Subject[PATCH v3 2/3] KASLR: Handle memory limit specified by memmap and mem option
    Date
    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>
    Acked-by: Kees Cook <keescook@chromium.org>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: x86@kernel.org
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Yinghai Lu <yinghai@kernel.org>
    Cc: Borislav Petkov <bp@suse.de>
    ---
    arch/x86/boot/compressed/kaslr.c | 60 ++++++++++++++++++++++++++++++++--------
    1 file changed, 48 insertions(+), 12 deletions(-)

    diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
    index 53a06ec..e5eb0c3 100644
    --- a/arch/x86/boot/compressed/kaslr.c
    +++ b/arch/x86/boot/compressed/kaslr.c
    @@ -78,6 +78,10 @@ static bool memmap_too_large;
    extern unsigned long get_cmd_line_ptr(void);


    +/* 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,
    @@ -128,16 +132,22 @@ 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 '@':
    + /* memmap=nn@ss specifies usable region, should be skipped */
    + *size = 0;
    + 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;
    @@ -163,9 +173,14 @@ 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;
    @@ -189,6 +204,7 @@ static int handle_mem_memmap(void)
    size_t len = strlen((char *)args);
    char *tmp_cmdline;
    char *param, *val;
    + u64 mem_size;

    tmp_cmdline = malloc(COMMAND_LINE_SIZE);
    if (!tmp_cmdline )
    @@ -211,8 +227,20 @@ 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);
    @@ -449,7 +477,8 @@ 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)
    @@ -463,8 +492,15 @@ 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) {
    @@ -478,7 +514,7 @@ 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
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