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    SubjectRe: [PATCH v3 1/4] kaslr: add immovable_mem=nn[KMG]@ss[KMG] to specify extracting memory
    On Tue, Dec 5, 2017 at 12:51 AM, Chao Fan <fanc.fnst@cn.fujitsu.com> wrote:
    > In current code, kaslr may choose the memory region in movable
    > nodes to extract kernel, which will make the nodes can't be hot-removed.
    > To solve it, we can specify the memory region in immovable node.
    > Create immovable_mem to store the regions in immovable_mem, where should
    > be chosen by kaslr.
    >
    > Multiple regions can be specified, comma delimited.
    > Considering the usage of memory, only support for 4 regions.
    > 4 regions contains 2 nodes at least, enough for kernel to extract.
    >
    > Also change the "handle_mem_memmap" to "handle_mem_filter", since
    > it will not only handle memmap parameter now.

    I would put all immovable region functions and variables behind
    #ifdefs. e.g. parse_immovable_mem() is unused without
    CONFIG_MEMORY_HOTPLUG. I also wonder if it might be possible to reuse
    some of the parsing code and just pass in which array you're updating
    (i.e. memmap array vs immovable array).

    -Kees

    >
    > Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
    > ---
    > arch/x86/boot/compressed/kaslr.c | 80 ++++++++++++++++++++++++++++++++++++++--
    > 1 file changed, 77 insertions(+), 3 deletions(-)
    >
    > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
    > index a63fbc25ce84..0bbbaf5f6370 100644
    > --- a/arch/x86/boot/compressed/kaslr.c
    > +++ b/arch/x86/boot/compressed/kaslr.c
    > @@ -108,6 +108,15 @@ enum mem_avoid_index {
    >
    > static struct mem_vector mem_avoid[MEM_AVOID_MAX];
    >
    > +/* Only supporting at most 4 immovable memory regions with kaslr */
    > +#define MAX_IMMOVABLE_MEM 4
    > +
    > +/* Store the memory regions in immovable node */
    > +static struct mem_vector immovable_mem[MAX_IMMOVABLE_MEM];
    > +
    > +/* The immovable regions user specify, not more than 4 */
    > +static int num_immovable_region;
    > +
    > static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
    > {
    > /* Item one is entirely before item two. */
    > @@ -168,6 +177,38 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
    > return -EINVAL;
    > }
    >
    > +static int parse_immovable_mem(char *p,
    > + unsigned long long *start,
    > + unsigned long long *size)
    > +{
    > + char *oldp;
    > +
    > + if (!p)
    > + return -EINVAL;
    > +
    > + oldp = p;
    > + *size = memparse(p, &p);
    > + if (p == oldp)
    > + return -EINVAL;
    > +
    > + /* We support nn[KMG]@ss[KMG] and nn[KMG]. */
    > + switch (*p) {
    > + case '@':
    > + *start = memparse(p + 1, &p);
    > + return 0;
    > + default:
    > + /*
    > + * If w/o offset, only size specified, immovable_mem=nn[KMG]
    > + * has the same behaviour as immovable_mem=nn[KMG]@0. It means
    > + * the region starts from 0.
    > + */
    > + *start = 0;
    > + return 0;
    > + }
    > +
    > + return -EINVAL;
    > +}
    > +
    > static void mem_avoid_memmap(char *str)
    > {
    > static int i;
    > @@ -207,7 +248,37 @@ static void mem_avoid_memmap(char *str)
    > memmap_too_large = true;
    > }
    >
    > -static int handle_mem_memmap(void)
    > +#ifdef CONFIG_MEMORY_HOTPLUG
    > +static void parse_immovable_mem_regions(char *str)
    > +{
    > + static int i;
    > +
    > + while (str && (i < MAX_IMMOVABLE_MEM)) {
    > + int rc;
    > + unsigned long long start, size;
    > + char *k = strchr(str, ',');
    > +
    > + if (k)
    > + *k++ = 0;
    > +
    > + rc = parse_immovable_mem(str, &start, &size);
    > + if (rc < 0)
    > + break;
    > + str = k;
    > +
    > + immovable_mem[i].start = start;
    > + immovable_mem[i].size = size;
    > + i++;
    > + }
    > + num_immovable_region = i;
    > +}
    > +#else
    > +static inline void parse_immovable_mem_regions(char *str)
    > +{
    > +}
    > +#endif
    > +
    > +static int handle_mem_filter(void)
    > {
    > char *args = (char *)get_cmd_line_ptr();
    > size_t len = strlen((char *)args);
    > @@ -215,7 +286,8 @@ static int handle_mem_memmap(void)
    > char *param, *val;
    > u64 mem_size;
    >
    > - if (!strstr(args, "memmap=") && !strstr(args, "mem="))
    > + if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
    > + !strstr(args, "immovable_mem="))
    > return 0;
    >
    > tmp_cmdline = malloc(len + 1);
    > @@ -240,6 +312,8 @@ static int handle_mem_memmap(void)
    >
    > if (!strcmp(param, "memmap")) {
    > mem_avoid_memmap(val);
    > + } else if (!strcmp(param, "immovable_mem")) {
    > + parse_immovable_mem_regions(val);
    > } else if (!strcmp(param, "mem")) {
    > char *p = val;
    >
    > @@ -379,7 +453,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
    > /* We don't need to set a mapping for setup_data. */
    >
    > /* Mark the memmap regions we need to avoid */
    > - handle_mem_memmap();
    > + handle_mem_filter();
    >
    > #ifdef CONFIG_X86_VERBOSE_BOOTUP
    > /* Make sure video RAM can be used. */
    > --
    > 2.14.3
    >
    >
    >



    --
    Kees Cook
    Pixel Security

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