Messages in this thread | | | Date | Wed, 19 Apr 2017 07:12:40 +0800 | From | Baoquan He <> | Subject | Re: [PATCH 3/4] KASLR: Handle memory limit specified by memmap and mem option |
| |
On 04/18/17 at 01:36pm, Kees Cook wrote: > On Mon, Apr 17, 2017 at 6:34 AM, Baoquan He <bhe@redhat.com> wrote: > > Option mem= will limit the max address system can use. Any memory > > region above the limit will be removed. And memmap=nn[KMG] which > > has no offset specified has the same behaviour as mem=. KASLR need > > consider this when choose the random position for decompressing > > kernel. Do it in this patch. > > > > Signed-off-by: Baoquan He <bhe@redhat.com> > > 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 | 53 +++++++++++++++++++++++++++++++--------- > > 1 file changed, 42 insertions(+), 11 deletions(-) > > > > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c > > index 36ab429..5361abd 100644 > > --- a/arch/x86/boot/compressed/kaslr.c > > +++ b/arch/x86/boot/compressed/kaslr.c > > @@ -67,6 +67,10 @@ int mem_avoid_memmap_index; > > 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; > > I would either make this 0 or ULLONG_MAX - 1 (see below).
I prefer "ULLONG_MAX-1". Please see reason below
> > > + > > + > > enum mem_avoid_index { > > MEM_AVOID_ZO_RANGE = 0, > > MEM_AVOID_INITRD, > > @@ -117,15 +121,18 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size) > > return -EINVAL; > > > > switch (*p) { > > - case '@': > > - /* Skip this region, usable */ > > - *size = 0; > > - *start = 0; > > case '#': > > case '$': > > case '!': > > *start = memparse(p + 1, &p); > > return 0; > > + case '@': > > + /* Skip this region, usable */ > > + *size = 0; > > Now it looks like we're intentionally falling through. A comment > should be included to indicate it.
Yes, as I replied in patch 2/4, it's intended. Will add comment to indicate.
> > > + default: > > + /* Avoid the region which is above the amount limit */ > > + *start = 0; > > + return 0; > > } > > > > return -EINVAL; > > @@ -151,9 +158,14 @@ 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; > > @@ -173,6 +185,7 @@ static int handle_mem_memmap(void) > > char tmp_cmdline[COMMAND_LINE_SIZE]; > > size_t len = strlen((char *)args); > > char *param, *val; > > + u64 mem_size; > > > > len = (len >= COMMAND_LINE_SIZE) ? COMMAND_LINE_SIZE - 1 : len; > > memcpy(tmp_cmdline, args, len); > > @@ -195,8 +208,18 @@ 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) > > + return -EINVAL; > > + mem_limit = mem_size; > > + } > > } > > > > return 0; > > @@ -432,7 +455,8 @@ static void process_e820_entry(struct e820entry *entry, > > { > > struct mem_vector region, overlap; > > struct slot_area slot_area; > > - unsigned long start_orig; > > + unsigned long start_orig, end; > > + struct e820entry cur_entry; > > > > /* Skip non-RAM entries. */ > > if (entry->type != E820_RAM) > > @@ -446,8 +470,15 @@ static void process_e820_entry(struct e820entry *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 - 1, mem_limit); > > + if (entry->addr >= end) > > + return; > > + cur_entry.addr = entry->addr; > > + cur_entry.size = end - entry->addr + 1; > > + > > + region.start = cur_entry.addr; > > + region.size = cur_entry.size; > > I find the manipulation of entry->addr +/- 1 confusing; it should just > be mem_limit that is adjusted: > > end = min(entry->size + entry->addr, mem_limit + 1);
The first one is preferred. Since if no memory limit specifed, we still have a limit, 64T-1 or UULONG_MAX -1, in logic more understandable. And in code lines it's less.
Will change with your suggestion.
Thanks a log for your comments!
> > And maybe to avoid mem_limit being giant by default, maybe have "0" be special? > > cur_entry.addr = entry->addr; > if (mem_limit) { > unsigned long end = min(entry->size + entry->addr, mem_limit + 1); > if (entry->addr > end) > return; > cur_entry.size = end - entry->addr; > } else { > cur_entry.size = entry->size; > } > > or something... and maybe move the whole thing earlier so other tests > that examine entry->size are checked with the new adjusted value. > > -Kees > > > > > /* Give up if slot area array is full. */ > > while (slot_area_index < MAX_SLOT_AREA) { > > @@ -461,7 +492,7 @@ static void process_e820_entry(struct e820entry *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 > > > > > > -- > Kees Cook > Pixel Security
| |