Messages in this thread | | | Date | Sat, 29 Apr 2017 18:14:46 +0800 | From | Baoquan He <> | Subject | Re: [PATCH v3 2/3] KASLR: Handle memory limit specified by memmap and mem option |
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On 04/28/17 at 12:39pm, Kees Cook wrote: > On Wed, Apr 26, 2017 at 3:16 AM, 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> > > 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; > > Please explicitly add a comment like /* Fall through. */ or something > here, to help future reviewers. :)
Sure, will add. Thanks!
> > > + 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 > > > > Otherwise, this looks good to me. > > -Kees > > -- > Kees Cook > Pixel Security
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