linux-kernel - Re: [PATCH v5 4/4] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

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Date:   Tue, 18 Jul 2017 07:51:28 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, izumi.taku@...fujitsu.com,
        fanc.fnst@...fujitsu.com, Thomas Garnier <thgarnie@...gle.com>,
        n-horiguchi@...jp.nec.com
Subject: Re: [PATCH v5 4/4] x86/boot/KASLR: Restrict kernel to be randomized
 in mirror regions

On 07/17/17 at 04:13pm, Kees Cook wrote:
> > +#ifdef CONFIG_EFI
> > +/*
> > + * Returns true if mirror region found (and must have been processed
> > + * for slots adding)
> > + */
> > +static bool process_efi_entries(unsigned long minimum,
> > +                               unsigned long image_size)
> > +{
> > +       struct efi_info *e = &boot_params->efi_info;
> > +       bool efi_mirror_found = false;
> > +       struct mem_vector region;
> > +       efi_memory_desc_t *md;
> > +       unsigned long pmap;
> > +       char *signature;
> > +       u32 nr_desc;
> > +       int i;
> > +
> > +       signature = (char *)&boot_params->efi_info.efi_loader_signature;
> > +       if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
> > +           strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
> > +               return false;
> > +
> > +#ifdef CONFIG_X86_32
> > +       /* Can't handle data above 4GB at this time */
> > +       if (e->efi_memmap_hi) {
> > +               warn("Memory map is above 4GB, EFI should be disabled.\n");
> > +               return false;
> > +       }
> > +       pmap =  e->efi_memmap;
> > +#else
> > +       pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
> > +#endif
> > +
> > +       nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
> > +       for (i = 0; i < nr_desc; i++) {
> > +               md = (efi_memory_desc_t *)(pmap + (i * e->efi_memdesc_size));
> > +               if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
> > +                       region.start = md->phys_addr;
> > +                       region.size = md->num_pages << EFI_PAGE_SHIFT;
> > +                       process_mem_region(&region, minimum, image_size);
> > +                       efi_mirror_found = true;
> > +
> > +                       if (slot_area_index == MAX_SLOT_AREA) {
> > +                               debug_putstr("Aborted efi scan (slot_areas full)!\n");
> 
> Should this text be capitalized to "EFI" or expanded to "EFI mirror"?

Yeah, this should be capitalized. And it should be EFI mirror here, just
later Naoya will add other features about EFI, not only EFI mirror. Let
me change it to EFI mirror, and Naoya can rebase on it.

Many thanks for your reviewing, Kees!

> 
> > +                               break;
> > +                       }
> > +               }
> > +       }
> > +
> > +       return efi_mirror_found;
> > +}
> > +#else
> > +static inline bool process_efi_entries(unsigned long minimum,
> > +                                      unsigned long image_size)
> > +{
> > +       return false;
> > +}
> > +#endif
> > +
> >  static void process_e820_entries(unsigned long minimum,
> >                                  unsigned long image_size)
> >  {
> > @@ -586,13 +647,16 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
> >  {
> >         /* Check if we had too many memmaps. */
> >         if (memmap_too_large) {
> > -               debug_putstr("Aborted e820 scan (more than 4 memmap= args)!\n");
> > +               debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
> >                 return 0;
> >         }
> >
> >         /* Make sure minimum is aligned. */
> >         minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
> >
> > +       if(process_efi_entries(minimum, image_size))
> 
> Style nit: space between "if" and "(".

Will change, could I forget running checkpatch script.

> 
> > +               return slots_fetch_random();
> > +
> >         process_e820_entries(minimum, image_size);
> >         return slots_fetch_random();
> >  }
> > @@ -652,7 +716,7 @@ void choose_random_location(unsigned long input,
> >          */
> >         min_addr = min(*output, 512UL << 20);
> >
> > -       /* Walk e820 and find a random address. */
> > +       /* Walk available memory entries to find a random address. */
> >         random_addr = find_random_phys_addr(min_addr, output_size);
> >         if (!random_addr) {
> >                 warn("Physical KASLR disabled: no suitable memory region!");
> > --
> > 2.5.5
> >
> 
> Otherwise, looks fine to me for the KASLR piece; I can't speak
> specifically to the EFI logic. :)
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>

I will repost with the clean up change and adding your Reviewed-by
since no functionality change. Will see if there will be any EFI
related comment.

Thanks again for reviewing and great suggestions!

Thanks
Baoquan