Re: [PATCH v4 2/2] x86/boot/KASLR: skip the specified crashkernel region

[Pingfan Liu]

On Wed, Apr 17, 2019 at 3:01 AM Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Mon, Apr 08, 2019 at 01:58:35PM +0800, Pingfan Liu wrote:
> > crashkernel=x@y or or =range1:size1[,range2:size2,...]@offset option may
> > fail to reserve the required memory region if KASLR puts kernel into the
> > region. To avoid this uncertainty, asking KASLR to skip the required
> > region.
> >
> > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: Baoquan He <bhe@xxxxxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > Cc: Nicolas Pitre <nico@xxxxxxxxxx>
> > Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> > Cc: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> > CC: Hari Bathini <hbathini@xxxxxxxxxxxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >  arch/x86/boot/compressed/kaslr.c | 40 ++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 40 insertions(+)
> >
> > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> > index 2e53c05..765a593 100644
> > --- a/arch/x86/boot/compressed/kaslr.c
> > +++ b/arch/x86/boot/compressed/kaslr.c
> > @@ -107,6 +107,7 @@ enum mem_avoid_index {
> >       MEM_AVOID_BOOTPARAMS,
> >       MEM_AVOID_MEMMAP_BEGIN,
> >       MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
> > +     MEM_AVOID_CRASHKERNEL,
> >       MEM_AVOID_MAX,
> >  };
> >
> > @@ -131,6 +132,11 @@ char *skip_spaces(const char *str)
> >  }
> >  #include "../../../../lib/ctype.c"
> >  #include "../../../../lib/cmdline.c"
> > +#ifdef CONFIG_CRASH_CORE
> > +#define printk
> > +#define _BOOT_KASLR
> > +#include "../../../../lib/parse_crashkernel.c"
> > +#endif
> >
> >  static int
> >  parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
> > @@ -292,6 +298,39 @@ static void handle_mem_options(void)
> >       return;
> >  }
> >
> > +static u64 mem_ram_size(void)
> > +{
> > +     struct boot_e820_entry *entry;
> > +     u64 total_sz = 0;
> > +     int i;
> > +
> > +     for (i = 0; i < boot_params->e820_entries; i++) {
> > +             entry = &boot_params->e820_table[i];
> > +             /* Skip non-RAM entries. */
> > +             if (entry->type != E820_TYPE_RAM)
> > +                     continue;
> > +             total_sz += entry->size;
> > +     }
> > +     return total_sz;
> > +}
> > +
> > +/*
> > + * For crashkernel=size@offset or =range1:size1[,range2:size2,...]@offset
> > + * options, recording mem_avoid for them.
> > + */
> > +static void handle_crashkernel_options(void)
> > +{
> > +     unsigned long long crash_size, crash_base = 0;
> > +     char *cmdline = (char *)get_cmd_line_ptr();
> > +     u64 total_sz = mem_ram_size();
> > +
> > +     parse_crashkernel(cmdline, total_sz, &crash_size, &crash_base);
>
> That function has a return value which you could test. And then you
> don't need to set crash_base to 0 above.
>
Take __parse_crashkernel()->parse_crashkernel_simple() for example. If
no offset given, then it still return 0, but crash_base is dangling.

Regards,
Pingfan