Re: [tip:x86/boot] x86/boot: Early parse RSDP and save it in boot_params

[Ard Biesheuvel]

On Mon, 11 Feb 2019 at 01:22, Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Fri, Feb 08, 2019 at 10:53:22PM +0100, Borislav Petkov wrote:
> > On Fri, Feb 08, 2019 at 12:44:51PM -0800, Guenter Roeck wrote:
> > > Yes, the kernel boots if I comment out that function and have it return 0.
> >
> > Thanks, this localizes the issue significantly.
>
> Some observations:
>
>                 } else {
>                         efi_config_table_32_t *tmp_table;
>
>                         tmp_table = config_tables;
>                         guid = tmp_table->guid;                 <--- *
>                         table = tmp_table->table;
>                 }
>
> It blows up at that tmp_table->guid deref above. Singlestepping through
> it with gdb shows:
>
> # arch/x86/boot/compressed/acpi.c:114:                  guid = tmp_table->guid;
>         movq    (%rdi), %rax    # MEM[(struct efi_config_table_32_t *)config_tables_37].guid, guid
>         movq    8(%rdi), %rsi   # MEM[(struct efi_config_table_32_t *)config_tables_37].guid, guid
> # arch/x86/boot/compressed/acpi.c:115:                  table = tmp_table->table;
>         movl    16(%rdi), %r10d # MEM[(struct efi_config_table_32_t *)config_tables_37].table, table
>         jmp     .L30    #
>
> and %rdi has:
>
>         rdi            0x630646870
>
> which is an address above 4G but we're using a 32-bit EFI BIOS.
>
> Which begs the question whether EFI system tables can even be mapped at
> something above 4G with a 32-bit EFI and whether that could work ok.
> Hmm.
>
> Lemme add Ard and mfleming for insight here.
>

-ENOCONTEXT, but let me try in any case:

linux/efi.h has

typedef struct {
  efi_guid_t guid;
  u32 table;
} efi_config_table_32_t;

so if we end up with more than 32 bits set in table, there is
something seriously wrong.

The size of efi_config_table_32_t deviates from efi_config_table_64_t,
so you will have to ensure that you are using the correct stride when
iterating over config_tables.