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

[Chao Fan]

On Mon, Feb 11, 2019 at 09:57:02AM +0000, Ard Biesheuvel wrote:
>On Mon, 11 Feb 2019 at 10:56, Chao Fan <fanc.fnst@xxxxxxxxxxxxxx> wrote:
>>
>> On Mon, Feb 11, 2019 at 09:46:03AM +0000, Ard Biesheuvel wrote:
>> >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.
>>
>> Here I use signature to judge it.
>> If the signature is EFI64_LOADER_SIGNATURE, I will use efi_config_table_64_t,
>> if the signature is EFI32_LOADER_SIGNATURE, I will use efi_config_table_32_t.
>> But the efi32 whose signature is EFI32_LOADER_SIGNATURE points to a
>> address above 4G, I am not sure whether this is normal and works well.
>>
>
>This is impossible. The 'table' member of efi_config_table_32_t is
>only 32 bits wide, so how can it contain an address over 4 GB ?

Maybe I mislead you. In my code, I need to find the eficonfig_table_*.
After that, I should type cast it to right
efi_config_table_32_t or efi_config_table_64_t.

Then my judgment is to compare its efi_info->efi_loader_signature.
If it's EFI64_LOADER_SIGNATURE, I will type cast it to efi_config_table_64_t.
If it's EFI32_LOADER_SIGNATURE, I will type cast it to efi_config_table_32_t.

But here is a issue, its signature matches EFI32_LOADER_SIGNATURE, but
it's table member is above 4G, but I use efi_config_table_32_t. That cause a problem.

Thanks,
Chao Fan

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