linux-kernel - Re: [tip:x86/boot] x86/boot: Early parse RSDP and save it in boot

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Message-ID: <20190211095547.GB1651@localhost.localdomain>
Date:   Mon, 11 Feb 2019 17:55:48 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC:     Borislav Petkov <bp@...en8.de>, Guenter Roeck <linux@...ck-us.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        "Lendacky, Thomas" <thomas.lendacky@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        <caoj.fnst@...fujitsu.com>, Juergen Gross <jgross@...e.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        <linux-tip-commits@...r.kernel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [tip:x86/boot] x86/boot: Early parse RSDP and save it in
 boot_params

On Mon, Feb 11, 2019 at 09:46:03AM +0000, Ard Biesheuvel wrote:
>On Mon, 11 Feb 2019 at 01:22, Borislav Petkov <bp@...en8.de> 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.

Thanks,
Chao Fan

>
>