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

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Message-ID: <CAKv+Gu_r4Vz2BRpRyJ=UsM1r-+CbyP6heggL+qsKKhJ_iTWhFg@mail.gmail.com>
Date:   Mon, 11 Feb 2019 09:57:02 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
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, 11 Feb 2019 at 10:56, Chao Fan <fanc.fnst@...fujitsu.com> 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@...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.
>

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 ?