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

[Borislav Petkov]

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.

Thx.

-- 
Regards/Gruss,
    Boris.

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