Re: [PATCH v15 4/6] x86/boot: Introduce bios_get_rsdp_addr() to search RSDP in memory

Borislav Petkov
2019-01-10T21:28:00Z

On Mon, Jan 07, 2019 at 11:22:41AM +0800, Chao Fan wrote:
> Memory information in SRAT table is necessary to fix the conflict
> between KASLR and memory-hotremove. So RSDP and SRAT should be parsed.
>
> When booting form KEXEC/EFI/BIOS, the methods to compute RSDP
> are different. When booting from BIOS, there is no variable who can
> point to RSDP directly, so scan memory for the RSDP and verify RSDP
> by signature and checksum.
>
> Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
> ---
> arch/x86/boot/compressed/acpi.c | 86 +++++++++++++++++++++++++++++++++
> 1 file changed, 86 insertions(+)

...

> +/* Search RSDP address, based on acpi_find_root_pointer(). */
> +static acpi_physical_address bios_get_rsdp_addr(void)
> +{
> + u8 *table_ptr;
> + u32 address;
> + u8 *rsdp;

But those u8's together:

u8 *table_ptr, *rsdp;
u32 address;

> +
> + /* Get the location of the Extended BIOS Data Area (EBDA) */
> + table_ptr = (u8 *)ACPI_EBDA_PTR_LOCATION;
> + address = *(u16 *)table_ptr;
> + address <<= 4;
> + table_ptr = (u8 *)(long)address;
> +
> + /*
> + * Search EBDA paragraphs (EBDA is required to be a minimum of
> + * 1K length)
> + */
> + if (address > 0x400) {
> + rsdp = scan_mem_for_rsdp(table_ptr, ACPI_EBDA_WINDOW_SIZE);
> + if (rsdp) {
> + address += (u32)ACPI_PTR_DIFF(rsdp, table_ptr);
> + return address;
> + }
> + }
> +
> + /* Search upper memory: 16-byte boundaries in E0000h-FFFFFh */
> + table_ptr = (u8 *)ACPI_HI_RSDP_WINDOW_BASE;
> + rsdp = scan_mem_for_rsdp(table_ptr, ACPI_HI_RSDP_WINDOW_SIZE);
> +

Superfluous newline.

> + if (rsdp) {
> + address = (u32)(ACPI_HI_RSDP_WINDOW_BASE +
> + ACPI_PTR_DIFF(rsdp, table_ptr));
> + return address;
> + }
> + return 0;
> +}

--
Regards/Gruss,
Boris.

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