linux-kernel - Re: [PATCH v15 4/6] x86/boot: Introduce bios_get_rsdp

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Message-ID: <20190111012718.GE2216@localhost.localdomain>
Date:   Fri, 11 Jan 2019 09:27:18 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
        <keescook@...omium.org>, <bhe@...hat.com>, <msys.mizuma@...il.com>,
        <indou.takao@...fujitsu.com>, <caoj.fnst@...fujitsu.com>
Subject: Re: [PATCH v15 4/6] x86/boot: Introduce bios_get_rsdp_addr() to
 search RSDP in memory

On Thu, Jan 10, 2019 at 10:27:47PM +0100, Borislav Petkov wrote:
>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@...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;

Thanks, will change that.

>
>> +
>> +	/* 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.

Will drop it.

Thanks,
Chao Fan

>
>> +	if (rsdp) {
>> +		address = (u32)(ACPI_HI_RSDP_WINDOW_BASE +
>> +				ACPI_PTR_DIFF(rsdp, table_ptr));
>> +		return address;
>> +	}
>> +	return 0;
>> +}
>
>-- 
>Regards/Gruss,
>    Boris.
>
>Good mailing practices for 400: avoid top-posting and trim the reply.
>
>