From: Juergen Gross <jgross@suse.com>
To: "H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org,
x86@kernel.org, linux-doc@vger.kernel.org
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
corbet@lwn.net, boris.ostrovsky@oracle.com
Subject: Re: PLEASE REVERT URGENTLY: Re: [PATCH v5 2/3] x86/boot: add acpi rsdp address to setup_header
Date: Sat, 10 Nov 2018 16:22:29 +0100 [thread overview]
Message-ID: <685b425b-c816-4f65-3393-b48e59d170d8@suse.com> (raw)
In-Reply-To: <f7c78ee7-b548-7f04-24da-7321b6c64c97@zytor.com>
On 09/11/2018 23:23, H. Peter Anvin wrote:
> I just noticed this patch -- I missed it because the cover message
> seemed far more harmless so I didn't notice this change.
>
> THIS PATCH IS FATALLY WRONG AND NEEDS TO BE IMMEDIATELY REVERTED BEFORE
> ANYONE STARTS RELYING ON IT; IT HAS THE POTENTIAL OF BREAKING THE
> BOOTLOADER PROTOCOL FOR ALL FUTURE.
>
> It seems to be based on fundamental misconceptions about the various
> data structures in the protocol, and does so in a way that completely
> breaks the way the protocol is designed to work.
>
> The protocol is specifically designed such that fields are not version
> dependencies. The version number is strictly to inform the boot loader
> about which capabilities the kernel has, so that the boot loader can
> know if a certain data field is meaningful and/or honored.
>
>> +Protocol 2.14: (Kernel 4.20) Added acpi_rsdp_addr holding the physical
>> + address of the ACPI RSDP table.
>> + The bootloader updates version with:
>> + 0x8000 | min(kernel-version, bootloader-version)
>> + kernel-version being the protocol version supported by
>> + the kernel and bootloader-version the protocol version
>> + supported by the bootloader.
>
> [...]
>
>> **** MEMORY LAYOUT
>>
>> The traditional memory map for the kernel loader, used for Image or
>> @@ -197,6 +209,7 @@ Offset Proto Name Meaning
>> 0258/8 2.10+ pref_address Preferred loading address
>> 0260/4 2.10+ init_size Linear memory required during initialization
>> 0264/4 2.11+ handover_offset Offset of handover entry point
>> +0268/8 2.14+ acpi_rsdp_addr Physical address of RSDP table
>
> NO.
>
> That is not how struct setup_header works, nor does this belong here.
>
> struct setup_header contains *initialized data*, and has a length byte
> at offset 0x201. The bootloader is responsible for copying the full
> structure into the appropriate offset (0x1f1) in struct boot_params.
>
> The length byte isn't actually a requirement, since the maximum possible
> size of this structure is 144 bytes, and the kernel will (obviously) not
> look at the older fields anyway, but it is good practice. The kernel or
> any other entity is free to zero out the bytes past this length pointer.
>
> There are only 24 bytes left in this structure, and this would occupy 8
> of them for no valid reason. The *only* valid reason to put a
> zero-initialized field in struct setup_header is if it used by the
> 16-bit legacy BIOS boot, which is obviously not the case here.
>
> This field thus belongs in struct boot_params, not struct setup_header.
Would you be okay with putting acpi_rsdp_addr at offset 0x0cc (_pad4)?
Juergen
next prev parent reply other threads:[~2018-11-10 15:22 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-10 6:14 [PATCH v5 0/3] x86: make rsdp address accessible via boot params Juergen Gross
2018-10-10 6:14 ` [PATCH v5 1/3] x86/xen: fix boot loader version reported for pvh guests Juergen Gross
2018-10-10 6:14 ` [PATCH v5 2/3] x86/boot: add acpi rsdp address to setup_header Juergen Gross
2018-11-09 22:23 ` PLEASE REVERT URGENTLY: " H. Peter Anvin
2018-11-10 0:38 ` H. Peter Anvin
2018-11-10 6:26 ` Juergen Gross
2018-11-10 6:32 ` H. Peter Anvin
2018-11-10 7:02 ` Juergen Gross
2018-11-10 7:16 ` H. Peter Anvin
2018-11-10 9:03 ` Juergen Gross
2018-11-11 18:49 ` H. Peter Anvin
2018-11-19 16:48 ` Konrad Rzeszutek Wilk
2018-11-10 15:22 ` Juergen Gross [this message]
2018-11-11 23:58 ` hpa
2018-10-10 6:14 ` [PATCH v5 3/3] x86/acpi: take rsdp address for boot params if available Juergen Gross
2018-10-10 6:23 ` [PATCH v5 0/3] x86: make rsdp address accessible via boot params Ingo Molnar
2018-10-10 6:39 ` Juergen Gross
2018-10-10 7:19 ` Ingo Molnar
2018-10-10 7:28 ` Juergen Gross
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