Messages in this thread | | | Subject | Re: [PATCH Part1 RFC v3 20/22] x86/boot: Add Confidential Computing address to setup_header | From | "Kuppuswamy, Sathyanarayanan" <> | Date | Thu, 24 Jun 2021 06:09:28 -0700 |
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+ Andi, Kirill (For TDX specific review)
On 6/23/21 8:19 PM, Michael Roth wrote: > On Wed, Jun 23, 2021 at 12:22:23PM +0200, Borislav Petkov wrote: >> On Tue, Jun 22, 2021 at 11:30:43PM -0500, Michael Roth wrote: >>> Quoting Borislav Petkov (2021-06-18 10:05:28) >>>> On Fri, Jun 18, 2021 at 08:57:12AM -0500, Brijesh Singh wrote: >>>>> Don't have any strong reason to keep it separate, I can define a new >>>>> type and use the setup_data to pass this information. >>>> >>>> setup_data is exactly for use cases like that - pass a bunch of data >>>> to the kernel. So there's no need for a separate thing. Also see that >>>> kernel_info thing which got added recently for read_only data. >>> >>> Hi Boris, >>> >>> There's one side-effect to this change WRT the CPUID page (which I think >>> we're hoping to include in RFC v4). >>> >>> With CPUID page we need to access it very early in boot, for both >>> boot/compressed kernel, and the uncompressed kernel. At first this was >>> implemented by moving the early EFI table parsing code from >>> arch/x86/kernel/boot/compressed/acpi.c into a little library to handle early >>> EFI table parsing to fetch the Confidential Computing blob to get the CPUID >>> page address. >>> >>> This was a bit messy since we needed to share that library between >>> boot/compressed and uncompressed, and at that early stage things like >>> fixup_pointer() are needed in some places, else even basic things like >>> accessing EFI64_LOADER_SIGNATURE and various EFI helper functions could crash >>> in uncompressed otherwise, so the library code needed to be fixed up >>> accordingly. >>> >>> To simplify things we ended up simply keeping the early EFI table parsing in >>> boot/compressed, and then having boot/compressed initialize >>> setup_data.cc_blob_address so that the uncompressed kernel could access it >>> from there (acpi does something similar with rdsp address). >> >> Yes, except the rsdp address is not vendor-specific but an x86 ACPI >> thing, so pretty much omnipresent. >> >> Also, acpi_rsdp_addr is part of boot_params and that struct is full >> of padding holes and obsolete members so reusing a u32 there is a lot >> "easier" than changing the setup_header. So can you put that address in >> boot_params instead? > > Thanks for the suggestion! I tried something like the below and that seems to > work pretty well. I'm not sure if that's the best spot or not though, it > seems like it might be a good idea to leave some padding after eddbuf in > case it needs to grow in the future. I'll look into that a bit more. > > One downside to this is we still need something in the boot protocol, > either via setup_data, or setup_header directly. Having it in > setup_header avoids the need to also have to add a field to boot_params > for the boot/compressed->uncompressed passing, but maybe that's not a good > enough justification. Perhaps if the TDX folks have similar needs though. > > diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h > index 1ac5acca72ce..0824c8646861 100644 > --- a/arch/x86/include/uapi/asm/bootparam.h > +++ b/arch/x86/include/uapi/asm/bootparam.h > @@ -218,7 +218,8 @@ struct boot_params { > struct boot_e820_entry e820_table[E820_MAX_ENTRIES_ZEROPAGE]; /* 0x2d0 */ > __u8 _pad8[48]; /* 0xcd0 */ > struct edd_info eddbuf[EDDMAXNR]; /* 0xd00 */ > - __u8 _pad9[276]; /* 0xeec */ > + __u32 cc_blob_address; /* 0xeec */ > + __u8 _pad9[272]; /* 0xef0 */ > } __attribute__((packed)); > > diff --git a/arch/x86/include/asm/bootparam_utils.h b/arch/x86/include/asm/bootparam_utils.h > index 981fe923a59f..53e9b0620d96 100644 > --- a/arch/x86/include/asm/bootparam_utils.h > +++ b/arch/x86/include/asm/bootparam_utils.h > @@ -74,6 +74,7 @@ static void sanitize_boot_params(struct boot_params *boot_params) > BOOT_PARAM_PRESERVE(hdr), > BOOT_PARAM_PRESERVE(e820_table), > BOOT_PARAM_PRESERVE(eddbuf), > + BOOT_PARAM_PRESERVE(cc_blob_address), > }; > > memset(&scratch, 0, sizeof(scratch)); > >> >>> Now that we're moving it to setup_data, this becomes a bit more awkward, >>> since we need to reserve memory in boot/compressed to store the setup_data >>> entry, then add it to the linked list to pass along to uncompressed kernel. >>> In turn that also means we need to add an identity mapping for this in >>> ident_map_64.c, so I'm not sure that's the best approach. >>> >>> So just trying to pin what the best approach is: >>> >>> a) move cc_blob to setup_data, and do the above-described to pass >>> cc_blob_address from boot/compressed to uncompressed to avoid early >>> EFI parsing in uncompressed >>> b) move cc_blob to setup_data, and do the EFI table parsing in both >>> boot/compressed. leave setup_data allocation/init for BIOS/bootloader >>> c) keep storing cc_blob_address in setup_header.cc_blob_address >>> d) something else? >> >> Leaving in the whole text for newly CCed TDX folks in case they're going >> to need something like that. >> >> And if so, then both vendors should even share the field definition. >> >> Dave, Sathya, you can find the whole subthread here: >> >> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20210602140416.23573-21-brijesh.singh%40amd.com&data=04%7C01%7Cmichael.roth%40amd.com%7C3b352c4b944c4d95bbdb08d93630d0eb%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637600405622460196%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=464O7JxibsbjC3bc0LkGcztdb4kCYH7kcQAcqohJhug%3D&reserved=0 >> >> in case you need background info on the topic at hand. >> >> Thx. >> >> -- >> Regards/Gruss, >> Boris. >> >> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpeople.kernel.org%2Ftglx%2Fnotes-about-netiquette&data=04%7C01%7Cmichael.roth%40amd.com%7C3b352c4b944c4d95bbdb08d93630d0eb%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637600405622460196%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ruCM7CNgPCNPkrOoiNts1ZKi5k7JSUumln7qQMP%2BMi0%3D&reserved=0
-- Sathyanarayanan Kuppuswamy Linux Kernel Developer
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