linux-kernel - Re: [RFC] efi/tpm: add efi.tpm_log as a reserved region in 820_table

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Message-ID: <CAMj1kXEXH2YvWtzEJEEOnTLqACsRhan3Lf9OCLYDjKf6gxDmBQ@mail.gmail.com>
Date: Sat, 14 Sep 2024 10:31:03 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Dave Young <dyoung@...hat.com>
Cc: Usama Arif <usamaarif642@...il.com>, Breno Leitao <leitao@...ian.org>, linux-efi@...r.kernel.org, 
	kexec@...ts.infradead.org, ebiederm@...ssion.com, bhe@...hat.com, 
	vgoyal@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com, 
	x86@...nel.org, linux-kernel@...r.kernel.org, rmikey@...a.com, 
	gourry@...rry.net
Subject: Re: [RFC] efi/tpm: add efi.tpm_log as a reserved region in 820_table_firmware

On Sat, 14 Sept 2024 at 08:46, Dave Young <dyoung@...hat.com> wrote:
>
> On Fri, 13 Sept 2024 at 18:56, Dave Young <dyoung@...hat.com> wrote:
> >
> > On Thu, 12 Sept 2024 at 22:15, Ard Biesheuvel <ardb@...nel.org> wrote:
> > >
> > > (cc Dave)
> >
> > Thanks for ccing me.
> >
> > >
> > > Full thread here:
> > > https://lore.kernel.org/all/CAMj1kXG1hbiafKRyC5qM1Vj5X7x-dmLndqqo2AYnHMRxDz-80w@mail.gmail.com/T/#u
> > >
> > > On Thu, 12 Sept 2024 at 16:05, Ard Biesheuvel <ardb@...nel.org> wrote:
> > > >
> > > > On Thu, 12 Sept 2024 at 15:55, Usama Arif <usamaarif642@...il.com> wrote:
> > > > >
> > > > >
> > > > >
> > > > > On 12/09/2024 14:10, Ard Biesheuvel wrote:
> > > > > > Does the below help at all?
> > > > > >
> > > > > > --- a/drivers/firmware/efi/tpm.c
> > > > > > +++ b/drivers/firmware/efi/tpm.c
> > > > > > @@ -60,7 +60,7 @@ int __init efi_tpm_eventlog_init(void)
> > > > > >         }
> > > > > >
> > > > > >         tbl_size = sizeof(*log_tbl) + log_tbl->size;
> > > > > > -       memblock_reserve(efi.tpm_log, tbl_size);
> > > > > > +       efi_mem_reserve(efi.tpm_log, tbl_size);
> > > > > >
> > > > > >         if (efi.tpm_final_log == EFI_INVALID_TABLE_ADDR) {
> > > > > >                 pr_info("TPM Final Events table not present\n");
> > > > >
> > > > > Unfortunately not. efi_mem_reserve updates e820_table, while kexec looks at /sys/firmware/memmap
> > > > > which is e820_table_firmware.
> > > > >
> > > > > arch_update_firmware_area introduced in the RFC patch does the same thing as efi_mem_reserve does at
> > > > > its end, just with e820_table_firmware instead of e820_table.
> > > > > i.e. efi_mem_reserve does:
> > > > >         e820__range_update(addr, size, E820_TYPE_RAM, E820_TYPE_RESERVED);
> > > > >         e820__update_table(e820_table);
> > > > >
> > > > > while arch_update_firmware_area does:
> > > > >         e820__range_update_firmware(addr, size, E820_TYPE_RAM, E820_TYPE_RESERVED);
> > > > >         e820__update_table(e820_table_firmware);
> > > > >
> > > >
> > > > Shame.
> > > >
> > > > Using efi_mem_reserve() is appropriate here in any case, but I guess
> > > > kexec on x86 needs to be fixed to juggle the EFI memory map, memblock
> > > > table, and 3 (!) versions of the E820 table in the correct way
> > > > (e820_table, e820_table_kexec and e820_table_firmware)
> > > >
> > > > Perhaps we can put this additional logic in x86's implementation of
> > > > efi_arch_mem_reserve()? AFAICT, all callers of efi_mem_reserve() deal
> > > > with configuration tables produced by the firmware that may not be
> > > > reserved correctly if kexec looks at e820_table_firmware[] only.
> > >
> >
> > I have not read all the conversations,  let me have a look and response later.
> >
>
> I'm still confused after reading the code about why this issue can
> still happen with a efi_mem_reserve.
> Usama, Breno, could any of you share the exact steps on how to
> reproduce this issue with a kvm guest?
>

The code does not use efi_mem_reserve() only memblock_reserve().