linux-kernel - Re: [PATCH v8 0/3] Introduce 64b relocatable kernel

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Date:   Mon, 20 Feb 2023 10:14:09 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Alexandre Ghiti <alexghiti@...osinc.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: Re: [PATCH v8 0/3] Introduce 64b relocatable kernel

Alexandre Ghiti <alexghiti@...osinc.com> writes:

> After multiple attempts, this patchset is now based on the fact that the
> 64b kernel mapping was moved outside the linear mapping.
>
> The first patch allows to build relocatable kernels but is not selected
> by default. That patch is a requirement for KASLR.
> The second and third patches take advantage of an already existing powerpc
> script that checks relocations at compile-time, and uses it for riscv.
>
> This patchset is rebased on top of:
>
> RISC-V kasan rework (https://lore.kernel.org/lkml/Y6TTvku%2FyuSjm42j@spud/T/)
> riscv: Use PUD/P4D/PGD pages for the linear mapping (https://lore.kernel.org/lkml/20230125114229.hrhsyw4aegrnmoau@orel/T/)
> riscv: Allow to downgrade paging mode from the command line (https://lore.kernel.org/lkml/CAHVXubjeSMvfTPnvrnYRupOGx6+vUvUGfRS3piTeo=TH2cHKNg@mail.gmail.com/)
> base-commit-tag: v6.2-rc7
>
> Changes in v8:
>   * Fix UEFI boot by moving rela.dyn section into the data so that PE/COFF
>     loader actually copies the relocations too
>   * Fix check that used PGDIR instead of PUD which was not correct
>     for sv48 and sv57
>   * Fix PE/COFF header data size definition as it led to size of 0
>
> Changes in v7:
>   * Rebase on top of v5.15
>   * Fix LDFLAGS_vmlinux which was overriden when CONFIG_DYNAMIC_FTRACE was
>     set
>   * Make relocate_kernel static
>   * Add Ack from Michael
>
> Changes in v6:
>   * Remove the kernel move to vmalloc zone
>   * Rebased on top of for-next
>   * Remove relocatable property from 32b kernel as the kernel is mapped in
>     the linear mapping and would then need to be copied physically too
>   * CONFIG_RELOCATABLE depends on !XIP_KERNEL
>   * Remove Reviewed-by from first patch as it changed a bit
>
> Changes in v5:
>   * Add "static __init" to create_kernel_page_table function as reported by
>     Kbuild test robot
>   * Add reviewed-by from Zong
>   * Rebase onto v5.7
>
> Changes in v4:
>   * Fix BPF region that overlapped with kernel's as suggested by Zong
>   * Fix end of module region that could be larger than 2GB as suggested by Zong
>   * Fix the size of the vm area reserved for the kernel as we could lose
>     PMD_SIZE if the size was already aligned on PMD_SIZE
>   * Split compile time relocations check patch into 2 patches as suggested by Anup
>   * Applied Reviewed-by from Zong and Anup
>
> Changes in v3:
>   * Move kernel mapping to vmalloc
>
> Changes in v2:
>   * Make RELOCATABLE depend on MMU as suggested by Anup
>   * Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
>   * Use __pa_symbol instead of __pa, as suggested by Zong
>   * Rebased on top of v5.6-rc3
>   * Tested with sv48 patchset
>   * Add Reviewed/Tested-by from Zong and Anup
>
> Alexandre Ghiti (3):
>   riscv: Introduce CONFIG_RELOCATABLE
>   powerpc: Move script to check relocations at compile time in scripts/
>   riscv: Check relocations at compile time

I'm getting issues booting via UEFI/efi-stub with this, because the PE
header is messed up.

from arch/riscv/kernel/efi-header.S:

 | ...
 | extra_header_fields:
 |         .quad   0                                       // ImageBase
 |         .long   PECOFF_SECTION_ALIGNMENT                // SectionAlignment
 |         .long   PECOFF_FILE_ALIGNMENT                   // FileAlignment
 | ...

PECOFF* is taken from the linker-script, and ends up in relocation
section. When u-boot tried to load the image, alignment is zero and the
loader breaks.


Björn