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In-Reply-To: <b67e091d-7be0-7f8b-4ef2-0a97936a1d34@ghiti.fr>
From:   Alexandre Ghiti <alexandre.ghiti@canonical.com>
Date:   Fri, 18 Feb 2022 11:47:00 +0100
Message-ID: <CA+zEjCurCYeOdPdfJ23MwhJXE4ApQ+m3oHvs_ge8Jz5PYM45OA@mail.gmail.com>
Subject: Re: [PATCH v7 1/3] riscv: Introduce CONFIG_RELOCATABLE
To:     Alexandre ghiti <alex@ghiti.fr>
Cc:     Palmer Dabbelt <palmer@dabbelt.com>, mpe@ellerman.id.au,
        benh@kernel.crashing.org, paulus@samba.org,
        Paul Walmsley <paul.walmsley@sifive.com>,
        aou@eecs.berkeley.edu, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org
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Hi Palmer,

Do you intend to pull that in for-next or not yet? Can I do something to help?

Thanks,

Alex

On Mon, Jan 10, 2022 at 9:05 AM Alexandre ghiti <alex@ghiti.fr> wrote:
>
> Hi Palmer,
>
> Do you think this could go in for-next?
>
> Thanks,
>
> Alex
>
> On 12/6/21 10:44, Alexandre ghiti wrote:
> > @Palmer, can I do anything for that to be pulled in 5.17?
> >
> > Thanks,
> >
> > Alex
> >
> > On 10/27/21 07:04, Alexandre ghiti wrote:
> >> Hi Palmer,
> >>
> >> On 10/26/21 11:29 PM, Palmer Dabbelt wrote:
> >>> On Sat, 09 Oct 2021 10:20:20 PDT (-0700), alex@ghiti.fr wrote:
> >>>> Arf, I have sent this patchset with the wrong email address. @Palmer
> >>>> tell me if you want me to resend it correctly.
> >>> Sorry for being kind of slow here.  It's fine: there's a "From:" in
> >>> the patch, and git picks those up so it'll match the signed-off-by
> >>> line.  I send pretty much all my patches that way, as I never managed
> >>> to get my Google address working correctly.
> >>>
> >>>> Thanks,
> >>>>
> >>>> Alex
> >>>>
> >>>> On 10/9/21 7:12 PM, Alexandre Ghiti wrote:
> >>>>> From: Alexandre Ghiti <alex@ghiti.fr>
> >>>>>
> >>>>> This config allows to compile 64b kernel as PIE and to relocate it at
> >>>>> any virtual address at runtime: this paves the way to KASLR.
> >>>>> Runtime relocation is possible since relocation metadata are
> >>>>> embedded into
> >>>>> the kernel.
> >>> IMO this should really be user selectable, at a bare minimum so it's
> >>> testable.
> >>> I just sent along a patch to do that (my power's off at home, so email
> >>> is a bit
> >>> wacky right now).
> >>>
> >>> I haven't put this on for-next yet as I'm not sure if you had a fix
> >>> for the
> >>> kasan issue (which IIUC would conflict with this).
> >>
> >> The kasan issue only revealed that I need to move the kasan shadow
> >> memory around with sv48 support, that's not related to the relocatable
> >> kernel.
> >>
> >> Thanks,
> >>
> >> Alex
> >>
> >>
> >>>>> Note that relocating at runtime introduces an overhead even if the
> >>>>> kernel is loaded at the same address it was linked at and that the
> >>>>> compiler
> >>>>> options are those used in arm64 which uses the same RELA relocation
> >>>>> format.
> >>>>>
> >>>>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> >>>>> ---
> >>>>>   arch/riscv/Kconfig              | 12 ++++++++
> >>>>>   arch/riscv/Makefile             |  7 +++--
> >>>>>   arch/riscv/kernel/vmlinux.lds.S |  6 ++++
> >>>>>   arch/riscv/mm/Makefile          |  4 +++
> >>>>>   arch/riscv/mm/init.c            | 54
> >>>>> ++++++++++++++++++++++++++++++++-
> >>>>>   5 files changed, 80 insertions(+), 3 deletions(-)
> >>>>>
> >>>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> >>>>> index ea16fa2dd768..043ba92559fa 100644
> >>>>> --- a/arch/riscv/Kconfig
> >>>>> +++ b/arch/riscv/Kconfig
> >>>>> @@ -213,6 +213,18 @@ config PGTABLE_LEVELS
> >>>>>   config LOCKDEP_SUPPORT
> >>>>>       def_bool y
> >>>>>
> >>>>> +config RELOCATABLE
> >>>>> +    bool
> >>>>> +    depends on MMU && 64BIT && !XIP_KERNEL
> >>>>> +    help
> >>>>> +          This builds a kernel as a Position Independent Executable
> >>>>> (PIE),
> >>>>> +          which retains all relocation metadata required to
> >>>>> relocate the
> >>>>> +          kernel binary at runtime to a different virtual address
> >>>>> than the
> >>>>> +          address it was linked at.
> >>>>> +          Since RISCV uses the RELA relocation format, this
> >>>>> requires a
> >>>>> +          relocation pass at runtime even if the kernel is loaded
> >>>>> at the
> >>>>> +          same address it was linked at.
> >>>>> +
> >>>>>   source "arch/riscv/Kconfig.socs"
> >>>>>   source "arch/riscv/Kconfig.erratas"
> >>>>>
> >>>>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> >>>>> index 0eb4568fbd29..2f509915f246 100644
> >>>>> --- a/arch/riscv/Makefile
> >>>>> +++ b/arch/riscv/Makefile
> >>>>> @@ -9,9 +9,12 @@
> >>>>>   #
> >>>>>
> >>>>>   OBJCOPYFLAGS    := -O binary
> >>>>> -LDFLAGS_vmlinux :=
> >>>>> +ifeq ($(CONFIG_RELOCATABLE),y)
> >>>>> +    LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro
> >>>>> +    KBUILD_CFLAGS += -fPIE
> >>>>> +endif
> >>>>>   ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
> >>>>> -    LDFLAGS_vmlinux := --no-relax
> >>>>> +    LDFLAGS_vmlinux += --no-relax
> >>>>>       KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
> >>>>>       CC_FLAGS_FTRACE := -fpatchable-function-entry=8
> >>>>>   endif
> >>>>> diff --git a/arch/riscv/kernel/vmlinux.lds.S
> >>>>> b/arch/riscv/kernel/vmlinux.lds.S
> >>>>> index 5104f3a871e3..862a8c09723c 100644
> >>>>> --- a/arch/riscv/kernel/vmlinux.lds.S
> >>>>> +++ b/arch/riscv/kernel/vmlinux.lds.S
> >>>>> @@ -133,6 +133,12 @@ SECTIONS
> >>>>>
> >>>>>       BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
> >>>>>
> >>>>> +    .rela.dyn : ALIGN(8) {
> >>>>> +        __rela_dyn_start = .;
> >>>>> +        *(.rela .rela*)
> >>>>> +        __rela_dyn_end = .;
> >>>>> +    }
> >>>>> +
> >>>>>   #ifdef CONFIG_EFI
> >>>>>       . = ALIGN(PECOFF_SECTION_ALIGNMENT);
> >>>>>       __pecoff_data_virt_size = ABSOLUTE(. - __pecoff_text_end);
> >>>>> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> >>>>> index 7ebaef10ea1b..2d33ec574bbb 100644
> >>>>> --- a/arch/riscv/mm/Makefile
> >>>>> +++ b/arch/riscv/mm/Makefile
> >>>>> @@ -1,6 +1,10 @@
> >>>>>   # SPDX-License-Identifier: GPL-2.0-only
> >>>>>
> >>>>>   CFLAGS_init.o := -mcmodel=medany
> >>>>> +ifdef CONFIG_RELOCATABLE
> >>>>> +CFLAGS_init.o += -fno-pie
> >>>>> +endif
> >>>>> +
> >>>>>   ifdef CONFIG_FTRACE
> >>>>>   CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
> >>>>>   CFLAGS_REMOVE_cacheflush.o = $(CC_FLAGS_FTRACE)
> >>>>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> >>>>> index c0cddf0fc22d..42041c12d496 100644
> >>>>> --- a/arch/riscv/mm/init.c
> >>>>> +++ b/arch/riscv/mm/init.c
> >>>>> @@ -20,6 +20,9 @@
> >>>>>   #include <linux/dma-map-ops.h>
> >>>>>   #include <linux/crash_dump.h>
> >>>>>   #include <linux/hugetlb.h>
> >>>>> +#ifdef CONFIG_RELOCATABLE
> >>>>> +#include <linux/elf.h>
> >>>>> +#endif
> >>>>>
> >>>>>   #include <asm/fixmap.h>
> >>>>>   #include <asm/tlbflush.h>
> >>>>> @@ -103,7 +106,7 @@ static void __init print_vm_layout(void)
> >>>>>       print_mlm("lowmem", (unsigned long)PAGE_OFFSET,
> >>>>>             (unsigned long)high_memory);
> >>>>>   #ifdef CONFIG_64BIT
> >>>>> -    print_mlm("kernel", (unsigned long)KERNEL_LINK_ADDR,
> >>>>> +    print_mlm("kernel", (unsigned long)kernel_map.virt_addr,
> >>>>>             (unsigned long)ADDRESS_SPACE_END);
> >>>>>   #endif
> >>>>>   }
> >>>>> @@ -518,6 +521,44 @@ static __init pgprot_t pgprot_from_va(uintptr_t
> >>>>> va)
> >>>>>   #error "setup_vm() is called from head.S before relocate so it
> >>>>> should not use absolute addressing."
> >>>>>   #endif
> >>>>>
> >>>>> +#ifdef CONFIG_RELOCATABLE
> >>>>> +extern unsigned long __rela_dyn_start, __rela_dyn_end;
> >>>>> +
> >>>>> +static void __init relocate_kernel(void)
> >>>>> +{
> >>>>> +    Elf64_Rela *rela = (Elf64_Rela *)&__rela_dyn_start;
> >>>>> +    /*
> >>>>> +     * This holds the offset between the linked virtual address and
> >>>>> the
> >>>>> +     * relocated virtual address.
> >>>>> +     */
> >>>>> +    uintptr_t reloc_offset = kernel_map.virt_addr -
> >>>>> KERNEL_LINK_ADDR;
> >>>>> +    /*
> >>>>> +     * This holds the offset between kernel linked virtual
> >>>>> address and
> >>>>> +     * physical address.
> >>>>> +     */
> >>>>> +    uintptr_t va_kernel_link_pa_offset = KERNEL_LINK_ADDR -
> >>>>> kernel_map.phys_addr;
> >>>>> +
> >>>>> +    for ( ; rela < (Elf64_Rela *)&__rela_dyn_end; rela++) {
> >>>>> +        Elf64_Addr addr = (rela->r_offset -
> >>>>> va_kernel_link_pa_offset);
> >>>>> +        Elf64_Addr relocated_addr = rela->r_addend;
> >>>>> +
> >>>>> +        if (rela->r_info != R_RISCV_RELATIVE)
> >>>>> +            continue;
> >>>>> +
> >>>>> +        /*
> >>>>> +         * Make sure to not relocate vdso symbols like rt_sigreturn
> >>>>> +         * which are linked from the address 0 in vmlinux since
> >>>>> +         * vdso symbol addresses are actually used as an offset from
> >>>>> +         * mm->context.vdso in VDSO_OFFSET macro.
> >>>>> +         */
> >>>>> +        if (relocated_addr >= KERNEL_LINK_ADDR)
> >>>>> +            relocated_addr += reloc_offset;
> >>>>> +
> >>>>> +        *(Elf64_Addr *)addr = relocated_addr;
> >>>>> +    }
> >>>>> +}
> >>>>> +#endif /* CONFIG_RELOCATABLE */
> >>>>> +
> >>>>>   #ifdef CONFIG_XIP_KERNEL
> >>>>>   static void __init create_kernel_page_table(pgd_t *pgdir,
> >>>>>                           __always_unused bool early)
> >>>>> @@ -625,6 +666,17 @@ asmlinkage void __init setup_vm(uintptr_t
> >>>>> dtb_pa)
> >>>>>       BUG_ON((kernel_map.virt_addr + kernel_map.size) >
> >>>>> ADDRESS_SPACE_END - SZ_4K);
> >>>>>   #endif
> >>>>>
> >>>>> +#ifdef CONFIG_RELOCATABLE
> >>>>> +    /*
> >>>>> +     * Early page table uses only one PGDIR, which makes it possible
> >>>>> +     * to map PGDIR_SIZE aligned on PGDIR_SIZE: if the relocation
> >>>>> offset
> >>>>> +     * makes the kernel cross over a PGDIR_SIZE boundary, raise a
> >>>>> bug
> >>>>> +     * since a part of the kernel would not get mapped.
> >>>>> +     */
> >>>>> +    BUG_ON(PGDIR_SIZE - (kernel_map.virt_addr & (PGDIR_SIZE - 1)) <
> >>>>> kernel_map.size);
> >>>>> +    relocate_kernel();
> >>>>> +#endif
> >>>>> +
> >>>>>       pt_ops.alloc_pte = alloc_pte_early;
> >>>>>       pt_ops.get_pte_virt = get_pte_virt_early;
> >>>>>   #ifndef __PAGETABLE_PMD_FOLDED
> >
> > _______________________________________________
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