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From: Sedat Dilek <sedat.dilek@gmail.com>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Nick Desaulniers <ndesaulniers@google.com>,
	Fangrui Song <maskray@google.com>,
	Dmitry Golovin <dima@golovin.in>,
	Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Daniel Kiper <daniel.kiper@oracle.com>,
	Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>, "H . J . Lu" <hjl@sourceware.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 0/7] x86/boot: Remove run-time relocations from compressed kernel
Date: Wed, 15 Jul 2020 03:46:58 +0200	[thread overview]
Message-ID: <CA+icZUU7xXgDSc4ApF2ffyDCygu_N42tP6iF-XAvJAAVrD_B9A@mail.gmail.com> (raw)
In-Reply-To: <20200715004133.1430068-1-nivedita@alum.mit.edu>

On Wed, Jul 15, 2020 at 2:41 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> The compressed kernel currently contains bogus run-time relocations in
> the startup code in head_{32,64}.S, which are generated by the linker,
> but must not actually be processed at run-time.
>
> This generates warnings when linking with the BFD linker, and errors
> with LLD, which defaults to erroring on run-time relocations in read-only
> sections. It also requires the -z noreloc-overflow hack for the 64-bit
> kernel, which prevents us from linking it as -pie on an older BFD linker
> (<= 2.26) or on LLD, because the locations that are to be apparently
> relocated are only 32-bits in size and so cannot really have
> R_X86_64_RELATIVE relocations.
>
> This series aims to get rid of these relocations. I've build- and
> boot-tested with combinations of clang/gcc-10 with lld/bfd-2.34, and
> gcc-4.9.0 with bfd-2.24, skipping clang on 32-bit because it currently
> has other issues [0].
>
> The first three patches by Ard remove indirection via the GOT from the
> compressed kernel code.
>
> The next patch is an independent fix for LLD, to avoid an orphan
> section in arch/x86/boot/setup.elf.
>
> The fifth patch gets rid of almost all the relocations. It uses
> standard PIC addressing technique for 32-bit, i.e. loading a register
> with the address of _GLOBAL_OFFSET_TABLE_ and then using GOTOFF
> references to access variables. For 64-bit, there is 32-bit code that
> cannot use RIP-relative addressing, and also cannot use the 32-bit
> method, since GOTOFF references are 64-bit only. This is instead handled
> using a macro to replace a reference like gdt with (gdt-startup_32)
> instead. The assembler will generate a PC32 relocation entry, with
> addend set to (.-startup_32), and these will be replaced with constants
> at link time. This works as long as all the code using such references
> lives in the same section as startup_32, i.e. in .head.text.
>
> The sixth patch addresses a remaining issue with the BFD linker, which
> generates run-time relocations for absolute symbols. We use z_input_len
> and z_output_len, defined in the generated piggy.S file, as symbols
> whose absolute "addresses" are actually the size of the compressed
> payload and the size of the decompressed kernel image respectively. LLD
> does not generate relocations for these two symbols, but the BFD linker
> does, prior to the upcoming 2.35. To get around this, piggy.S is
> extended to also define two u32 variables (in .rodata) with the lengths,
> and the head code is modified to use those instead of the symbol
> addresses.
>
> An alternative way to handle z_input_len/z_output_len would be to just
> include piggy.S in head_{32,64}.S instead of as a separate object file,
> since the GNU assembler doesn't generate relocations for symbols set to
> constants.
>
> The last patch adds a check in the linker script to ensure that no
> run-time relocations get reintroduced.
>
> [0] https://lore.kernel.org/lkml/20200504230309.237398-1-ndesaulniers@google.com/
>
> Changes from v4:
> - Move -pie --no-dynamic-linker from KBUILD_LDFLAGS to LDFLAGS_vmlinux
>   Sedat: I'm not clear on whether you tested with the final LDFLAGS,
>   could you confirm: i.e. if you tested with -pie passed to LLD?
> - Replace runtime -> run-time to be consistent in wording
>

Hi Arvind,

thanks for v5.

With my diff applied against your patchset *v4*:

diff --git a/arch/x86/boot/compressed/Makefile
b/arch/x86/boot/compressed/Makefile
index 789d5d14d8b0..d0aafcd8cf6c 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -51,8 +51,8 @@ UBSAN_SANITIZE :=n
 KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
 # Compressed kernel should be built as PIE since it may be loaded at any
 # address by the bootloader.
-KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
-LDFLAGS_vmlinux := -T
+LDFLAGS_vmlinux := -pie $(call ld-option, --no-dynamic-linker)
+LDFLAGS_vmlinux += -T

 hostprogs      := mkpiggy
 HOST_EXTRACFLAGS += -I$(srctree)/tools/include

I was able to build/assemble with LLVM/Clang v11.0.0-git+ffee8040534
and boot on bare metal.

Note:
I have applied some additional patches to be compliant with LLVM_IAS=1
(Clang's Integrated Assembler) and LLVM=1 means LLVM utilities.
( As pointed out zstd-v7. )

- Sedat -

P.S.: Check my build-log

$ grep 'arch/x86/boot/compressed/vmlinux'
build-log_5.8.0-rc5-3-amd64-llvm11-ias.txt
make -f ./scripts/Makefile.build obj=arch/x86/boot/compressed
arch/x86/boot/compressed/vmlinux
  clang-11 -E -Wp,-MMD,arch/x86/boot/compressed/.vmlinux.lds.d
-nostdinc -isystem /usr/lib/llvm-11/lib/clang/11.0.0/include
-I./arch/x86/include -I./arch/x86/include/generated  -I./include
-I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi
-I./include/uapi -I./include/generated/uapi -include
./include/linux/kconfig.h -D__KERNEL__ -Qunused-arguments   -P -Ux86
-D__ASSEMBLY__ -DLINKER_SCRIPT -o arch/x86/boot/compressed/vmlinux.lds
arch/x86/boot/compressed/vmlinux.lds.S
  llvm-objcopy-11  -R .comment -S vmlinux arch/x86/boot/compressed/vmlinux.bin
  arch/x86/tools/relocs vmlinux >
arch/x86/boot/compressed/vmlinux.relocs;arch/x86/tools/relocs
--abs-relocs vmlinux
  { cat arch/x86/boot/compressed/vmlinux.bin
arch/x86/boot/compressed/vmlinux.relocs | zstd -22 --ultra; printf
\114\015\315\001; } > arch/x86/boot/compressed/vmlinux.bin.zst
  arch/x86/boot/compressed/mkpiggy
arch/x86/boot/compressed/vmlinux.bin.zst >
arch/x86/boot/compressed/piggy.S
  ld.lld-11 -m elf_x86_64  -pie  --no-dynamic-linker -T
arch/x86/boot/compressed/vmlinux.lds
arch/x86/boot/compressed/kernel_info.o
arch/x86/boot/compressed/head_64.o arch/x86/boot/compressed/misc.o
arch/x86/boot/compressed/string.o arch/x86/boot/compressed/cmdline.o
arch/x86/boot/compressed/error.o arch/x86/boot/compressed/piggy.o
arch/x86/boot/compressed/cpuflags.o
arch/x86/boot/compressed/early_serial_console.o
arch/x86/boot/compressed/kaslr.o arch/x86/boot/compressed/kaslr_64.o
arch/x86/boot/compressed/mem_encrypt.o
arch/x86/boot/compressed/pgtable_64.o arch/x86/boot/compressed/acpi.o
drivers/firmware/efi/libstub/lib.a
arch/x86/boot/compressed/efi_thunk_64.o -o
arch/x86/boot/compressed/vmlinux
  llvm-nm-11 arch/x86/boot/compressed/vmlinux | sed -n -e
's/^\([0-9a-fA-F]*\) [a-zA-Z]
\(startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|efi32_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|z_.*\)$/#define
ZO_ 0x/p' > arch/x86/boot/zoffset.h
  llvm-objcopy-11  -O binary -R .note -R .comment -S
arch/x86/boot/compressed/vmlinux arch/x86/boot/vmlinux.bin

- EOT -

> Changes from v3:
> - Move hidden.h to include/linux so the EFI stub and the compressed
>   kernel can share the same file
>
> Changes from v2:
> - Incorporate Ard's patches for eliminating GOT references into this
>   series
> - Rebase on v5.8-rc3
>
> v2: https://lore.kernel.org/lkml/20200525225918.1624470-1-nivedita@alum.mit.edu/
>
> Changes from v1:
> - Add .text.* to setup.ld instead of just .text.startup
> - Rename the la() macro introduced in the second patch for 64-bit to
>   rva(), and rework the explanatory comment.
> - In the last patch, check both .rel.dyn and .rela.dyn, instead of just
>   one per arch.
>
> Ard Biesheuvel (3):
>   x86/boot/compressed: Move .got.plt entries out of the .got section
>   x86/boot/compressed: Force hidden visibility for all symbol references
>   x86/boot/compressed: Get rid of GOT fixup code
>
> Arvind Sankar (4):
>   x86/boot: Add .text.* to setup.ld
>   x86/boot: Remove run-time relocations from .head.text code
>   x86/boot: Remove run-time relocations from head_{32,64}.S
>   x86/boot: Check that there are no run-time relocations
>
>  arch/x86/boot/compressed/Makefile      |  39 +-----
>  arch/x86/boot/compressed/head_32.S     |  99 +++++----------
>  arch/x86/boot/compressed/head_64.S     | 165 ++++++++++---------------
>  arch/x86/boot/compressed/mkpiggy.c     |   6 +
>  arch/x86/boot/compressed/vmlinux.lds.S |  24 +++-
>  arch/x86/boot/setup.ld                 |   2 +-
>  drivers/firmware/efi/libstub/Makefile  |   2 +-
>  drivers/firmware/efi/libstub/hidden.h  |   6 -
>  include/linux/hidden.h                 |  19 +++
>  9 files changed, 153 insertions(+), 209 deletions(-)
>  delete mode 100644 drivers/firmware/efi/libstub/hidden.h
>  create mode 100644 include/linux/hidden.h
>
>
> base-commit: e9919e11e219eaa5e8041b7b1a196839143e9125
> --
> 2.26.2
>

  reply	other threads:[~2020-07-15  1:47 UTC|newest]

Thread overview: 113+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-29 14:09 [PATCH v3 0/7] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
2020-06-29 14:09 ` [PATCH v3 1/7] x86/boot/compressed: Move .got.plt entries out of the .got section Arvind Sankar
2020-06-29 15:48   ` Kees Cook
2020-06-29 15:50     ` Arvind Sankar
2020-06-29 15:51       ` Ard Biesheuvel
2020-06-29 16:10         ` Kees Cook
2020-06-29 14:09 ` [PATCH v3 2/7] x86/boot/compressed: Force hidden visibility for all symbol references Arvind Sankar
2020-06-29 15:50   ` Kees Cook
2020-07-14  9:20   ` Sedat Dilek
2020-07-14  9:47     ` Ard Biesheuvel
2020-06-29 14:09 ` [PATCH v3 3/7] x86/boot/compressed: Get rid of GOT fixup code Arvind Sankar
2020-06-29 15:53   ` Kees Cook
2020-06-29 14:09 ` [PATCH v3 4/7] x86/boot: Add .text.* to setup.ld Arvind Sankar
2020-06-29 15:55   ` Kees Cook
2020-06-29 14:09 ` [PATCH v3 5/7] x86/boot: Remove run-time relocations from .head.text code Arvind Sankar
2020-06-29 16:04   ` Kees Cook
2020-06-29 17:01     ` Arvind Sankar
2020-07-14 13:20   ` Sedat Dilek
2020-06-29 14:09 ` [PATCH v3 6/7] x86/boot: Remove runtime relocations from head_{32,64}.S Arvind Sankar
2020-06-29 16:06   ` Kees Cook
2020-06-29 16:52     ` Arvind Sankar
2020-06-29 14:09 ` [PATCH v3 7/7] x86/boot: Check that there are no runtime relocations Arvind Sankar
2020-06-29 16:09   ` Kees Cook
2020-06-29 16:11     ` Ard Biesheuvel
2020-06-29 16:20       ` Kees Cook
2020-06-29 16:56         ` Arvind Sankar
2020-06-29 17:37           ` Fangrui Song
2020-06-29 18:11             ` Ard Biesheuvel
2020-06-29 23:34               ` Fangrui Song
2020-06-30 16:26                 ` Ard Biesheuvel
2020-06-30 17:54                   ` Arvind Sankar
2020-06-30 22:00                     ` Fangrui Song
2020-06-30 23:27                       ` Arvind Sankar
2020-07-01  6:44                         ` Ard Biesheuvel
2020-07-01 14:42                           ` Arvind Sankar
2020-06-29 18:43         ` Arvind Sankar
2020-07-14  2:38 ` [PATCH v4 0/7] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
2020-07-14 13:15   ` Sedat Dilek
2020-07-14 14:15     ` Arvind Sankar
2020-07-14 18:13       ` Sedat Dilek
2020-07-14 18:30         ` Sedat Dilek
2020-07-14 18:33           ` Sedat Dilek
2020-07-14 19:21             ` Sedat Dilek
2020-07-14 19:29           ` Arvind Sankar
2020-07-14 19:53             ` Sedat Dilek
2020-07-14 20:07               ` Arvind Sankar
2020-07-14 20:10                 ` Sedat Dilek
2020-07-14 20:14                   ` Arvind Sankar
2020-07-14 20:17                     ` Sedat Dilek
2020-07-14 20:08               ` Sedat Dilek
2020-07-14 20:21                 ` Arvind Sankar
2020-07-14 20:24                   ` Sedat Dilek
2020-07-14 20:27                     ` Sedat Dilek
2020-07-14 20:35                       ` Arvind Sankar
2020-07-14 20:43                         ` Sedat Dilek
2020-07-14 21:07                           ` Arvind Sankar
2020-07-14 20:33                     ` Arvind Sankar
2020-07-15  0:41   ` [PATCH v5 0/7] x86/boot: Remove run-time " Arvind Sankar
2020-07-15  1:46     ` Sedat Dilek [this message]
2020-07-15  7:11       ` Sedat Dilek
2020-07-17 13:46     ` Arvind Sankar
2020-07-17 18:16       ` Nick Desaulniers
2020-07-17 18:21         ` Sedat Dilek
2020-07-17 20:17         ` [PATCH-next " Arvind Sankar
2020-07-17 23:46           ` Nick Desaulniers
2020-07-29 22:04           ` Kees Cook
2020-07-29 22:23             ` Arvind Sankar
2020-07-30  2:38               ` Kees Cook
2020-07-17 20:17         ` [PATCH-next v5 1/7] x86/boot/compressed: Move .got.plt entries out of the .got section Arvind Sankar
2020-07-17 20:17         ` [PATCH-next v5 2/7] x86/boot/compressed: Force hidden visibility for all symbol references Arvind Sankar
2020-07-17 20:17         ` [PATCH-next v5 3/7] x86/boot/compressed: Get rid of GOT fixup code Arvind Sankar
2020-07-17 20:17         ` [PATCH-next v5 4/7] x86/boot: Add .text.* to setup.ld Arvind Sankar
2020-07-17 20:17         ` [PATCH-next v5 5/7] x86/boot: Remove run-time relocations from .head.text code Arvind Sankar
2020-07-17 20:18         ` [PATCH-next v5 6/7] x86/boot: Remove run-time relocations from head_{32,64}.S Arvind Sankar
2020-07-17 20:18         ` [PATCH-next v5 7/7] x86/boot: Check that there are no run-time relocations Arvind Sankar
2020-07-18  5:44         ` [PATCH v5 0/7] x86/boot: Remove run-time relocations from compressed kernel Ard Biesheuvel
2020-07-18  7:01           ` Sedat Dilek
2020-07-24 23:25           ` Kees Cook
2020-07-31 14:53             ` Arvind Sankar
2020-07-31 14:58               ` Sedat Dilek
2020-07-31 20:27                 ` [PATCH v6 " Arvind Sankar
2020-07-31 20:27                   ` [PATCH v6 1/7] x86/boot/compressed: Move .got.plt entries out of the .got section Arvind Sankar
2020-07-31 20:27                   ` [PATCH v6 2/7] x86/boot/compressed: Force hidden visibility for all symbol references Arvind Sankar
2020-07-31 20:27                   ` [PATCH v6 3/7] x86/boot/compressed: Get rid of GOT fixup code Arvind Sankar
2020-07-31 20:27                   ` [PATCH v6 4/7] x86/boot: Add .text.* to setup.ld Arvind Sankar
2020-07-31 20:27                   ` [PATCH v6 5/7] x86/boot: Remove run-time relocations from .head.text code Arvind Sankar
2020-07-31 20:27                   ` [PATCH v6 6/7] x86/boot: Remove run-time relocations from head_{32,64}.S Arvind Sankar
2020-07-31 20:27                   ` [PATCH v6 7/7] x86/boot: Check that there are no run-time relocations Arvind Sankar
2020-07-31 23:15                   ` [PATCH v6 0/7] x86/boot: Remove run-time relocations from compressed kernel Kees Cook
2020-07-15  0:41   ` [PATCH v5 1/7] x86/boot/compressed: Move .got.plt entries out of the .got section Arvind Sankar
2020-07-15  8:52     ` Sedat Dilek
2020-07-15  0:41   ` [PATCH v5 2/7] x86/boot/compressed: Force hidden visibility for all symbol references Arvind Sankar
2020-07-15  8:54     ` Sedat Dilek
2020-07-15  0:41   ` [PATCH v5 3/7] x86/boot/compressed: Get rid of GOT fixup code Arvind Sankar
2020-07-15  8:54     ` Sedat Dilek
2020-07-15  0:41   ` [PATCH v5 4/7] x86/boot: Add .text.* to setup.ld Arvind Sankar
2020-07-15  8:55     ` Sedat Dilek
2020-07-15  0:41   ` [PATCH v5 5/7] x86/boot: Remove run-time relocations from .head.text code Arvind Sankar
2020-07-15  8:56     ` Sedat Dilek
2020-07-15  0:41   ` [PATCH v5 6/7] x86/boot: Remove run-time relocations from head_{32,64}.S Arvind Sankar
2020-07-15  8:58     ` Sedat Dilek
2020-07-15  9:03       ` Ard Biesheuvel
2020-07-15  9:10         ` Sedat Dilek
2020-07-15  0:41   ` [PATCH v5 7/7] x86/boot: Check that there are no run-time relocations Arvind Sankar
2020-07-15  9:00     ` Sedat Dilek
2020-07-15  9:12       ` Sedat Dilek
2020-07-14  2:38 ` [PATCH v4 1/7] x86/boot/compressed: Move .got.plt entries out of the .got section Arvind Sankar
2020-07-14  2:38 ` [PATCH v4 2/7] x86/boot/compressed: Force hidden visibility for all symbol references Arvind Sankar
2020-07-14  2:38 ` [PATCH v4 3/7] x86/boot/compressed: Get rid of GOT fixup code Arvind Sankar
2020-07-14  2:38 ` [PATCH v4 4/7] x86/boot: Add .text.* to setup.ld Arvind Sankar
2020-07-14  2:38 ` [PATCH v4 5/7] x86/boot: Remove run-time relocations from .head.text code Arvind Sankar
2020-07-14  2:38 ` [PATCH v4 6/7] x86/boot: Remove runtime relocations from head_{32,64}.S Arvind Sankar
2020-07-14  2:38 ` [PATCH v4 7/7] x86/boot: Check that there are no runtime relocations Arvind Sankar

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