* Re: [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-24 21:28 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
@ 2020-05-25 7:10 ` Ard Biesheuvel
2020-05-25 22:59 ` [PATCH v2 " Arvind Sankar
` (5 subsequent siblings)
6 siblings, 0 replies; 53+ messages in thread
From: Ard Biesheuvel @ 2020-05-25 7:10 UTC (permalink / raw)
To: Arvind Sankar, Ingo Molnar, Borislav Petkov
Cc: Thomas Gleixner, H. Peter Anvin, X86 ML, Nick Desaulniers,
Fangrui Song, Dmitry Golovin, clang-built-linux, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Sun, 24 May 2020 at 23:28, Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> The compressed kernel currently contains bogus runtime relocations in
> the startup code in head_{32,64}.S, which are generated by the linker,
> but must not actually be processed at runtime.
>
> This generates warnings when linking with the BFD linker, and errors
> with LLD, which defaults to erroring on runtime 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 normally have
> R_X86_64_RELATIVE relocations.
>
> This series aims to get rid of these relocations. It is based on
> efi/next (efi-changes-for-v5.8), where the latest patches touch the
> head code to eliminate the global offset table.
>
Note: I dropped my decompressor linker script changes from that tag,
but they are still at the top of the efi/next branch.
Given these changes to go on top, I think it is better to merge all of
them separately, and let the x86 maintainers decide how and when.
(I can prepare a branch and a separate PR if desired)
For the series (modulo one nit in a separate reply)
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
> The first patch is an independent fix for LLD, to avoid an orphan
> section in arch/x86/boot/setup.elf [0].
>
> The second 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 third patch addresses a remaining issue with the BFD linker, which
> insists on generating runtime 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. 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
> runtime relocations get reintroduced. Since the GOT has been eliminated
> as well, the compressed kernel has no runtime relocations whatsoever any
> more.
>
> [0] https://lore.kernel.org/lkml/20200521152459.558081-1-nivedita@alum.mit.edu/
>
> Arvind Sankar (4):
> x86/boot: Add .text.startup to setup.ld
> x86/boot: Remove runtime relocations from .head.text code
> x86/boot: Remove runtime relocations from head_{32,64}.S
> x86/boot: Check that there are no runtime relocations
>
> arch/x86/boot/compressed/Makefile | 36 +---------
> arch/x86/boot/compressed/head_32.S | 59 +++++++--------
> arch/x86/boot/compressed/head_64.S | 99 +++++++++++++++-----------
> arch/x86/boot/compressed/mkpiggy.c | 6 ++
> arch/x86/boot/compressed/vmlinux.lds.S | 11 +++
> arch/x86/boot/setup.ld | 2 +-
> 6 files changed, 109 insertions(+), 104 deletions(-)
>
> --
> 2.26.2
>
^ permalink raw reply [flat|nested] 53+ messages in thread* [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-24 21:28 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
2020-05-25 7:10 ` Ard Biesheuvel
@ 2020-05-25 22:59 ` Arvind Sankar
2020-05-26 12:29 ` Sedat Dilek
2020-05-25 22:59 ` [PATCH v2 1/4] x86/boot: Add .text.* to setup.ld Arvind Sankar
` (4 subsequent siblings)
6 siblings, 1 reply; 53+ messages in thread
From: Arvind Sankar @ 2020-05-25 22:59 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, Borislav Petkov, H. Peter Anvin, x86
Cc: Nick Desaulniers, Fangrui Song, Dmitry Golovin,
clang-built-linux, Ard Biesheuvel, Masahiro Yamada, Daniel Kiper,
linux-kernel
The compressed kernel currently contains bogus runtime relocations in
the startup code in head_{32,64}.S, which are generated by the linker,
but must not actually be processed at runtime.
This generates warnings when linking with the BFD linker, and errors
with LLD, which defaults to erroring on runtime 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 normally have
R_X86_64_RELATIVE relocations.
This series aims to get rid of these relocations. It is based on
efi/next, where the latest patches touch the head code to eliminate the
global offset table.
The first patch is an independent fix for LLD, to avoid an orphan
section in arch/x86/boot/setup.elf.
The second 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 third patch addresses a remaining issue with the BFD linker, which
insists on generating runtime 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
runtime relocations get reintroduced. Since the GOT has been eliminated
as well, the compressed kernel has no runtime relocations whatsoever any
more.
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.
Arvind Sankar (4):
x86/boot: Add .text.* to setup.ld
x86/boot: Remove run-time relocations from .head.text code
x86/boot: Remove runtime relocations from head_{32,64}.S
x86/boot: Check that there are no runtime relocations
arch/x86/boot/compressed/Makefile | 36 +--------
arch/x86/boot/compressed/head_32.S | 59 +++++++-------
arch/x86/boot/compressed/head_64.S | 108 +++++++++++++++----------
arch/x86/boot/compressed/mkpiggy.c | 6 ++
arch/x86/boot/compressed/vmlinux.lds.S | 8 ++
arch/x86/boot/setup.ld | 2 +-
6 files changed, 115 insertions(+), 104 deletions(-)
--
2.26.2
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-25 22:59 ` [PATCH v2 " Arvind Sankar
@ 2020-05-26 12:29 ` Sedat Dilek
2020-05-26 12:30 ` Ard Biesheuvel
0 siblings, 1 reply; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 12:29 UTC (permalink / raw)
To: Arvind Sankar
Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, H. Peter Anvin,
x86, Nick Desaulniers, Fangrui Song, Dmitry Golovin,
Clang-Built-Linux ML, Ard Biesheuvel, Masahiro Yamada,
Daniel Kiper, linux-kernel
On Tue, May 26, 2020 at 12:59 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> The compressed kernel currently contains bogus runtime relocations in
> the startup code in head_{32,64}.S, which are generated by the linker,
> but must not actually be processed at runtime.
>
> This generates warnings when linking with the BFD linker, and errors
> with LLD, which defaults to erroring on runtime 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 normally have
> R_X86_64_RELATIVE relocations.
>
> This series aims to get rid of these relocations. It is based on
> efi/next, where the latest patches touch the head code to eliminate the
> global offset table.
>
> The first patch is an independent fix for LLD, to avoid an orphan
> section in arch/x86/boot/setup.elf.
>
> The second 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 third patch addresses a remaining issue with the BFD linker, which
> insists on generating runtime 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
> runtime relocations get reintroduced. Since the GOT has been eliminated
> as well, the compressed kernel has no runtime relocations whatsoever any
> more.
>
> 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.
>
Hi,
I would like to test this patchset v2 on top of Linux v5.7-rc7 together with:
[1] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux
[2] x86/boot: Correct relocation destination on old linkers
I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the
merge problems, but I am not sure I did it correctly.
So, which patches are really relevant from efi/next?
What's your suggestions?
Regards,
- Sedat -
[1] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/patch/?id=d6ee6529436a15a0541aff6e1697989ee7dc2c44
[2] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/patch/?id=5214028dd89e49ba27007c3ee475279e584261f0
> Arvind Sankar (4):
> x86/boot: Add .text.* to setup.ld
> x86/boot: Remove run-time relocations from .head.text code
> x86/boot: Remove runtime relocations from head_{32,64}.S
> x86/boot: Check that there are no runtime relocations
>
> arch/x86/boot/compressed/Makefile | 36 +--------
> arch/x86/boot/compressed/head_32.S | 59 +++++++-------
> arch/x86/boot/compressed/head_64.S | 108 +++++++++++++++----------
> arch/x86/boot/compressed/mkpiggy.c | 6 ++
> arch/x86/boot/compressed/vmlinux.lds.S | 8 ++
> arch/x86/boot/setup.ld | 2 +-
> 6 files changed, 115 insertions(+), 104 deletions(-)
>
> --
> 2.26.2
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200525225918.1624470-1-nivedita%40alum.mit.edu.
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 12:29 ` Sedat Dilek
@ 2020-05-26 12:30 ` Ard Biesheuvel
2020-05-26 12:33 ` Sedat Dilek
0 siblings, 1 reply; 53+ messages in thread
From: Ard Biesheuvel @ 2020-05-26 12:30 UTC (permalink / raw)
To: sedat.dilek
Cc: Arvind Sankar, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, 26 May 2020 at 14:29, Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Tue, May 26, 2020 at 12:59 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > The compressed kernel currently contains bogus runtime relocations in
> > the startup code in head_{32,64}.S, which are generated by the linker,
> > but must not actually be processed at runtime.
> >
> > This generates warnings when linking with the BFD linker, and errors
> > with LLD, which defaults to erroring on runtime 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 normally have
> > R_X86_64_RELATIVE relocations.
> >
> > This series aims to get rid of these relocations. It is based on
> > efi/next, where the latest patches touch the head code to eliminate the
> > global offset table.
> >
> > The first patch is an independent fix for LLD, to avoid an orphan
> > section in arch/x86/boot/setup.elf.
> >
> > The second 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 third patch addresses a remaining issue with the BFD linker, which
> > insists on generating runtime 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
> > runtime relocations get reintroduced. Since the GOT has been eliminated
> > as well, the compressed kernel has no runtime relocations whatsoever any
> > more.
> >
> > 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.
> >
>
> Hi,
>
> I would like to test this patchset v2 on top of Linux v5.7-rc7 together with:
>
> [1] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux
> [2] x86/boot: Correct relocation destination on old linkers
>
> I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the
> merge problems, but I am not sure I did it correctly.
> So, which patches are really relevant from efi/next?
>
> What's your suggestions?
>
efi/next is here:
https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/log/?h=next
You'll need the top 3 patches.
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 12:30 ` Ard Biesheuvel
@ 2020-05-26 12:33 ` Sedat Dilek
2020-05-26 12:44 ` Sedat Dilek
0 siblings, 1 reply; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 12:33 UTC (permalink / raw)
To: Ard Biesheuvel
Cc: Arvind Sankar, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 2:30 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Tue, 26 May 2020 at 14:29, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > On Tue, May 26, 2020 at 12:59 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >
> > > The compressed kernel currently contains bogus runtime relocations in
> > > the startup code in head_{32,64}.S, which are generated by the linker,
> > > but must not actually be processed at runtime.
> > >
> > > This generates warnings when linking with the BFD linker, and errors
> > > with LLD, which defaults to erroring on runtime 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 normally have
> > > R_X86_64_RELATIVE relocations.
> > >
> > > This series aims to get rid of these relocations. It is based on
> > > efi/next, where the latest patches touch the head code to eliminate the
> > > global offset table.
> > >
> > > The first patch is an independent fix for LLD, to avoid an orphan
> > > section in arch/x86/boot/setup.elf.
> > >
> > > The second 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 third patch addresses a remaining issue with the BFD linker, which
> > > insists on generating runtime 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
> > > runtime relocations get reintroduced. Since the GOT has been eliminated
> > > as well, the compressed kernel has no runtime relocations whatsoever any
> > > more.
> > >
> > > 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.
> > >
> >
> > Hi,
> >
> > I would like to test this patchset v2 on top of Linux v5.7-rc7 together with:
> >
> > [1] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux
> > [2] x86/boot: Correct relocation destination on old linkers
> >
> > I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the
> > merge problems, but I am not sure I did it correctly.
> > So, which patches are really relevant from efi/next?
> >
> > What's your suggestions?
> >
>
> efi/next is here:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/log/?h=next
>
> You'll need the top 3 patches.
Thanks /o\.
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 12:33 ` Sedat Dilek
@ 2020-05-26 12:44 ` Sedat Dilek
2020-05-26 14:47 ` Arvind Sankar
2020-05-26 14:48 ` Sedat Dilek
0 siblings, 2 replies; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 12:44 UTC (permalink / raw)
To: Ard Biesheuvel
Cc: Arvind Sankar, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 2:33 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Tue, May 26, 2020 at 2:30 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Tue, 26 May 2020 at 14:29, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > >
> > > On Tue, May 26, 2020 at 12:59 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > > >
> > > > The compressed kernel currently contains bogus runtime relocations in
> > > > the startup code in head_{32,64}.S, which are generated by the linker,
> > > > but must not actually be processed at runtime.
> > > >
> > > > This generates warnings when linking with the BFD linker, and errors
> > > > with LLD, which defaults to erroring on runtime 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 normally have
> > > > R_X86_64_RELATIVE relocations.
> > > >
> > > > This series aims to get rid of these relocations. It is based on
> > > > efi/next, where the latest patches touch the head code to eliminate the
> > > > global offset table.
> > > >
> > > > The first patch is an independent fix for LLD, to avoid an orphan
> > > > section in arch/x86/boot/setup.elf.
> > > >
> > > > The second 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 third patch addresses a remaining issue with the BFD linker, which
> > > > insists on generating runtime 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
> > > > runtime relocations get reintroduced. Since the GOT has been eliminated
> > > > as well, the compressed kernel has no runtime relocations whatsoever any
> > > > more.
> > > >
> > > > 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.
> > > >
> > >
> > > Hi,
> > >
> > > I would like to test this patchset v2 on top of Linux v5.7-rc7 together with:
> > >
> > > [1] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux
> > > [2] x86/boot: Correct relocation destination on old linkers
> > >
> > > I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the
> > > merge problems, but I am not sure I did it correctly.
> > > So, which patches are really relevant from efi/next?
> > >
> > > What's your suggestions?
> > >
> >
> > efi/next is here:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/log/?h=next
> >
> > You'll need the top 3 patches.
>
> Thanks /o\.
>
> - Sedat -
Are those diffs correct when using "x86/boot: Correct relocation
destination on old linkers"?
$ cat ../head_32_S.diff
diff --cc arch/x86/boot/compressed/head_32.S
index 064e895bad92,03557f2174bf..000000000000
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@@ -49,13 -49,17 +49,14 @@@
* Position Independent Executable (PIE) so that linker won't optimize
* R_386_GOT32X relocation to its fixed symbol address. Older
* linkers generate R_386_32 relocations against locally defined symbols,
- * _bss, _ebss, in PIE. It isn't wrong, just suboptimal compared
- * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less
- * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
++ * _bss, _ebss, _end in PIE. It isn't wrong, just suboptimal compared
+ * to R_386_RELATIVE. But the x86 kernel fails to properly handle
* R_386_32 relocations when relocating the kernel. To generate
- * R_386_RELATIVE relocations, we mark _bss and _ebss as hidden:
- * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as
- * hidden:
++ * R_386_RELATIVE relocations, we mark _bss, _ebss and _end as hidden:
*/
.hidden _bss
.hidden _ebss
- .hidden _got
- .hidden _egot
+ .hidden _end
__HEAD
SYM_FUNC_START(startup_32)
$ cat ../head_64_S.diff
diff --cc arch/x86/boot/compressed/head_64.S
index 4b7ad1dfbea6,76d1d64d51e3..000000000000
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@@ -40,34 -40,11 +40,35 @@@
*/
.hidden _bss
.hidden _ebss
- .hidden _got
- .hidden _egot
+ .hidden _end
__HEAD
+
+/*
+ * This macro gives the relative virtual address of X, i.e. the offset of X
+ * from startup_32. This is the same as the link-time virtual address of X,
+ * since startup_32 is at 0, but defining it this way tells the
+ * assembler/linker that we do not want the actual run-time address of X. This
+ * prevents the linker from trying to create unwanted run-time relocation
+ * entries for the reference when the compressed kernel is linked as PIE.
+ *
+ * A reference X(%reg) will result in the link-time VA of X being stored with
+ * the instruction, and a run-time R_X86_64_RELATIVE relocation entry that
+ * adds the 64-bit base address where the kernel is loaded.
+ *
+ * Replacing it with (X-startup_32)(%reg) results in the offset being stored,
+ * and no run-time relocation.
+ *
+ * The macro should be used as a displacement with a base register containing
+ * the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an immediate
+ * [$ rva(X)].
+ *
+ * This macro can only be used from within the .head.text section, since the
+ * expression requires startup_32 to be in the same section as the code being
+ * assembled.
+ */
+#define rva(X) ((X) - startup_32)
+
.code32
SYM_FUNC_START(startup_32)
/*
Thanks.
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 12:44 ` Sedat Dilek
@ 2020-05-26 14:47 ` Arvind Sankar
2020-05-26 14:50 ` Sedat Dilek
2020-05-26 14:48 ` Sedat Dilek
1 sibling, 1 reply; 53+ messages in thread
From: Arvind Sankar @ 2020-05-26 14:47 UTC (permalink / raw)
To: Sedat Dilek
Cc: Ard Biesheuvel, Arvind Sankar, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, H. Peter Anvin, X86 ML, Nick Desaulniers,
Fangrui Song, Dmitry Golovin, Clang-Built-Linux ML,
Masahiro Yamada, Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 02:44:29PM +0200, Sedat Dilek wrote:
>
> Are those diffs correct when using "x86/boot: Correct relocation
> destination on old linkers"?
>
It looks ok, but that patch (and even marking the other symbols .hidden)
should be unnecessary after this series.
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 14:47 ` Arvind Sankar
@ 2020-05-26 14:50 ` Sedat Dilek
2020-05-26 15:36 ` Arvind Sankar
0 siblings, 1 reply; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 14:50 UTC (permalink / raw)
To: Arvind Sankar
Cc: Ard Biesheuvel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 4:47 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> On Tue, May 26, 2020 at 02:44:29PM +0200, Sedat Dilek wrote:
> >
> > Are those diffs correct when using "x86/boot: Correct relocation
> > destination on old linkers"?
> >
>
> It looks ok, but that patch (and even marking the other symbols .hidden)
> should be unnecessary after this series.
You mean _bss, _ebss and _end?
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 14:50 ` Sedat Dilek
@ 2020-05-26 15:36 ` Arvind Sankar
2020-05-26 15:38 ` Sedat Dilek
2020-05-27 6:26 ` Sedat Dilek
0 siblings, 2 replies; 53+ messages in thread
From: Arvind Sankar @ 2020-05-26 15:36 UTC (permalink / raw)
To: Sedat Dilek
Cc: Arvind Sankar, Ard Biesheuvel, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, H. Peter Anvin, X86 ML, Nick Desaulniers,
Fangrui Song, Dmitry Golovin, Clang-Built-Linux ML,
Masahiro Yamada, Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 04:50:38PM +0200, Sedat Dilek wrote:
> On Tue, May 26, 2020 at 4:47 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > On Tue, May 26, 2020 at 02:44:29PM +0200, Sedat Dilek wrote:
> > >
> > > Are those diffs correct when using "x86/boot: Correct relocation
> > > destination on old linkers"?
> > >
> >
> > It looks ok, but that patch (and even marking the other symbols .hidden)
> > should be unnecessary after this series.
>
> You mean _bss, _ebss and _end?
>
> - Sedat -
Yes. Those .hidden markings are there to ensure that when relocations
are generated (as they are currently), they're generated as
R_386_RELATIVE (which uses B+A calculation, with A being the link-time
virtual address of the symbol, and stored in the relocation field)
rather than R_386_32 (which uses S+A calculation, and so doesn't work
without runtime processing). After this patchset there aren't any
relocations, so while the .hidden markings won't hurt, they won't be
necessary either.
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 15:36 ` Arvind Sankar
@ 2020-05-26 15:38 ` Sedat Dilek
2020-05-27 6:26 ` Sedat Dilek
1 sibling, 0 replies; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 15:38 UTC (permalink / raw)
To: Arvind Sankar
Cc: Ard Biesheuvel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 5:36 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> On Tue, May 26, 2020 at 04:50:38PM +0200, Sedat Dilek wrote:
> > On Tue, May 26, 2020 at 4:47 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >
> > > On Tue, May 26, 2020 at 02:44:29PM +0200, Sedat Dilek wrote:
> > > >
> > > > Are those diffs correct when using "x86/boot: Correct relocation
> > > > destination on old linkers"?
> > > >
> > >
> > > It looks ok, but that patch (and even marking the other symbols .hidden)
> > > should be unnecessary after this series.
> >
> > You mean _bss, _ebss and _end?
> >
> > - Sedat -
>
> Yes. Those .hidden markings are there to ensure that when relocations
> are generated (as they are currently), they're generated as
> R_386_RELATIVE (which uses B+A calculation, with A being the link-time
> virtual address of the symbol, and stored in the relocation field)
> rather than R_386_32 (which uses S+A calculation, and so doesn't work
> without runtime processing). After this patchset there aren't any
> relocations, so while the .hidden markings won't hurt, they won't be
> necessary either.
>
So, I am here on Debian/testing AMD64.
How can I test the patchset worked correctly?
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 15:36 ` Arvind Sankar
2020-05-26 15:38 ` Sedat Dilek
@ 2020-05-27 6:26 ` Sedat Dilek
1 sibling, 0 replies; 53+ messages in thread
From: Sedat Dilek @ 2020-05-27 6:26 UTC (permalink / raw)
To: Arvind Sankar
Cc: Ard Biesheuvel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 5:36 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> On Tue, May 26, 2020 at 04:50:38PM +0200, Sedat Dilek wrote:
> > On Tue, May 26, 2020 at 4:47 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >
> > > On Tue, May 26, 2020 at 02:44:29PM +0200, Sedat Dilek wrote:
> > > >
> > > > Are those diffs correct when using "x86/boot: Correct relocation
> > > > destination on old linkers"?
> > > >
> > >
> > > It looks ok, but that patch (and even marking the other symbols .hidden)
> > > should be unnecessary after this series.
> >
> > You mean _bss, _ebss and _end?
> >
> > - Sedat -
>
> Yes. Those .hidden markings are there to ensure that when relocations
> are generated (as they are currently), they're generated as
> R_386_RELATIVE (which uses B+A calculation, with A being the link-time
> virtual address of the symbol, and stored in the relocation field)
> rather than R_386_32 (which uses S+A calculation, and so doesn't work
> without runtime processing). After this patchset there aren't any
> relocations, so while the .hidden markings won't hurt, they won't be
> necessary either.
>
Do you plan a change on this?
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 12:44 ` Sedat Dilek
2020-05-26 14:47 ` Arvind Sankar
@ 2020-05-26 14:48 ` Sedat Dilek
2020-05-26 14:55 ` Sedat Dilek
1 sibling, 1 reply; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 14:48 UTC (permalink / raw)
To: Ard Biesheuvel
Cc: Arvind Sankar, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 2:44 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Tue, May 26, 2020 at 2:33 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > On Tue, May 26, 2020 at 2:30 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > On Tue, 26 May 2020 at 14:29, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > > >
> > > > On Tue, May 26, 2020 at 12:59 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > > > >
> > > > > The compressed kernel currently contains bogus runtime relocations in
> > > > > the startup code in head_{32,64}.S, which are generated by the linker,
> > > > > but must not actually be processed at runtime.
> > > > >
> > > > > This generates warnings when linking with the BFD linker, and errors
> > > > > with LLD, which defaults to erroring on runtime 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 normally have
> > > > > R_X86_64_RELATIVE relocations.
> > > > >
> > > > > This series aims to get rid of these relocations. It is based on
> > > > > efi/next, where the latest patches touch the head code to eliminate the
> > > > > global offset table.
> > > > >
> > > > > The first patch is an independent fix for LLD, to avoid an orphan
> > > > > section in arch/x86/boot/setup.elf.
> > > > >
> > > > > The second 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 third patch addresses a remaining issue with the BFD linker, which
> > > > > insists on generating runtime 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
> > > > > runtime relocations get reintroduced. Since the GOT has been eliminated
> > > > > as well, the compressed kernel has no runtime relocations whatsoever any
> > > > > more.
> > > > >
> > > > > 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.
> > > > >
> > > >
> > > > Hi,
> > > >
> > > > I would like to test this patchset v2 on top of Linux v5.7-rc7 together with:
> > > >
> > > > [1] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux
> > > > [2] x86/boot: Correct relocation destination on old linkers
> > > >
> > > > I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the
> > > > merge problems, but I am not sure I did it correctly.
> > > > So, which patches are really relevant from efi/next?
> > > >
> > > > What's your suggestions?
> > > >
> > >
> > > efi/next is here:
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/log/?h=next
> > >
> > > You'll need the top 3 patches.
> >
> > Thanks /o\.
> >
> > - Sedat -
>
> Are those diffs correct when using "x86/boot: Correct relocation
> destination on old linkers"?
>
> $ cat ../head_32_S.diff
> diff --cc arch/x86/boot/compressed/head_32.S
> index 064e895bad92,03557f2174bf..000000000000
> --- a/arch/x86/boot/compressed/head_32.S
> +++ b/arch/x86/boot/compressed/head_32.S
> @@@ -49,13 -49,17 +49,14 @@@
> * Position Independent Executable (PIE) so that linker won't optimize
> * R_386_GOT32X relocation to its fixed symbol address. Older
> * linkers generate R_386_32 relocations against locally defined symbols,
> - * _bss, _ebss, in PIE. It isn't wrong, just suboptimal compared
> - * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less
> - * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
> ++ * _bss, _ebss, _end in PIE. It isn't wrong, just suboptimal compared
> + * to R_386_RELATIVE. But the x86 kernel fails to properly handle
> * R_386_32 relocations when relocating the kernel. To generate
> - * R_386_RELATIVE relocations, we mark _bss and _ebss as hidden:
> - * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as
> - * hidden:
> ++ * R_386_RELATIVE relocations, we mark _bss, _ebss and _end as hidden:
> */
> .hidden _bss
> .hidden _ebss
> - .hidden _got
> - .hidden _egot
> + .hidden _end
>
> __HEAD
> SYM_FUNC_START(startup_32)
>
> $ cat ../head_64_S.diff
> diff --cc arch/x86/boot/compressed/head_64.S
> index 4b7ad1dfbea6,76d1d64d51e3..000000000000
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@@ -40,34 -40,11 +40,35 @@@
> */
> .hidden _bss
> .hidden _ebss
> - .hidden _got
> - .hidden _egot
> + .hidden _end
>
> __HEAD
> +
> +/*
> + * This macro gives the relative virtual address of X, i.e. the offset of X
> + * from startup_32. This is the same as the link-time virtual address of X,
> + * since startup_32 is at 0, but defining it this way tells the
> + * assembler/linker that we do not want the actual run-time address of X. This
> + * prevents the linker from trying to create unwanted run-time relocation
> + * entries for the reference when the compressed kernel is linked as PIE.
> + *
> + * A reference X(%reg) will result in the link-time VA of X being stored with
> + * the instruction, and a run-time R_X86_64_RELATIVE relocation entry that
> + * adds the 64-bit base address where the kernel is loaded.
> + *
> + * Replacing it with (X-startup_32)(%reg) results in the offset being stored,
> + * and no run-time relocation.
> + *
> + * The macro should be used as a displacement with a base register containing
> + * the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an immediate
> + * [$ rva(X)].
> + *
> + * This macro can only be used from within the .head.text section, since the
> + * expression requires startup_32 to be in the same section as the code being
> + * assembled.
> + */
> +#define rva(X) ((X) - startup_32)
> +
> .code32
> SYM_FUNC_START(startup_32)
> /*
>
> Thanks.
>
With LLVM/Clang/LLD I see:
mycompiler -Wp,-MD,arch/x86/boot/compressed/.kernel_info.o.d
-nostdinc -isystem
/home/dileks/src/llvm-toolchain/install/lib/clang/10.0.1rc1/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 -m64 -O2
-fno-strict-aliasing -fPIE -DDISABLE_BRANCH_PROFILING -mcmodel=small
-mno-mmx -mno-sse -ffreestanding -fno-stack-protector
-Wno-address-of-packed-member -Wno-gnu -Wno-pointer-sign
-fmacro-prefix-map=./= -fno-asynchronous-unwind-tables -include
hidden.h -D__ASSEMBLY__ -c -o
arch/x86/boot/compressed/kernel_info.o
arch/x86/boot/compressed/kernel_info.S
<built-in>:345:10: fatal error: 'hidden.h' file not found
#include "hidden.h"
^~~~~~~~~~
1 error generated.
make[5]: *** [scripts/Makefile.build:349:
arch/x86/boot/compressed/kernel_info.o] Error 1
make[4]: *** [arch/x86/boot/Makefile:114:
arch/x86/boot/compressed/vmlinux] Error 2
make[4]: *** Waiting for unfinished jobs....
mycompiler is a wrapper-script to use ccache * clang-10 as compiler.
patchset to previous build:
$ git log --no-merges --oneline 5.7.0-rc7-1-amd64-clang..5.7.0-rc7-2-amd64-clang
8b74901cb9e5 (for-5.7/x86-boot-remove-runtime-relocations-from-compressed-kernel-v2-nivedita76)
x86/boot: Check that there are no runtime relocations
83fb1bc3b076 x86/boot: Remove runtime relocations from head_{32,64}.S
fede23dacbbd x86/boot: Remove run-time relocations from .head.text code
3e5ea481b8fb x86/boot: Add .text.* to setup.ld
bec910ba3d67 x86/boot/compressed: Get rid of GOT fixup code
be834cee6f39 x86/boot/compressed: Force hidden visibility for all
symbol references
9b7c7d8d2d7b x86/boot/compressed: Move .got.plt entries out of the .got section
ba6a49f806a0 (for-5.7/kbuild-compressed-debug-info) Makefile: support
compressed debug info
a1fb11944d11 (for-5.7/x86-boot-nivedita76) x86/boot: Correct
relocation destination on old linkers
c70e3890058f (for-5.7/x86-build-maskray) x86/boot: Discard
.discard.unreachable for arch/x86/boot/compressed/vmlinux
$ find ./ -name hidden.h
./drivers/firmware/efi/libstub/hidden.h
./arch/x86/boot/compressed/hidden.h
Any thoughts?
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 14:48 ` Sedat Dilek
@ 2020-05-26 14:55 ` Sedat Dilek
2020-05-26 15:07 ` Sedat Dilek
0 siblings, 1 reply; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 14:55 UTC (permalink / raw)
To: Ard Biesheuvel
Cc: Arvind Sankar, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 4:48 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Tue, May 26, 2020 at 2:44 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > On Tue, May 26, 2020 at 2:33 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > >
> > > On Tue, May 26, 2020 at 2:30 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> > > >
> > > > On Tue, 26 May 2020 at 14:29, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > > > >
> > > > > On Tue, May 26, 2020 at 12:59 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > > > > >
> > > > > > The compressed kernel currently contains bogus runtime relocations in
> > > > > > the startup code in head_{32,64}.S, which are generated by the linker,
> > > > > > but must not actually be processed at runtime.
> > > > > >
> > > > > > This generates warnings when linking with the BFD linker, and errors
> > > > > > with LLD, which defaults to erroring on runtime 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 normally have
> > > > > > R_X86_64_RELATIVE relocations.
> > > > > >
> > > > > > This series aims to get rid of these relocations. It is based on
> > > > > > efi/next, where the latest patches touch the head code to eliminate the
> > > > > > global offset table.
> > > > > >
> > > > > > The first patch is an independent fix for LLD, to avoid an orphan
> > > > > > section in arch/x86/boot/setup.elf.
> > > > > >
> > > > > > The second 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 third patch addresses a remaining issue with the BFD linker, which
> > > > > > insists on generating runtime 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
> > > > > > runtime relocations get reintroduced. Since the GOT has been eliminated
> > > > > > as well, the compressed kernel has no runtime relocations whatsoever any
> > > > > > more.
> > > > > >
> > > > > > 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.
> > > > > >
> > > > >
> > > > > Hi,
> > > > >
> > > > > I would like to test this patchset v2 on top of Linux v5.7-rc7 together with:
> > > > >
> > > > > [1] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux
> > > > > [2] x86/boot: Correct relocation destination on old linkers
> > > > >
> > > > > I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the
> > > > > merge problems, but I am not sure I did it correctly.
> > > > > So, which patches are really relevant from efi/next?
> > > > >
> > > > > What's your suggestions?
> > > > >
> > > >
> > > > efi/next is here:
> > > >
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/log/?h=next
> > > >
> > > > You'll need the top 3 patches.
> > >
> > > Thanks /o\.
> > >
> > > - Sedat -
> >
> > Are those diffs correct when using "x86/boot: Correct relocation
> > destination on old linkers"?
> >
> > $ cat ../head_32_S.diff
> > diff --cc arch/x86/boot/compressed/head_32.S
> > index 064e895bad92,03557f2174bf..000000000000
> > --- a/arch/x86/boot/compressed/head_32.S
> > +++ b/arch/x86/boot/compressed/head_32.S
> > @@@ -49,13 -49,17 +49,14 @@@
> > * Position Independent Executable (PIE) so that linker won't optimize
> > * R_386_GOT32X relocation to its fixed symbol address. Older
> > * linkers generate R_386_32 relocations against locally defined symbols,
> > - * _bss, _ebss, in PIE. It isn't wrong, just suboptimal compared
> > - * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less
> > - * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
> > ++ * _bss, _ebss, _end in PIE. It isn't wrong, just suboptimal compared
> > + * to R_386_RELATIVE. But the x86 kernel fails to properly handle
> > * R_386_32 relocations when relocating the kernel. To generate
> > - * R_386_RELATIVE relocations, we mark _bss and _ebss as hidden:
> > - * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as
> > - * hidden:
> > ++ * R_386_RELATIVE relocations, we mark _bss, _ebss and _end as hidden:
> > */
> > .hidden _bss
> > .hidden _ebss
> > - .hidden _got
> > - .hidden _egot
> > + .hidden _end
> >
> > __HEAD
> > SYM_FUNC_START(startup_32)
> >
> > $ cat ../head_64_S.diff
> > diff --cc arch/x86/boot/compressed/head_64.S
> > index 4b7ad1dfbea6,76d1d64d51e3..000000000000
> > --- a/arch/x86/boot/compressed/head_64.S
> > +++ b/arch/x86/boot/compressed/head_64.S
> > @@@ -40,34 -40,11 +40,35 @@@
> > */
> > .hidden _bss
> > .hidden _ebss
> > - .hidden _got
> > - .hidden _egot
> > + .hidden _end
> >
> > __HEAD
> > +
> > +/*
> > + * This macro gives the relative virtual address of X, i.e. the offset of X
> > + * from startup_32. This is the same as the link-time virtual address of X,
> > + * since startup_32 is at 0, but defining it this way tells the
> > + * assembler/linker that we do not want the actual run-time address of X. This
> > + * prevents the linker from trying to create unwanted run-time relocation
> > + * entries for the reference when the compressed kernel is linked as PIE.
> > + *
> > + * A reference X(%reg) will result in the link-time VA of X being stored with
> > + * the instruction, and a run-time R_X86_64_RELATIVE relocation entry that
> > + * adds the 64-bit base address where the kernel is loaded.
> > + *
> > + * Replacing it with (X-startup_32)(%reg) results in the offset being stored,
> > + * and no run-time relocation.
> > + *
> > + * The macro should be used as a displacement with a base register containing
> > + * the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an immediate
> > + * [$ rva(X)].
> > + *
> > + * This macro can only be used from within the .head.text section, since the
> > + * expression requires startup_32 to be in the same section as the code being
> > + * assembled.
> > + */
> > +#define rva(X) ((X) - startup_32)
> > +
> > .code32
> > SYM_FUNC_START(startup_32)
> > /*
> >
> > Thanks.
> >
>
> With LLVM/Clang/LLD I see:
>
> mycompiler -Wp,-MD,arch/x86/boot/compressed/.kernel_info.o.d
> -nostdinc -isystem
> /home/dileks/src/llvm-toolchain/install/lib/clang/10.0.1rc1/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 -m64 -O2
> -fno-strict-aliasing -fPIE -DDISABLE_BRANCH_PROFILING -mcmodel=small
> -mno-mmx -mno-sse -ffreestanding -fno-stack-protector
> -Wno-address-of-packed-member -Wno-gnu -Wno-pointer-sign
> -fmacro-prefix-map=./= -fno-asynchronous-unwind-tables -include
> hidden.h -D__ASSEMBLY__ -c -o
> arch/x86/boot/compressed/kernel_info.o
> arch/x86/boot/compressed/kernel_info.S
> <built-in>:345:10: fatal error: 'hidden.h' file not found
> #include "hidden.h"
> ^~~~~~~~~~
> 1 error generated.
> make[5]: *** [scripts/Makefile.build:349:
> arch/x86/boot/compressed/kernel_info.o] Error 1
> make[4]: *** [arch/x86/boot/Makefile:114:
> arch/x86/boot/compressed/vmlinux] Error 2
> make[4]: *** Waiting for unfinished jobs....
>
> mycompiler is a wrapper-script to use ccache * clang-10 as compiler.
>
> patchset to previous build:
>
> $ git log --no-merges --oneline 5.7.0-rc7-1-amd64-clang..5.7.0-rc7-2-amd64-clang
> 8b74901cb9e5 (for-5.7/x86-boot-remove-runtime-relocations-from-compressed-kernel-v2-nivedita76)
> x86/boot: Check that there are no runtime relocations
> 83fb1bc3b076 x86/boot: Remove runtime relocations from head_{32,64}.S
> fede23dacbbd x86/boot: Remove run-time relocations from .head.text code
> 3e5ea481b8fb x86/boot: Add .text.* to setup.ld
> bec910ba3d67 x86/boot/compressed: Get rid of GOT fixup code
> be834cee6f39 x86/boot/compressed: Force hidden visibility for all
> symbol references
> 9b7c7d8d2d7b x86/boot/compressed: Move .got.plt entries out of the .got section
> ba6a49f806a0 (for-5.7/kbuild-compressed-debug-info) Makefile: support
> compressed debug info
> a1fb11944d11 (for-5.7/x86-boot-nivedita76) x86/boot: Correct
> relocation destination on old linkers
> c70e3890058f (for-5.7/x86-build-maskray) x86/boot: Discard
> .discard.unreachable for arch/x86/boot/compressed/vmlinux
>
> $ find ./ -name hidden.h
> ./drivers/firmware/efi/libstub/hidden.h
> ./arch/x86/boot/compressed/hidden.h
>
> Any thoughts?
>
Maybe this should be:
[ arch/x86/boot/compressed/Makefile ]
-KBUILD_CFLAGS += -include hidden.h
+KBUILD_CFLAGS += -include ./hidden.h
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 14:55 ` Sedat Dilek
@ 2020-05-26 15:07 ` Sedat Dilek
2020-05-26 15:31 ` Arvind Sankar
2020-05-26 16:18 ` Sedat Dilek
0 siblings, 2 replies; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 15:07 UTC (permalink / raw)
To: Ard Biesheuvel
Cc: Arvind Sankar, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 4:55 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Tue, May 26, 2020 at 4:48 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > On Tue, May 26, 2020 at 2:44 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > >
> > > On Tue, May 26, 2020 at 2:33 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > > >
> > > > On Tue, May 26, 2020 at 2:30 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> > > > >
> > > > > On Tue, 26 May 2020 at 14:29, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > > > > >
> > > > > > On Tue, May 26, 2020 at 12:59 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > > > > > >
> > > > > > > The compressed kernel currently contains bogus runtime relocations in
> > > > > > > the startup code in head_{32,64}.S, which are generated by the linker,
> > > > > > > but must not actually be processed at runtime.
> > > > > > >
> > > > > > > This generates warnings when linking with the BFD linker, and errors
> > > > > > > with LLD, which defaults to erroring on runtime 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 normally have
> > > > > > > R_X86_64_RELATIVE relocations.
> > > > > > >
> > > > > > > This series aims to get rid of these relocations. It is based on
> > > > > > > efi/next, where the latest patches touch the head code to eliminate the
> > > > > > > global offset table.
> > > > > > >
> > > > > > > The first patch is an independent fix for LLD, to avoid an orphan
> > > > > > > section in arch/x86/boot/setup.elf.
> > > > > > >
> > > > > > > The second 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 third patch addresses a remaining issue with the BFD linker, which
> > > > > > > insists on generating runtime 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
> > > > > > > runtime relocations get reintroduced. Since the GOT has been eliminated
> > > > > > > as well, the compressed kernel has no runtime relocations whatsoever any
> > > > > > > more.
> > > > > > >
> > > > > > > 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.
> > > > > > >
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > I would like to test this patchset v2 on top of Linux v5.7-rc7 together with:
> > > > > >
> > > > > > [1] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux
> > > > > > [2] x86/boot: Correct relocation destination on old linkers
> > > > > >
> > > > > > I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the
> > > > > > merge problems, but I am not sure I did it correctly.
> > > > > > So, which patches are really relevant from efi/next?
> > > > > >
> > > > > > What's your suggestions?
> > > > > >
> > > > >
> > > > > efi/next is here:
> > > > >
> > > > > https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/log/?h=next
> > > > >
> > > > > You'll need the top 3 patches.
> > > >
> > > > Thanks /o\.
> > > >
> > > > - Sedat -
> > >
> > > Are those diffs correct when using "x86/boot: Correct relocation
> > > destination on old linkers"?
> > >
> > > $ cat ../head_32_S.diff
> > > diff --cc arch/x86/boot/compressed/head_32.S
> > > index 064e895bad92,03557f2174bf..000000000000
> > > --- a/arch/x86/boot/compressed/head_32.S
> > > +++ b/arch/x86/boot/compressed/head_32.S
> > > @@@ -49,13 -49,17 +49,14 @@@
> > > * Position Independent Executable (PIE) so that linker won't optimize
> > > * R_386_GOT32X relocation to its fixed symbol address. Older
> > > * linkers generate R_386_32 relocations against locally defined symbols,
> > > - * _bss, _ebss, in PIE. It isn't wrong, just suboptimal compared
> > > - * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less
> > > - * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
> > > ++ * _bss, _ebss, _end in PIE. It isn't wrong, just suboptimal compared
> > > + * to R_386_RELATIVE. But the x86 kernel fails to properly handle
> > > * R_386_32 relocations when relocating the kernel. To generate
> > > - * R_386_RELATIVE relocations, we mark _bss and _ebss as hidden:
> > > - * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as
> > > - * hidden:
> > > ++ * R_386_RELATIVE relocations, we mark _bss, _ebss and _end as hidden:
> > > */
> > > .hidden _bss
> > > .hidden _ebss
> > > - .hidden _got
> > > - .hidden _egot
> > > + .hidden _end
> > >
> > > __HEAD
> > > SYM_FUNC_START(startup_32)
> > >
> > > $ cat ../head_64_S.diff
> > > diff --cc arch/x86/boot/compressed/head_64.S
> > > index 4b7ad1dfbea6,76d1d64d51e3..000000000000
> > > --- a/arch/x86/boot/compressed/head_64.S
> > > +++ b/arch/x86/boot/compressed/head_64.S
> > > @@@ -40,34 -40,11 +40,35 @@@
> > > */
> > > .hidden _bss
> > > .hidden _ebss
> > > - .hidden _got
> > > - .hidden _egot
> > > + .hidden _end
> > >
> > > __HEAD
> > > +
> > > +/*
> > > + * This macro gives the relative virtual address of X, i.e. the offset of X
> > > + * from startup_32. This is the same as the link-time virtual address of X,
> > > + * since startup_32 is at 0, but defining it this way tells the
> > > + * assembler/linker that we do not want the actual run-time address of X. This
> > > + * prevents the linker from trying to create unwanted run-time relocation
> > > + * entries for the reference when the compressed kernel is linked as PIE.
> > > + *
> > > + * A reference X(%reg) will result in the link-time VA of X being stored with
> > > + * the instruction, and a run-time R_X86_64_RELATIVE relocation entry that
> > > + * adds the 64-bit base address where the kernel is loaded.
> > > + *
> > > + * Replacing it with (X-startup_32)(%reg) results in the offset being stored,
> > > + * and no run-time relocation.
> > > + *
> > > + * The macro should be used as a displacement with a base register containing
> > > + * the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an immediate
> > > + * [$ rva(X)].
> > > + *
> > > + * This macro can only be used from within the .head.text section, since the
> > > + * expression requires startup_32 to be in the same section as the code being
> > > + * assembled.
> > > + */
> > > +#define rva(X) ((X) - startup_32)
> > > +
> > > .code32
> > > SYM_FUNC_START(startup_32)
> > > /*
> > >
> > > Thanks.
> > >
> >
> > With LLVM/Clang/LLD I see:
> >
> > mycompiler -Wp,-MD,arch/x86/boot/compressed/.kernel_info.o.d
> > -nostdinc -isystem
> > /home/dileks/src/llvm-toolchain/install/lib/clang/10.0.1rc1/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 -m64 -O2
> > -fno-strict-aliasing -fPIE -DDISABLE_BRANCH_PROFILING -mcmodel=small
> > -mno-mmx -mno-sse -ffreestanding -fno-stack-protector
> > -Wno-address-of-packed-member -Wno-gnu -Wno-pointer-sign
> > -fmacro-prefix-map=./= -fno-asynchronous-unwind-tables -include
> > hidden.h -D__ASSEMBLY__ -c -o
> > arch/x86/boot/compressed/kernel_info.o
> > arch/x86/boot/compressed/kernel_info.S
> > <built-in>:345:10: fatal error: 'hidden.h' file not found
> > #include "hidden.h"
> > ^~~~~~~~~~
> > 1 error generated.
> > make[5]: *** [scripts/Makefile.build:349:
> > arch/x86/boot/compressed/kernel_info.o] Error 1
> > make[4]: *** [arch/x86/boot/Makefile:114:
> > arch/x86/boot/compressed/vmlinux] Error 2
> > make[4]: *** Waiting for unfinished jobs....
> >
> > mycompiler is a wrapper-script to use ccache * clang-10 as compiler.
> >
> > patchset to previous build:
> >
> > $ git log --no-merges --oneline 5.7.0-rc7-1-amd64-clang..5.7.0-rc7-2-amd64-clang
> > 8b74901cb9e5 (for-5.7/x86-boot-remove-runtime-relocations-from-compressed-kernel-v2-nivedita76)
> > x86/boot: Check that there are no runtime relocations
> > 83fb1bc3b076 x86/boot: Remove runtime relocations from head_{32,64}.S
> > fede23dacbbd x86/boot: Remove run-time relocations from .head.text code
> > 3e5ea481b8fb x86/boot: Add .text.* to setup.ld
> > bec910ba3d67 x86/boot/compressed: Get rid of GOT fixup code
> > be834cee6f39 x86/boot/compressed: Force hidden visibility for all
> > symbol references
> > 9b7c7d8d2d7b x86/boot/compressed: Move .got.plt entries out of the .got section
> > ba6a49f806a0 (for-5.7/kbuild-compressed-debug-info) Makefile: support
> > compressed debug info
> > a1fb11944d11 (for-5.7/x86-boot-nivedita76) x86/boot: Correct
> > relocation destination on old linkers
> > c70e3890058f (for-5.7/x86-build-maskray) x86/boot: Discard
> > .discard.unreachable for arch/x86/boot/compressed/vmlinux
> >
> > $ find ./ -name hidden.h
> > ./drivers/firmware/efi/libstub/hidden.h
> > ./arch/x86/boot/compressed/hidden.h
> >
> > Any thoughts?
> >
>
> Maybe this should be:
>
> [ arch/x86/boot/compressed/Makefile ]
>
> -KBUILD_CFLAGS += -include hidden.h
> +KBUILD_CFLAGS += -include ./hidden.h
>
NOPE.
This works:
[ arch/x86/boot/compressed/Makefile ]
-KBUILD_CFLAGS += -include hidden.h
+KBUILD_CFLAGS += -include ./arch/x86/boot/compressed/hidden.h
$ ll arch/x86/boot/bzImage arch/x86/boot/compressed/vmlinux
-rw-r--r-- 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/bzImage
-rwxr-xr-x 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/compressed/vmlinux
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 15:07 ` Sedat Dilek
@ 2020-05-26 15:31 ` Arvind Sankar
2020-05-27 6:24 ` Sedat Dilek
2020-05-26 16:18 ` Sedat Dilek
1 sibling, 1 reply; 53+ messages in thread
From: Arvind Sankar @ 2020-05-26 15:31 UTC (permalink / raw)
To: Sedat Dilek
Cc: Ard Biesheuvel, Arvind Sankar, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, H. Peter Anvin, X86 ML, Nick Desaulniers,
Fangrui Song, Dmitry Golovin, Clang-Built-Linux ML,
Masahiro Yamada, Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 05:07:24PM +0200, Sedat Dilek wrote:
> > >
> >
> > Maybe this should be:
> >
> > [ arch/x86/boot/compressed/Makefile ]
> >
> > -KBUILD_CFLAGS += -include hidden.h
> > +KBUILD_CFLAGS += -include ./hidden.h
> >
>
> NOPE.
>
> This works:
>
> [ arch/x86/boot/compressed/Makefile ]
>
> -KBUILD_CFLAGS += -include hidden.h
> +KBUILD_CFLAGS += -include ./arch/x86/boot/compressed/hidden.h
>
> $ ll arch/x86/boot/bzImage arch/x86/boot/compressed/vmlinux
> -rw-r--r-- 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/bzImage
> -rwxr-xr-x 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/compressed/vmlinux
>
> - Sedat -
It needs to either be $(srctree)/$(src)/hidden.h, or we should add
-I $(srctree)/$(src) to the KBUILD_CFLAGS. The latter option is added
automatically when building in a separate builddir with O=${KOBJ} (which
is how I, and I assume Ard, was testing), but for some reason is not
added when building in-tree. The -include option doesn't automatically
search the directory of the source file.
-include file Process file as if "#include "file"" appeared as the first
line of the primary source file. However, the first directory searched
for file is the preprocessor's working directory instead of the
directory containing the main source file. If not found there, it is
searched for in the remainder of the "#include "..."" search chain as
normal.
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 15:31 ` Arvind Sankar
@ 2020-05-27 6:24 ` Sedat Dilek
0 siblings, 0 replies; 53+ messages in thread
From: Sedat Dilek @ 2020-05-27 6:24 UTC (permalink / raw)
To: Arvind Sankar
Cc: Ard Biesheuvel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 5:31 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> On Tue, May 26, 2020 at 05:07:24PM +0200, Sedat Dilek wrote:
> > > >
> > >
> > > Maybe this should be:
> > >
> > > [ arch/x86/boot/compressed/Makefile ]
> > >
> > > -KBUILD_CFLAGS += -include hidden.h
> > > +KBUILD_CFLAGS += -include ./hidden.h
> > >
> >
> > NOPE.
> >
> > This works:
> >
> > [ arch/x86/boot/compressed/Makefile ]
> >
> > -KBUILD_CFLAGS += -include hidden.h
> > +KBUILD_CFLAGS += -include ./arch/x86/boot/compressed/hidden.h
> >
> > $ ll arch/x86/boot/bzImage arch/x86/boot/compressed/vmlinux
> > -rw-r--r-- 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/bzImage
> > -rwxr-xr-x 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/compressed/vmlinux
> >
> > - Sedat -
>
> It needs to either be $(srctree)/$(src)/hidden.h, or we should add
> -I $(srctree)/$(src) to the KBUILD_CFLAGS. The latter option is added
> automatically when building in a separate builddir with O=${KOBJ} (which
> is how I, and I assume Ard, was testing), but for some reason is not
> added when building in-tree. The -include option doesn't automatically
> search the directory of the source file.
>
> -include file Process file as if "#include "file"" appeared as the first
> line of the primary source file. However, the first directory searched
> for file is the preprocessor's working directory instead of the
> directory containing the main source file. If not found there, it is
> searched for in the remainder of the "#include "..."" search chain as
> normal.
Will you send a follow-up or a v3 for this?
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-26 15:07 ` Sedat Dilek
2020-05-26 15:31 ` Arvind Sankar
@ 2020-05-26 16:18 ` Sedat Dilek
1 sibling, 0 replies; 53+ messages in thread
From: Sedat Dilek @ 2020-05-26 16:18 UTC (permalink / raw)
To: Ard Biesheuvel
Cc: Arvind Sankar, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, Clang-Built-Linux ML, Masahiro Yamada,
Daniel Kiper, Linux Kernel Mailing List
On Tue, May 26, 2020 at 5:07 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
...
> > > patchset to previous build:
> > >
> > > $ git log --no-merges --oneline 5.7.0-rc7-1-amd64-clang..5.7.0-rc7-2-amd64-clang
> > > 8b74901cb9e5 (for-5.7/x86-boot-remove-runtime-relocations-from-compressed-kernel-v2-nivedita76)
> > > x86/boot: Check that there are no runtime relocations
> > > 83fb1bc3b076 x86/boot: Remove runtime relocations from head_{32,64}.S
> > > fede23dacbbd x86/boot: Remove run-time relocations from .head.text code
> > > 3e5ea481b8fb x86/boot: Add .text.* to setup.ld
> > > bec910ba3d67 x86/boot/compressed: Get rid of GOT fixup code
> > > be834cee6f39 x86/boot/compressed: Force hidden visibility for all
> > > symbol references
> > > 9b7c7d8d2d7b x86/boot/compressed: Move .got.plt entries out of the .got section
> > > ba6a49f806a0 (for-5.7/kbuild-compressed-debug-info) Makefile: support
> > > compressed debug info
> > > a1fb11944d11 (for-5.7/x86-boot-nivedita76) x86/boot: Correct
> > > relocation destination on old linkers
> > > c70e3890058f (for-5.7/x86-build-maskray) x86/boot: Discard
> > > .discard.unreachable for arch/x86/boot/compressed/vmlinux
...
> This works:
>
> [ arch/x86/boot/compressed/Makefile ]
>
> -KBUILD_CFLAGS += -include hidden.h
> +KBUILD_CFLAGS += -include ./arch/x86/boot/compressed/hidden.h
>
> $ ll arch/x86/boot/bzImage arch/x86/boot/compressed/vmlinux
> -rw-r--r-- 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/bzImage
> -rwxr-xr-x 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/compressed/vmlinux
>
I was able to build/link and boot on bare metal.
root@iniza:~# cat /proc/version
Linux version 5.7.0-rc7-2-amd64-clang (sedat.dilek@gmail.com@iniza)
(clang version 10.0.1rc1, LLD 10.0.1rc1) #2~bullseye+dileks1 SMP
2020-05-26
- Sedat -
^ permalink raw reply [flat|nested] 53+ messages in thread
* [PATCH v2 1/4] x86/boot: Add .text.* to setup.ld
2020-05-24 21:28 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
2020-05-25 7:10 ` Ard Biesheuvel
2020-05-25 22:59 ` [PATCH v2 " Arvind Sankar
@ 2020-05-25 22:59 ` Arvind Sankar
2020-05-25 22:59 ` [PATCH v2 2/4] x86/boot: Remove run-time relocations from .head.text code Arvind Sankar
` (3 subsequent siblings)
6 siblings, 0 replies; 53+ messages in thread
From: Arvind Sankar @ 2020-05-25 22:59 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, Borislav Petkov, H. Peter Anvin, x86
Cc: Nick Desaulniers, Fangrui Song, Dmitry Golovin,
clang-built-linux, Ard Biesheuvel, Masahiro Yamada, Daniel Kiper,
linux-kernel
gcc puts the main function into .text.startup when compiled with -Os (or
-O2). This results in arch/x86/boot/main.c having a .text.startup
section which is currently not included explicitly in the linker script
setup.ld in the same directory.
The BFD linker places this orphan section immediately after .text, so
this still works. However, LLD git, since [1], is choosing to place it
immediately after the .bstext section instead (this is the first code
section). This plays havoc with the section layout that setup.elf
requires to create the setup header, for eg on 64-bit:
LD arch/x86/boot/setup.elf
ld.lld: error: section .text.startup file range overlaps with .header
>>> .text.startup range is [0x200040, 0x2001FE]
>>> .header range is [0x2001EF, 0x20026B]
ld.lld: error: section .header file range overlaps with .bsdata
>>> .header range is [0x2001EF, 0x20026B]
>>> .bsdata range is [0x2001FF, 0x200398]
ld.lld: error: section .bsdata file range overlaps with .entrytext
>>> .bsdata range is [0x2001FF, 0x200398]
>>> .entrytext range is [0x20026C, 0x2002D3]
ld.lld: error: section .text.startup virtual address range overlaps
with .header
>>> .text.startup range is [0x40, 0x1FE]
>>> .header range is [0x1EF, 0x26B]
ld.lld: error: section .header virtual address range overlaps with
.bsdata
>>> .header range is [0x1EF, 0x26B]
>>> .bsdata range is [0x1FF, 0x398]
ld.lld: error: section .bsdata virtual address range overlaps with
.entrytext
>>> .bsdata range is [0x1FF, 0x398]
>>> .entrytext range is [0x26C, 0x2D3]
ld.lld: error: section .text.startup load address range overlaps with
.header
>>> .text.startup range is [0x40, 0x1FE]
>>> .header range is [0x1EF, 0x26B]
ld.lld: error: section .header load address range overlaps with
.bsdata
>>> .header range is [0x1EF, 0x26B]
>>> .bsdata range is [0x1FF, 0x398]
ld.lld: error: section .bsdata load address range overlaps with
.entrytext
>>> .bsdata range is [0x1FF, 0x398]
>>> .entrytext range is [0x26C, 0x2D3]
Add .text.* to the .text output section to fix this, and also prevent
any future surprises if the compiler decides to create other such
sections.
[1] https://reviews.llvm.org/D75225
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
arch/x86/boot/setup.ld | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld
index 24c95522f231..49546c247ae2 100644
--- a/arch/x86/boot/setup.ld
+++ b/arch/x86/boot/setup.ld
@@ -20,7 +20,7 @@ SECTIONS
.initdata : { *(.initdata) }
__end_init = .;
- .text : { *(.text) }
+ .text : { *(.text .text.*) }
.text32 : { *(.text32) }
. = ALIGN(16);
--
2.26.2
^ permalink raw reply related [flat|nested] 53+ messages in thread* [PATCH v2 2/4] x86/boot: Remove run-time relocations from .head.text code
2020-05-24 21:28 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
` (2 preceding siblings ...)
2020-05-25 22:59 ` [PATCH v2 1/4] x86/boot: Add .text.* to setup.ld Arvind Sankar
@ 2020-05-25 22:59 ` Arvind Sankar
2020-05-25 22:59 ` [PATCH v2 3/4] x86/boot: Remove runtime relocations from head_{32,64}.S Arvind Sankar
` (2 subsequent siblings)
6 siblings, 0 replies; 53+ messages in thread
From: Arvind Sankar @ 2020-05-25 22:59 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, Borislav Petkov, H. Peter Anvin, x86
Cc: Nick Desaulniers, Fangrui Song, Dmitry Golovin,
clang-built-linux, Ard Biesheuvel, Masahiro Yamada, Daniel Kiper,
linux-kernel
The assembly code in head_{32,64}.S, while meant to be
position-independent, generates run-time relocations because it uses
instructions such as
leal gdt(%edx), %eax
which make the assembler and linker think that the code is using %edx as
an index into gdt, and hence gdt needs to be relocated to its run-time
address.
On 32-bit, with lld Dmitry Golovin reports that this results in a
link-time error with default options (i.e. unless -z notext is
explicitly passed):
LD arch/x86/boot/compressed/vmlinux
ld.lld: error: can't create dynamic relocation R_386_32 against local
symbol in readonly segment; recompile object files with -fPIC or pass
'-Wl,-z,notext' to allow text relocations in the output
With the BFD linker, this generates a warning during the build, if
--warn-shared-textrel is enabled, which at least Gentoo enables by
default:
LD arch/x86/boot/compressed/vmlinux
ld: arch/x86/boot/compressed/head_32.o: warning: relocation in read-only section `.head.text'
ld: warning: creating a DT_TEXTREL in object
On 64-bit, it is not possible to link the kernel as -pie with lld, and
it is only possible with a BFD linker that supports -z noreloc-overflow,
i.e. versions >2.26. This is because these instructions cannot really be
relocated: the displacement field is only 32-bits wide, and thus cannot
be relocated for a 64-bit load address. The -z noreloc-overflow option
simply overrides the linker error, and results in R_X86_64_RELATIVE
relocations that apply a 64-bit relocation to a 32-bit field anyway.
This happens to work because nothing will process these run-time
relocations.
Start fixing this by removing relocations from .head.text:
- On 32-bit, use a base register that holds the address of the GOT and
reference symbol addresses using @GOTOFF, i.e.
leal gdt@GOTOFF(%edx), %eax
- On 64-bit, most of the code can (and already does) use %rip-relative
addressing, however the .code32 bits can't, and the 64-bit code also
needs to reference symbol addresses as they will be after moving the
compressed kernel to the end of the decompression buffer.
For these cases, reference the symbols as an offset to startup_32 to
avoid creating relocations, i.e.
leal (gdt-startup_32)(%bp), %eax
This only works in .head.text as the subtraction cannot be represented
as a PC-relative relocation unless startup_32 is in the same section
as the code. Move efi32_pe_entry into .head.text so that it can use
the same method to avoid relocations.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
arch/x86/boot/compressed/head_32.S | 40 +++++------
arch/x86/boot/compressed/head_64.S | 104 ++++++++++++++++++-----------
2 files changed, 86 insertions(+), 58 deletions(-)
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index dfa4131c65df..66657bb99aae 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -73,10 +73,10 @@ SYM_FUNC_START(startup_32)
leal (BP_scratch+4)(%esi), %esp
call 1f
1: popl %edx
- subl $1b, %edx
+ addl $_GLOBAL_OFFSET_TABLE_+(.-1b), %edx
/* Load new GDT */
- leal gdt(%edx), %eax
+ leal gdt@GOTOFF(%edx), %eax
movl %eax, 2(%eax)
lgdt (%eax)
@@ -89,14 +89,16 @@ SYM_FUNC_START(startup_32)
movl %eax, %ss
/*
- * %edx contains the address we are loaded at by the boot loader and %ebx
- * contains the address where we should move the kernel image temporarily
- * for safe in-place decompression. %ebp contains the address that the kernel
- * will be decompressed to.
+ * %edx contains the address we are loaded at by the boot loader (plus the
+ * offset to the GOT). The below code calculates %ebx to be the address where
+ * we should move the kernel image temporarily for safe in-place decompression
+ * (again, plus the offset to the GOT).
+ *
+ * %ebp is calculated to be the address that the kernel will be decompressed to.
*/
#ifdef CONFIG_RELOCATABLE
- movl %edx, %ebx
+ leal startup_32@GOTOFF(%edx), %ebx
#ifdef CONFIG_EFI_STUB
/*
@@ -107,7 +109,7 @@ SYM_FUNC_START(startup_32)
* image_offset = startup_32 - image_base
* Otherwise image_offset will be zero and has no effect on the calculations.
*/
- subl image_offset(%edx), %ebx
+ subl image_offset@GOTOFF(%edx), %ebx
#endif
movl BP_kernel_alignment(%esi), %eax
@@ -124,10 +126,10 @@ SYM_FUNC_START(startup_32)
movl %ebx, %ebp // Save the output address for later
/* Target address to relocate to for decompression */
addl BP_init_size(%esi), %ebx
- subl $_end, %ebx
+ subl $_end@GOTOFF, %ebx
/* Set up the stack */
- leal boot_stack_end(%ebx), %esp
+ leal boot_stack_end@GOTOFF(%ebx), %esp
/* Zero EFLAGS */
pushl $0
@@ -138,8 +140,8 @@ SYM_FUNC_START(startup_32)
* where decompression in place becomes safe.
*/
pushl %esi
- leal (_bss-4)(%edx), %esi
- leal (_bss-4)(%ebx), %edi
+ leal (_bss@GOTOFF-4)(%edx), %esi
+ leal (_bss@GOTOFF-4)(%ebx), %edi
movl $(_bss - startup_32), %ecx
shrl $2, %ecx
std
@@ -152,14 +154,14 @@ SYM_FUNC_START(startup_32)
* during extract_kernel below. To avoid any issues, repoint the GDTR
* to the new copy of the GDT.
*/
- leal gdt(%ebx), %eax
+ leal gdt@GOTOFF(%ebx), %eax
movl %eax, 2(%eax)
lgdt (%eax)
/*
* Jump to the relocated address.
*/
- leal .Lrelocated(%ebx), %eax
+ leal .Lrelocated@GOTOFF(%ebx), %eax
jmp *%eax
SYM_FUNC_END(startup_32)
@@ -169,7 +171,7 @@ SYM_FUNC_START_ALIAS(efi_stub_entry)
add $0x4, %esp
movl 8(%esp), %esi /* save boot_params pointer */
call efi_main
- leal startup_32(%eax), %eax
+ /* efi_main returns the possibly relocated address of startup_32 */
jmp *%eax
SYM_FUNC_END(efi32_stub_entry)
SYM_FUNC_END_ALIAS(efi_stub_entry)
@@ -182,8 +184,8 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
* Clear BSS (stack is currently empty)
*/
xorl %eax, %eax
- leal _bss(%ebx), %edi
- leal _ebss(%ebx), %ecx
+ leal _bss@GOTOFF(%ebx), %edi
+ leal _ebss@GOTOFF(%ebx), %ecx
subl %edi, %ecx
shrl $2, %ecx
rep stosl
@@ -197,9 +199,9 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
pushl %ebp /* output address */
pushl $z_input_len /* input_len */
- leal input_data(%ebx), %eax
+ leal input_data@GOTOFF(%ebx), %eax
pushl %eax /* input_data */
- leal boot_heap(%ebx), %eax
+ leal boot_heap@GOTOFF(%ebx), %eax
pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call extract_kernel /* returns kernel location in %eax */
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 706fbf6eef53..18b0edcb23d2 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -42,6 +42,32 @@
.hidden _ebss
__HEAD
+
+/*
+ * This macro gives the relative virtual address of X, i.e. the offset of X
+ * from startup_32. This is the same as the link-time virtual address of X,
+ * since startup_32 is at 0, but defining it this way tells the
+ * assembler/linker that we do not want the actual run-time address of X. This
+ * prevents the linker from trying to create unwanted run-time relocation
+ * entries for the reference when the compressed kernel is linked as PIE.
+ *
+ * A reference X(%reg) will result in the link-time VA of X being stored with
+ * the instruction, and a run-time R_X86_64_RELATIVE relocation entry that
+ * adds the 64-bit base address where the kernel is loaded.
+ *
+ * Replacing it with (X-startup_32)(%reg) results in the offset being stored,
+ * and no run-time relocation.
+ *
+ * The macro should be used as a displacement with a base register containing
+ * the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an immediate
+ * [$ rva(X)].
+ *
+ * This macro can only be used from within the .head.text section, since the
+ * expression requires startup_32 to be in the same section as the code being
+ * assembled.
+ */
+#define rva(X) ((X) - startup_32)
+
.code32
SYM_FUNC_START(startup_32)
/*
@@ -64,10 +90,10 @@ SYM_FUNC_START(startup_32)
leal (BP_scratch+4)(%esi), %esp
call 1f
1: popl %ebp
- subl $1b, %ebp
+ subl $ rva(1b), %ebp
/* Load new GDT with the 64bit segments using 32bit descriptor */
- leal gdt(%ebp), %eax
+ leal rva(gdt)(%ebp), %eax
movl %eax, 2(%eax)
lgdt (%eax)
@@ -80,7 +106,7 @@ SYM_FUNC_START(startup_32)
movl %eax, %ss
/* setup a stack and make sure cpu supports long mode. */
- leal boot_stack_end(%ebp), %esp
+ leal rva(boot_stack_end)(%ebp), %esp
call verify_cpu
testl %eax, %eax
@@ -107,7 +133,7 @@ SYM_FUNC_START(startup_32)
* image_offset = startup_32 - image_base
* Otherwise image_offset will be zero and has no effect on the calculations.
*/
- subl image_offset(%ebp), %ebx
+ subl rva(image_offset)(%ebp), %ebx
#endif
movl BP_kernel_alignment(%esi), %eax
@@ -123,7 +149,7 @@ SYM_FUNC_START(startup_32)
/* Target address to relocate to for decompression */
addl BP_init_size(%esi), %ebx
- subl $_end, %ebx
+ subl $ rva(_end), %ebx
/*
* Prepare for entering 64 bit mode
@@ -151,19 +177,19 @@ SYM_FUNC_START(startup_32)
1:
/* Initialize Page tables to 0 */
- leal pgtable(%ebx), %edi
+ leal rva(pgtable)(%ebx), %edi
xorl %eax, %eax
movl $(BOOT_INIT_PGT_SIZE/4), %ecx
rep stosl
/* Build Level 4 */
- leal pgtable + 0(%ebx), %edi
+ leal rva(pgtable + 0)(%ebx), %edi
leal 0x1007 (%edi), %eax
movl %eax, 0(%edi)
addl %edx, 4(%edi)
/* Build Level 3 */
- leal pgtable + 0x1000(%ebx), %edi
+ leal rva(pgtable + 0x1000)(%ebx), %edi
leal 0x1007(%edi), %eax
movl $4, %ecx
1: movl %eax, 0x00(%edi)
@@ -174,7 +200,7 @@ SYM_FUNC_START(startup_32)
jnz 1b
/* Build Level 2 */
- leal pgtable + 0x2000(%ebx), %edi
+ leal rva(pgtable + 0x2000)(%ebx), %edi
movl $0x00000183, %eax
movl $2048, %ecx
1: movl %eax, 0(%edi)
@@ -185,7 +211,7 @@ SYM_FUNC_START(startup_32)
jnz 1b
/* Enable the boot page tables */
- leal pgtable(%ebx), %eax
+ leal rva(pgtable)(%ebx), %eax
movl %eax, %cr3
/* Enable Long mode in EFER (Extended Feature Enable Register) */
@@ -211,17 +237,17 @@ SYM_FUNC_START(startup_32)
* used to perform that far jump.
*/
pushl $__KERNEL_CS
- leal startup_64(%ebp), %eax
+ leal rva(startup_64)(%ebp), %eax
#ifdef CONFIG_EFI_MIXED
- movl efi32_boot_args(%ebp), %edi
+ movl rva(efi32_boot_args)(%ebp), %edi
cmp $0, %edi
jz 1f
- leal efi64_stub_entry(%ebp), %eax
- movl efi32_boot_args+4(%ebp), %esi
- movl efi32_boot_args+8(%ebp), %edx // saved bootparams pointer
+ leal rva(efi64_stub_entry)(%ebp), %eax
+ movl rva(efi32_boot_args+4)(%ebp), %esi
+ movl rva(efi32_boot_args+8)(%ebp), %edx // saved bootparams pointer
cmpl $0, %edx
jnz 1f
- leal efi_pe_entry(%ebp), %eax
+ leal rva(efi_pe_entry)(%ebp), %eax
movl %edi, %ecx // MS calling convention
movl %esi, %edx
1:
@@ -246,18 +272,18 @@ SYM_FUNC_START(efi32_stub_entry)
call 1f
1: pop %ebp
- subl $1b, %ebp
+ subl $ rva(1b), %ebp
- movl %esi, efi32_boot_args+8(%ebp)
+ movl %esi, rva(efi32_boot_args+8)(%ebp)
SYM_INNER_LABEL(efi32_pe_stub_entry, SYM_L_LOCAL)
- movl %ecx, efi32_boot_args(%ebp)
- movl %edx, efi32_boot_args+4(%ebp)
- movb $0, efi_is64(%ebp)
+ movl %ecx, rva(efi32_boot_args)(%ebp)
+ movl %edx, rva(efi32_boot_args+4)(%ebp)
+ movb $0, rva(efi_is64)(%ebp)
/* Save firmware GDTR and code/data selectors */
- sgdtl efi32_boot_gdt(%ebp)
- movw %cs, efi32_boot_cs(%ebp)
- movw %ds, efi32_boot_ds(%ebp)
+ sgdtl rva(efi32_boot_gdt)(%ebp)
+ movw %cs, rva(efi32_boot_cs)(%ebp)
+ movw %ds, rva(efi32_boot_ds)(%ebp)
/* Disable paging */
movl %cr0, %eax
@@ -336,11 +362,11 @@ SYM_CODE_START(startup_64)
/* Target address to relocate to for decompression */
movl BP_init_size(%rsi), %ebx
- subl $_end, %ebx
+ subl $ rva(_end), %ebx
addq %rbp, %rbx
/* Set up the stack */
- leaq boot_stack_end(%rbx), %rsp
+ leaq rva(boot_stack_end)(%rbx), %rsp
/*
* At this point we are in long mode with 4-level paging enabled,
@@ -406,7 +432,7 @@ SYM_CODE_START(startup_64)
lretq
trampoline_return:
/* Restore the stack, the 32-bit trampoline uses its own stack */
- leaq boot_stack_end(%rbx), %rsp
+ leaq rva(boot_stack_end)(%rbx), %rsp
/*
* cleanup_trampoline() would restore trampoline memory.
@@ -418,7 +444,7 @@ trampoline_return:
* this function call.
*/
pushq %rsi
- leaq top_pgtable(%rbx), %rdi
+ leaq rva(top_pgtable)(%rbx), %rdi
call cleanup_trampoline
popq %rsi
@@ -432,9 +458,9 @@ trampoline_return:
*/
pushq %rsi
leaq (_bss-8)(%rip), %rsi
- leaq (_bss-8)(%rbx), %rdi
- movq $_bss /* - $startup_32 */, %rcx
- shrq $3, %rcx
+ leaq rva(_bss-8)(%rbx), %rdi
+ movl $(_bss - startup_32), %ecx
+ shrl $3, %ecx
std
rep movsq
cld
@@ -445,15 +471,15 @@ trampoline_return:
* during extract_kernel below. To avoid any issues, repoint the GDTR
* to the new copy of the GDT.
*/
- leaq gdt64(%rbx), %rax
- leaq gdt(%rbx), %rdx
+ leaq rva(gdt64)(%rbx), %rax
+ leaq rva(gdt)(%rbx), %rdx
movq %rdx, 2(%rax)
lgdt (%rax)
/*
* Jump to the relocated address.
*/
- leaq .Lrelocated(%rbx), %rax
+ leaq rva(.Lrelocated)(%rbx), %rax
jmp *%rax
SYM_CODE_END(startup_64)
@@ -465,7 +491,7 @@ SYM_FUNC_START_ALIAS(efi_stub_entry)
movq %rdx, %rbx /* save boot_params pointer */
call efi_main
movq %rbx,%rsi
- leaq startup_64(%rax), %rax
+ leaq rva(startup_64)(%rax), %rax
jmp *%rax
SYM_FUNC_END(efi64_stub_entry)
SYM_FUNC_END_ALIAS(efi_stub_entry)
@@ -628,7 +654,7 @@ SYM_DATA(efi_is64, .byte 1)
#define BS32_handle_protocol 88 // offsetof(efi_boot_services_32_t, handle_protocol)
#define LI32_image_base 32 // offsetof(efi_loaded_image_32_t, image_base)
- .text
+ __HEAD
.code32
SYM_FUNC_START(efi32_pe_entry)
/*
@@ -650,12 +676,12 @@ SYM_FUNC_START(efi32_pe_entry)
call 1f
1: pop %ebx
- subl $1b, %ebx
+ subl $ rva(1b), %ebx
/* Get the loaded image protocol pointer from the image handle */
leal -4(%ebp), %eax
pushl %eax // &loaded_image
- leal loaded_image_proto(%ebx), %eax
+ leal rva(loaded_image_proto)(%ebx), %eax
pushl %eax // pass the GUID address
pushl 8(%ebp) // pass the image handle
@@ -690,7 +716,7 @@ SYM_FUNC_START(efi32_pe_entry)
* use it before we get to the 64-bit efi_pe_entry() in C code.
*/
subl %esi, %ebx
- movl %ebx, image_offset(%ebp) // save image_offset
+ movl %ebx, rva(image_offset)(%ebp) // save image_offset
jmp efi32_pe_stub_entry
2: popl %edi // restore callee-save registers
--
2.26.2
^ permalink raw reply related [flat|nested] 53+ messages in thread* [PATCH v2 3/4] x86/boot: Remove runtime relocations from head_{32,64}.S
2020-05-24 21:28 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
` (3 preceding siblings ...)
2020-05-25 22:59 ` [PATCH v2 2/4] x86/boot: Remove run-time relocations from .head.text code Arvind Sankar
@ 2020-05-25 22:59 ` Arvind Sankar
2020-05-25 22:59 ` [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations Arvind Sankar
2020-05-26 0:37 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Fangrui Song
6 siblings, 0 replies; 53+ messages in thread
From: Arvind Sankar @ 2020-05-25 22:59 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, Borislav Petkov, H. Peter Anvin, x86
Cc: Nick Desaulniers, Fangrui Song, Dmitry Golovin,
clang-built-linux, Ard Biesheuvel, Masahiro Yamada, Daniel Kiper,
linux-kernel
The BFD linker generates runtime relocations for z_input_len and
z_output_len, even though they are absolute symbols.
This is fixed for binutils-2.35 [1]. Work around this for earlier
versions by defining two variables input_len and output_len in addition
to the symbols, and use them via position-independent references.
This eliminates the last two runtime relocations in the head code and
allows us to drop the -z noreloc-overflow flag to the linker.
[1] https://sourceware.org/bugzilla/show_bug.cgi?id=25754
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
arch/x86/boot/compressed/Makefile | 8 --------
arch/x86/boot/compressed/head_32.S | 17 ++++++++---------
arch/x86/boot/compressed/head_64.S | 4 ++--
arch/x86/boot/compressed/mkpiggy.c | 6 ++++++
4 files changed, 16 insertions(+), 19 deletions(-)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index aa9ed814e5fa..d3e882e855ee 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -49,15 +49,7 @@ UBSAN_SANITIZE :=n
KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
# Compressed kernel should be built as PIE since it may be loaded at any
# address by the bootloader.
-ifeq ($(CONFIG_X86_32),y)
KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
-else
-# To build 64-bit compressed kernel as PIE, we disable relocation
-# overflow check to avoid relocation overflow error with a new linker
-# command-line option, -z noreloc-overflow.
-KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \
- && echo "-z noreloc-overflow -pie --no-dynamic-linker")
-endif
LDFLAGS_vmlinux := -T
hostprogs := mkpiggy
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 66657bb99aae..064e895bad92 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -193,18 +193,17 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
/*
* Do the extraction, and jump to the new kernel..
*/
- /* push arguments for extract_kernel: */
- pushl $z_output_len /* decompressed length, end of relocs */
+ /* push arguments for extract_kernel: */
- pushl %ebp /* output address */
-
- pushl $z_input_len /* input_len */
+ pushl output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */
+ pushl %ebp /* output address */
+ pushl input_len@GOTOFF(%ebx) /* input_len */
leal input_data@GOTOFF(%ebx), %eax
- pushl %eax /* input_data */
+ pushl %eax /* input_data */
leal boot_heap@GOTOFF(%ebx), %eax
- pushl %eax /* heap area */
- pushl %esi /* real mode pointer */
- call extract_kernel /* returns kernel location in %eax */
+ pushl %eax /* heap area */
+ pushl %esi /* real mode pointer */
+ call extract_kernel /* returns kernel location in %eax */
addl $24, %esp
/*
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 18b0edcb23d2..4b7ad1dfbea6 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -517,9 +517,9 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
movq %rsi, %rdi /* real mode address */
leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
leaq input_data(%rip), %rdx /* input_data */
- movl $z_input_len, %ecx /* input_len */
+ movl input_len(%rip), %ecx /* input_len */
movq %rbp, %r8 /* output target address */
- movl $z_output_len, %r9d /* decompressed length, end of relocs */
+ movl output_len(%rip), %r9d /* decompressed length, end of relocs */
call extract_kernel /* returns kernel location in %rax */
popq %rsi
diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c
index 7e01248765b2..52aa56cdbacc 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -60,6 +60,12 @@ int main(int argc, char *argv[])
printf(".incbin \"%s\"\n", argv[1]);
printf("input_data_end:\n");
+ printf(".section \".rodata\",\"a\",@progbits\n");
+ printf(".globl input_len\n");
+ printf("input_len:\n\t.long %lu\n", ilen);
+ printf(".globl output_len\n");
+ printf("output_len:\n\t.long %lu\n", (unsigned long)olen);
+
retval = 0;
bail:
if (f)
--
2.26.2
^ permalink raw reply related [flat|nested] 53+ messages in thread* [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations
2020-05-24 21:28 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
` (4 preceding siblings ...)
2020-05-25 22:59 ` [PATCH v2 3/4] x86/boot: Remove runtime relocations from head_{32,64}.S Arvind Sankar
@ 2020-05-25 22:59 ` Arvind Sankar
2020-05-26 6:11 ` Ard Biesheuvel
2020-05-26 0:37 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Fangrui Song
6 siblings, 1 reply; 53+ messages in thread
From: Arvind Sankar @ 2020-05-25 22:59 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, Borislav Petkov, H. Peter Anvin, x86
Cc: Nick Desaulniers, Fangrui Song, Dmitry Golovin,
clang-built-linux, Ard Biesheuvel, Masahiro Yamada, Daniel Kiper,
linux-kernel
Add a linker script check that there are no runtime relocations, and
remove the old one that tries to check via looking for specially-named
sections in the object files.
Drop the tests for -fPIE compiler option and -pie linker option, as they
are available in all supported gcc and binutils versions (as well as
clang and lld).
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
arch/x86/boot/compressed/Makefile | 28 +++-----------------------
arch/x86/boot/compressed/vmlinux.lds.S | 8 ++++++++
2 files changed, 11 insertions(+), 25 deletions(-)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index d3e882e855ee..679a2b383bfe 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -27,7 +27,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4
KBUILD_CFLAGS := -m$(BITS) -O2
-KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC)
+KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
cflags-$(CONFIG_X86_32) := -march=i386
cflags-$(CONFIG_X86_64) := -mcmodel=small
@@ -49,7 +49,7 @@ UBSAN_SANITIZE :=n
KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
# Compressed kernel should be built as PIE since it may be loaded at any
# address by the bootloader.
-KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
+KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
LDFLAGS_vmlinux := -T
hostprogs := mkpiggy
@@ -84,30 +84,8 @@ vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
vmlinux-objs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
-# The compressed kernel is built with -fPIC/-fPIE so that a boot loader
-# can place it anywhere in memory and it will still run. However, since
-# it is executed as-is without any ELF relocation processing performed
-# (and has already had all relocation sections stripped from the binary),
-# none of the code can use data relocations (e.g. static assignments of
-# pointer values), since they will be meaningless at runtime. This check
-# will refuse to link the vmlinux if any of these relocations are found.
-quiet_cmd_check_data_rel = DATAREL $@
-define cmd_check_data_rel
- for obj in $(filter %.o,$^); do \
- $(READELF) -S $$obj | grep -qF .rel.local && { \
- echo "error: $$obj has data relocations!" >&2; \
- exit 1; \
- } || true; \
- done
-endef
-
-# We need to run two commands under "if_changed", so merge them into a
-# single invocation.
-quiet_cmd_check-and-link-vmlinux = LD $@
- cmd_check-and-link-vmlinux = $(cmd_check_data_rel); $(cmd_ld)
-
$(obj)/vmlinux: $(vmlinux-objs-y) FORCE
- $(call if_changed,check-and-link-vmlinux)
+ $(call if_changed,ld)
OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
$(obj)/vmlinux.bin: vmlinux FORCE
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index d826ab38a8f9..f9902c6ffe29 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -42,6 +42,12 @@ SECTIONS
*(.rodata.*)
_erodata = . ;
}
+ .rel.dyn : {
+ *(.rel.*)
+ }
+ .rela.dyn : {
+ *(.rela.*)
+ }
.got : {
*(.got)
}
@@ -83,3 +89,5 @@ ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT en
#else
ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!")
#endif
+
+ASSERT(SIZEOF(.rel.dyn) == 0 && SIZEOF(.rela.dyn) == 0, "Unexpected runtime relocations detected!")
--
2.26.2
^ permalink raw reply related [flat|nested] 53+ messages in thread* Re: [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations
2020-05-25 22:59 ` [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations Arvind Sankar
@ 2020-05-26 6:11 ` Ard Biesheuvel
2020-05-26 15:16 ` Arvind Sankar
0 siblings, 1 reply; 53+ messages in thread
From: Ard Biesheuvel @ 2020-05-26 6:11 UTC (permalink / raw)
To: Arvind Sankar
Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, H. Peter Anvin,
X86 ML, Nick Desaulniers, Fangrui Song, Dmitry Golovin,
clang-built-linux, Masahiro Yamada, Daniel Kiper,
Linux Kernel Mailing List
On Tue, 26 May 2020 at 00:59, Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> Add a linker script check that there are no runtime relocations, and
> remove the old one that tries to check via looking for specially-named
> sections in the object files.
>
> Drop the tests for -fPIE compiler option and -pie linker option, as they
> are available in all supported gcc and binutils versions (as well as
> clang and lld).
>
> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> ---
> arch/x86/boot/compressed/Makefile | 28 +++-----------------------
> arch/x86/boot/compressed/vmlinux.lds.S | 8 ++++++++
> 2 files changed, 11 insertions(+), 25 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index d3e882e855ee..679a2b383bfe 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -27,7 +27,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
> vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4
>
> KBUILD_CFLAGS := -m$(BITS) -O2
> -KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC)
> +KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
> KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
> cflags-$(CONFIG_X86_32) := -march=i386
> cflags-$(CONFIG_X86_64) := -mcmodel=small
> @@ -49,7 +49,7 @@ UBSAN_SANITIZE :=n
> KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
> # Compressed kernel should be built as PIE since it may be loaded at any
> # address by the bootloader.
> -KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
> +KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
Do we still need -pie linking with these changes applied?
> LDFLAGS_vmlinux := -T
>
> hostprogs := mkpiggy
> @@ -84,30 +84,8 @@ vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
> vmlinux-objs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
> vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
>
> -# The compressed kernel is built with -fPIC/-fPIE so that a boot loader
> -# can place it anywhere in memory and it will still run. However, since
> -# it is executed as-is without any ELF relocation processing performed
> -# (and has already had all relocation sections stripped from the binary),
> -# none of the code can use data relocations (e.g. static assignments of
> -# pointer values), since they will be meaningless at runtime. This check
> -# will refuse to link the vmlinux if any of these relocations are found.
> -quiet_cmd_check_data_rel = DATAREL $@
> -define cmd_check_data_rel
> - for obj in $(filter %.o,$^); do \
> - $(READELF) -S $$obj | grep -qF .rel.local && { \
> - echo "error: $$obj has data relocations!" >&2; \
> - exit 1; \
> - } || true; \
> - done
> -endef
> -
> -# We need to run two commands under "if_changed", so merge them into a
> -# single invocation.
> -quiet_cmd_check-and-link-vmlinux = LD $@
> - cmd_check-and-link-vmlinux = $(cmd_check_data_rel); $(cmd_ld)
> -
> $(obj)/vmlinux: $(vmlinux-objs-y) FORCE
> - $(call if_changed,check-and-link-vmlinux)
> + $(call if_changed,ld)
>
> OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
> $(obj)/vmlinux.bin: vmlinux FORCE
> diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
> index d826ab38a8f9..f9902c6ffe29 100644
> --- a/arch/x86/boot/compressed/vmlinux.lds.S
> +++ b/arch/x86/boot/compressed/vmlinux.lds.S
> @@ -42,6 +42,12 @@ SECTIONS
> *(.rodata.*)
> _erodata = . ;
> }
> + .rel.dyn : {
> + *(.rel.*)
> + }
> + .rela.dyn : {
> + *(.rela.*)
> + }
> .got : {
> *(.got)
> }
> @@ -83,3 +89,5 @@ ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT en
> #else
> ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!")
> #endif
> +
> +ASSERT(SIZEOF(.rel.dyn) == 0 && SIZEOF(.rela.dyn) == 0, "Unexpected runtime relocations detected!")
> --
> 2.26.2
>
^ permalink raw reply [flat|nested] 53+ messages in thread* Re: [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations
2020-05-26 6:11 ` Ard Biesheuvel
@ 2020-05-26 15:16 ` Arvind Sankar
2020-05-26 17:13 ` Fangrui Song
0 siblings, 1 reply; 53+ messages in thread
From: Arvind Sankar @ 2020-05-26 15:16 UTC (permalink / raw)
To: Ard Biesheuvel
Cc: Arvind Sankar, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Fangrui Song,
Dmitry Golovin, clang-built-linux, Masahiro Yamada, Daniel Kiper,
Linux Kernel Mailing List
On Tue, May 26, 2020 at 08:11:56AM +0200, Ard Biesheuvel wrote:
> On Tue, 26 May 2020 at 00:59, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > # Compressed kernel should be built as PIE since it may be loaded at any
> > # address by the bootloader.
> > -KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
> > +KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
>
> Do we still need -pie linking with these changes applied?
>
I think it's currently not strictly necessary -- eg the 64bit kernel
doesn't get linked as pie right now with LLD or old binutils. However,
it is safer to do so to ensure that the result remains PIC with future
versions of the linker. There are linker optimizations that can convert
certain PIC instructions when PIE is disabled. While I think they
currently all focus on eliminating indirection through the GOT (and thus
wouldn't be applicable any more), it's easy to imagine that they could
get extended to, for eg, convert
leaq foo(%rip), %rax
to
movl $foo, %eax
with some nop padding, etc.
Also, the relocation check that's being added here would only work with
PIE linking.
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations
2020-05-26 15:16 ` Arvind Sankar
@ 2020-05-26 17:13 ` Fangrui Song
2020-05-26 19:14 ` Arvind Sankar
0 siblings, 1 reply; 53+ messages in thread
From: Fangrui Song @ 2020-05-26 17:13 UTC (permalink / raw)
To: Arvind Sankar
Cc: Ard Biesheuvel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H. Peter Anvin, X86 ML, Nick Desaulniers, Dmitry Golovin,
clang-built-linux, Masahiro Yamada, Daniel Kiper,
Linux Kernel Mailing List
On 2020-05-26, Arvind Sankar wrote:
>On Tue, May 26, 2020 at 08:11:56AM +0200, Ard Biesheuvel wrote:
>> On Tue, 26 May 2020 at 00:59, Arvind Sankar <nivedita@alum.mit.edu> wrote:
>> > # Compressed kernel should be built as PIE since it may be loaded at any
>> > # address by the bootloader.
>> > -KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
>> > +KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
>>
>> Do we still need -pie linking with these changes applied?
>>
>
>I think it's currently not strictly necessary -- eg the 64bit kernel
>doesn't get linked as pie right now with LLD or old binutils. However,
>it is safer to do so to ensure that the result remains PIC with future
>versions of the linker. There are linker optimizations that can convert
>certain PIC instructions when PIE is disabled. While I think they
>currently all focus on eliminating indirection through the GOT (and thus
>wouldn't be applicable any more),
There are 3 forms described by x86-64 psABI B.2 Optimize GOTPCRELX Relocations
(1) movq foo@GOTPCREL(%rip), %reg -> leaq foo(%rip), %reg
(2) call *foo@GOTPCREL(%rip) -> nop; call foo
(3) jmp *foo@GOTPCREL(%rip) -> jmp foo; nop
ld.bfd and gold perform (1) even for R_X86_64_GOTPCREL. LLD requires R_X86_64_[REX_]GOTPCRELX
>it's easy to imagine that they could
>get extended to, for eg, convert
> leaq foo(%rip), %rax
>to
> movl $foo, %eax
>with some nop padding, etc.
Not with NOP padding, but probably with instruction prefixes. It is
unclear the rewriting will be beneficial. Rewriting instructions definitely requires a
dedicated relocation type like R_X86_64_[REX_]GOTPCRELX.
>Also, the relocation check that's being added here would only work with
>PIE linking.
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations
2020-05-26 17:13 ` Fangrui Song
@ 2020-05-26 19:14 ` Arvind Sankar
2020-08-06 11:19 ` Andy Shevchenko
0 siblings, 1 reply; 53+ messages in thread
From: Arvind Sankar @ 2020-05-26 19:14 UTC (permalink / raw)
To: Fangrui Song
Cc: Arvind Sankar, Ard Biesheuvel, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, H. Peter Anvin, X86 ML, Nick Desaulniers,
Dmitry Golovin, clang-built-linux, Masahiro Yamada, Daniel Kiper,
Linux Kernel Mailing List
On Tue, May 26, 2020 at 10:13:40AM -0700, Fangrui Song wrote:
>
> On 2020-05-26, Arvind Sankar wrote:
> >On Tue, May 26, 2020 at 08:11:56AM +0200, Ard Biesheuvel wrote:
> >> On Tue, 26 May 2020 at 00:59, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >> > # Compressed kernel should be built as PIE since it may be loaded at any
> >> > # address by the bootloader.
> >> > -KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
> >> > +KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
> >>
> >> Do we still need -pie linking with these changes applied?
> >>
> >
> >I think it's currently not strictly necessary -- eg the 64bit kernel
> >doesn't get linked as pie right now with LLD or old binutils. However,
> >it is safer to do so to ensure that the result remains PIC with future
> >versions of the linker. There are linker optimizations that can convert
> >certain PIC instructions when PIE is disabled. While I think they
> >currently all focus on eliminating indirection through the GOT (and thus
> >wouldn't be applicable any more),
>
> There are 3 forms described by x86-64 psABI B.2 Optimize GOTPCRELX Relocations
>
> (1) movq foo@GOTPCREL(%rip), %reg -> leaq foo(%rip), %reg
> (2) call *foo@GOTPCREL(%rip) -> nop; call foo
> (3) jmp *foo@GOTPCREL(%rip) -> jmp foo; nop
>
> ld.bfd and gold perform (1) even for R_X86_64_GOTPCREL. LLD requires R_X86_64_[REX_]GOTPCRELX
The psABI says (1) can be relaxed into mov $foo, %reg if PIC is disabled
and foo lives below 4Gb. Similarly for the "test and binop" cases. Such
a relaxation would produce code that's not PIC any more, and wouldn't
boot.
>
> >it's easy to imagine that they could
> >get extended to, for eg, convert
> > leaq foo(%rip), %rax
> >to
> > movl $foo, %eax
> >with some nop padding, etc.
>
> Not with NOP padding, but probably with instruction prefixes. It is
> unclear the rewriting will be beneficial. Rewriting instructions definitely requires a
> dedicated relocation type like R_X86_64_[REX_]GOTPCRELX.
It ought to be faster: according to Agner Fog's tables, upto 4x higher
throughput than the RIP-relative LEA, and movq $foo, %rax is actually
the same size.
To take a step back, there isn't any *point* in not specifying -pie
after these changes: it would be lying to the toolchain just for the
sake of lying. It is inherently fragile, and would work only because the
toolchain isn't sophisticated enough to do some optimizations.
Eg, consider that if you ask for the address of an external function,
the compiler will generate
movq f@GOTPCREL(%rip), %reg
if f has default visibility, and
leaq f(%rip), %reg
if f has hidden visibility.
If you then link without -pie, the former gets relaxed into the non-PIC
movq $f, %reg
by the BFD linker, but the latter isn't relaxed. This is a missed
optimization, which happens because there's the GOTPCRELX to tell the
linker that the first form can be relaxed, and there's no special
relaxable relocation type for the second form.
The 64-bit kernel actually contains one of these relocations, prior to
Ard's patches to add hiddden visibility for everything. It currently
works with LLD (which can't use -pie) only because LLD doesn't appear to
perform the relaxation of
movq f@GOTPCREL(%rip), %reg
all the way to
movq $f, %reg
Binutils-2.34, which does do that relaxation, produces an unbootable
kernel if you leave out the -pie.
>
> >Also, the relocation check that's being added here would only work with
> >PIE linking.
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations
2020-05-26 19:14 ` Arvind Sankar
@ 2020-08-06 11:19 ` Andy Shevchenko
2020-08-06 16:12 ` Arvind Sankar
0 siblings, 1 reply; 53+ messages in thread
From: Andy Shevchenko @ 2020-08-06 11:19 UTC (permalink / raw)
To: Arvind Sankar
Cc: Fangrui Song, Ard Biesheuvel, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, H. Peter Anvin, X86 ML, Nick Desaulniers,
Dmitry Golovin, clang-built-linux, Masahiro Yamada, Daniel Kiper,
Linux Kernel Mailing List
On Tue, May 26, 2020 at 03:14:11PM -0400, Arvind Sankar wrote:
Side question: are you going to submit a v3 of this?
Or i.o.w. what is the status of this series?
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations
2020-08-06 11:19 ` Andy Shevchenko
@ 2020-08-06 16:12 ` Arvind Sankar
0 siblings, 0 replies; 53+ messages in thread
From: Arvind Sankar @ 2020-08-06 16:12 UTC (permalink / raw)
To: Andy Shevchenko
Cc: Arvind Sankar, Fangrui Song, Ard Biesheuvel, Thomas Gleixner,
Ingo Molnar, Borislav Petkov, H. Peter Anvin, X86 ML,
Nick Desaulniers, Dmitry Golovin, clang-built-linux,
Masahiro Yamada, Daniel Kiper, Linux Kernel Mailing List
On Thu, Aug 06, 2020 at 02:19:53PM +0300, Andy Shevchenko wrote:
> On Tue, May 26, 2020 at 03:14:11PM -0400, Arvind Sankar wrote:
>
> Side question: are you going to submit a v3 of this?
> Or i.o.w. what is the status of this series?
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
The latest is v6 [0], which has some minor changes over this version and
is rebased on 5.8-rc7.
I will send out another rebase once the merge window closes.
Thanks.
[0] https://lore.kernel.org/lkml/20200731202738.2577854-1-nivedita@alum.mit.edu/
^ permalink raw reply [flat|nested] 53+ messages in thread
* Re: [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel
2020-05-24 21:28 ` [PATCH 0/4] x86/boot: Remove runtime relocations from compressed kernel Arvind Sankar
` (5 preceding siblings ...)
2020-05-25 22:59 ` [PATCH v2 4/4] x86/boot: Check that there are no runtime relocations Arvind Sankar
@ 2020-05-26 0:37 ` Fangrui Song
6 siblings, 0 replies; 53+ messages in thread
From: Fangrui Song @ 2020-05-26 0:37 UTC (permalink / raw)
To: Arvind Sankar
Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, H. Peter Anvin,
x86, Nick Desaulniers, Dmitry Golovin, clang-built-linux,
Ard Biesheuvel, Masahiro Yamada, Daniel Kiper, linux-kernel
On 2020-05-24, Arvind Sankar wrote:
>The compressed kernel currently contains bogus runtime relocations in
>the startup code in head_{32,64}.S, which are generated by the linker,
>but must not actually be processed at runtime.
>
>This generates warnings when linking with the BFD linker, and errors
>with LLD, which defaults to erroring on runtime 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 normally have
>R_X86_64_RELATIVE relocations.
>
>This series aims to get rid of these relocations. It is based on
>efi/next (efi-changes-for-v5.8), where the latest patches touch the
>head code to eliminate the global offset table.
>
>The first patch is an independent fix for LLD, to avoid an orphan
>section in arch/x86/boot/setup.elf [0].
>
>The second 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 third patch addresses a remaining issue with the BFD linker, which
>insists on generating runtime 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. 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
>runtime relocations get reintroduced. Since the GOT has been eliminated
>as well, the compressed kernel has no runtime relocations whatsoever any
>more.
>
>[0] https://lore.kernel.org/lkml/20200521152459.558081-1-nivedita@alum.mit.edu/
>
>Arvind Sankar (4):
> x86/boot: Add .text.startup to setup.ld
> x86/boot: Remove runtime relocations from .head.text code
> x86/boot: Remove runtime relocations from head_{32,64}.S
> x86/boot: Check that there are no runtime relocations
>
> arch/x86/boot/compressed/Makefile | 36 +---------
> arch/x86/boot/compressed/head_32.S | 59 +++++++--------
> arch/x86/boot/compressed/head_64.S | 99 +++++++++++++++-----------
> arch/x86/boot/compressed/mkpiggy.c | 6 ++
> arch/x86/boot/compressed/vmlinux.lds.S | 11 +++
> arch/x86/boot/setup.ld | 2 +-
> 6 files changed, 109 insertions(+), 104 deletions(-)
>
>--
>2.26.2
All 4 commits look good.
Reviewed-by: Fangrui Song <maskray@google.com>
^ permalink raw reply [flat|nested] 53+ messages in thread