[PATCH 1/2] powerpc: Keep .rela* sections when CONFIG_RELOCATABLE is defined

[PATCH 1/2] powerpc: Keep .rela* sections when CONFIG_RELOCATABLE is defined

[H.J. Lu]

arch/powerpc/kernel/vmlinux.lds.S has

 #ifdef CONFIG_RELOCATABLE
 ...
        .rela.dyn : AT(ADDR(.rela.dyn) - LOAD_OFFSET)
        {
                __rela_dyn_start = .;
                *(.rela*)
        }
 #endif
 ...
        DISCARDS
        /DISCARD/ : {
                *(*.EMB.apuinfo)
                *(.glink .iplt .plt .rela* .comment)
                *(.gnu.version*)
                *(.gnu.attributes)
                *(.eh_frame)
        }

Since .rela* sections are needed when CONFIG_RELOCATABLE is defined,
don't discard .rela* sections if CONFIG_RELOCATABLE is defined.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
---
 arch/powerpc/kernel/vmlinux.lds.S | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 31a0f201fb6f..4ba07734a210 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -366,9 +366,12 @@ SECTIONS
 	DISCARDS
 	/DISCARD/ : {
 		*(*.EMB.apuinfo)
-		*(.glink .iplt .plt .rela* .comment)
+		*(.glink .iplt .plt .comment)
 		*(.gnu.version*)
 		*(.gnu.attributes)
 		*(.eh_frame)
+#ifndef CONFIG_RELOCATABLE
+		*(.rela*)
+#endif
 	}
 }
-- 
2.25.4

[PATCH 1/2] powerpc: Keep .rela* sections when CONFIG_RELOCATABLE is defined

[H.J. Lu]

arch/powerpc/kernel/vmlinux.lds.S has

 #ifdef CONFIG_RELOCATABLE
 ...
        .rela.dyn : AT(ADDR(.rela.dyn) - LOAD_OFFSET)
        {
                __rela_dyn_start = .;
                *(.rela*)
        }
 #endif
 ...
        DISCARDS
        /DISCARD/ : {
                *(*.EMB.apuinfo)
                *(.glink .iplt .plt .rela* .comment)
                *(.gnu.version*)
                *(.gnu.attributes)
                *(.eh_frame)
        }

Since .rela* sections are needed when CONFIG_RELOCATABLE is defined,
don't discard .rela* sections if CONFIG_RELOCATABLE is defined.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
---
 arch/powerpc/kernel/vmlinux.lds.S | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 31a0f201fb6f..4ba07734a210 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -366,9 +366,12 @@ SECTIONS
 	DISCARDS
 	/DISCARD/ : {
 		*(*.EMB.apuinfo)
-		*(.glink .iplt .plt .rela* .comment)
+		*(.glink .iplt .plt .comment)
 		*(.gnu.version*)
 		*(.gnu.attributes)
 		*(.eh_frame)
+#ifndef CONFIG_RELOCATABLE
+		*(.rela*)
+#endif
 	}
 }
-- 
2.25.4

[PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[H.J. Lu]

With the command-line option, -mx86-used-note=yes, the x86 assembler
in binutils 2.32 and above generates a program property note in a note
section, .note.gnu.property, to encode used x86 ISAs and features.  But
kernel linker script only contains a single NOTE segment:

PHDRS {
 text PT_LOAD FLAGS(5);
 data PT_LOAD FLAGS(6);
 percpu PT_LOAD FLAGS(6);
 init PT_LOAD FLAGS(7);
 note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
 .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}

The NOTE segment generated by kernel linker script is aligned to 4 bytes.
But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
we get

[hjl@gnu-skx-1 linux]$ readelf -n vmlinux

Displaying notes found in: .notes
  Owner                Data size Description
  Xen                  0x00000006 Unknown note type: (0x00000006)
   description data: 6c 69 6e 75 78 00
  Xen                  0x00000004 Unknown note type: (0x00000007)
   description data: 32 2e 36 00
  xen-3.0              0x00000005 Unknown note type: (0x006e6558)
   description data: 08 00 00 00 03
readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
0x80000000, alignment: 8
[hjl@gnu-skx-1 linux]$

Since note.gnu.property section in kernel image is never used, this patch
discards .note.gnu.property sections in kernel linker script by adding

/DISCARD/ : {
  *(.note.gnu.property)
}

before kernel NOTE segment in generic NOTES.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 include/asm-generic/vmlinux.lds.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 71e387a5fe90..95cd678428f4 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -833,7 +833,14 @@
 #define TRACEDATA
 #endif
 
+/*
+ * Discard .note.gnu.property sections which are unused and have
+ * different alignment requirement from kernel note sections.
+ */
 #define NOTES								\
+	/DISCARD/ : {							\
+		*(.note.gnu.property)					\
+	}								\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
 		__start_notes = .;					\
 		KEEP(*(.note.*))					\
-- 
2.25.4

[PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[H.J. Lu]

With the command-line option, -mx86-used-note=yes, the x86 assembler
in binutils 2.32 and above generates a program property note in a note
section, .note.gnu.property, to encode used x86 ISAs and features.  But
kernel linker script only contains a single NOTE segment:

PHDRS {
 text PT_LOAD FLAGS(5);
 data PT_LOAD FLAGS(6);
 percpu PT_LOAD FLAGS(6);
 init PT_LOAD FLAGS(7);
 note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
 .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}

The NOTE segment generated by kernel linker script is aligned to 4 bytes.
But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
we get

[hjl@gnu-skx-1 linux]$ readelf -n vmlinux

Displaying notes found in: .notes
  Owner                Data size Description
  Xen                  0x00000006 Unknown note type: (0x00000006)
   description data: 6c 69 6e 75 78 00
  Xen                  0x00000004 Unknown note type: (0x00000007)
   description data: 32 2e 36 00
  xen-3.0              0x00000005 Unknown note type: (0x006e6558)
   description data: 08 00 00 00 03
readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
0x80000000, alignment: 8
[hjl@gnu-skx-1 linux]$

Since note.gnu.property section in kernel image is never used, this patch
discards .note.gnu.property sections in kernel linker script by adding

/DISCARD/ : {
  *(.note.gnu.property)
}

before kernel NOTE segment in generic NOTES.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 include/asm-generic/vmlinux.lds.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 71e387a5fe90..95cd678428f4 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -833,7 +833,14 @@
 #define TRACEDATA
 #endif
 
+/*
+ * Discard .note.gnu.property sections which are unused and have
+ * different alignment requirement from kernel note sections.
+ */
 #define NOTES								\
+	/DISCARD/ : {							\
+		*(.note.gnu.property)					\
+	}								\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
 		__start_notes = .;					\
 		KEEP(*(.note.*))					\
-- 
2.25.4

Re: [PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[Omar Sandoval]

On Tue, Apr 28, 2020 at 06:21:05AM -0700, H.J. Lu wrote:
> With the command-line option, -mx86-used-note=yes, the x86 assembler
> in binutils 2.32 and above generates a program property note in a note
> section, .note.gnu.property, to encode used x86 ISAs and features.  But
> kernel linker script only contains a single NOTE segment:
> 
> PHDRS {
>  text PT_LOAD FLAGS(5);
>  data PT_LOAD FLAGS(6);
>  percpu PT_LOAD FLAGS(6);
>  init PT_LOAD FLAGS(7);
>  note PT_NOTE FLAGS(0);
> }
> SECTIONS
> {
> ...
>  .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
> e.*)) __stop_notes = .; } :text :note
> ...
> }
> 
> The NOTE segment generated by kernel linker script is aligned to 4 bytes.
> But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
> we get
> 
> [hjl@gnu-skx-1 linux]$ readelf -n vmlinux
> 
> Displaying notes found in: .notes
>   Owner                Data size Description
>   Xen                  0x00000006 Unknown note type: (0x00000006)
>    description data: 6c 69 6e 75 78 00
>   Xen                  0x00000004 Unknown note type: (0x00000007)
>    description data: 32 2e 36 00
>   xen-3.0              0x00000005 Unknown note type: (0x006e6558)
>    description data: 08 00 00 00 03
> readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
> readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
> 0x80000000, alignment: 8
> [hjl@gnu-skx-1 linux]$
> 
> Since note.gnu.property section in kernel image is never used, this patch
> discards .note.gnu.property sections in kernel linker script by adding
> 
> /DISCARD/ : {
>   *(.note.gnu.property)
> }
> 
> before kernel NOTE segment in generic NOTES.
> 
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> ---
>  include/asm-generic/vmlinux.lds.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 71e387a5fe90..95cd678428f4 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -833,7 +833,14 @@
>  #define TRACEDATA
>  #endif
>  
> +/*
> + * Discard .note.gnu.property sections which are unused and have
> + * different alignment requirement from kernel note sections.
> + */
>  #define NOTES								\
> +	/DISCARD/ : {							\
> +		*(.note.gnu.property)					\
> +	}								\
>  	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
>  		__start_notes = .;					\
>  		KEEP(*(.note.*))					\
> -- 
> 2.25.4
> 

Hi, H.J.,

I recently ran into this same .notes corruption when building kernels on
Arch Linux.

What ended up happening to this patch? It doesn't appear to have been
merged, and I couldn't find any further discussion about it. I'm happy
to resend it for you if you need a hand.

Thanks,
Omar

Re: [PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[Christophe Leroy]

Le 16/09/2022 à 21:40, Omar Sandoval a écrit :
> [Vous ne recevez pas souvent de courriers de osandov@osandov.com. D?couvrez pourquoi ceci est important ? https://aka.ms/LearnAboutSenderIdentification ]
> 
> On Tue, Apr 28, 2020 at 06:21:05AM -0700, H.J. Lu wrote:
>> With the command-line option, -mx86-used-note=yes, the x86 assembler
>> in binutils 2.32 and above generates a program property note in a note
>> section, .note.gnu.property, to encode used x86 ISAs and features.  But
>> kernel linker script only contains a single NOTE segment:
>>
>> PHDRS {
>>   text PT_LOAD FLAGS(5);
>>   data PT_LOAD FLAGS(6);
>>   percpu PT_LOAD FLAGS(6);
>>   init PT_LOAD FLAGS(7);
>>   note PT_NOTE FLAGS(0);
>> }
>> SECTIONS
>> {
>> ...
>>   .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
>> e.*)) __stop_notes = .; } :text :note
>> ...
>> }
>>
>> The NOTE segment generated by kernel linker script is aligned to 4 bytes.
>> But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
>> we get
>>
>> [hjl@gnu-skx-1 linux]$ readelf -n vmlinux
>>
>> Displaying notes found in: .notes
>>    Owner                Data size Description
>>    Xen                  0x00000006 Unknown note type: (0x00000006)
>>     description data: 6c 69 6e 75 78 00
>>    Xen                  0x00000004 Unknown note type: (0x00000007)
>>     description data: 32 2e 36 00
>>    xen-3.0              0x00000005 Unknown note type: (0x006e6558)
>>     description data: 08 00 00 00 03
>> readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
>> readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
>> 0x80000000, alignment: 8
>> [hjl@gnu-skx-1 linux]$
>>
>> Since note.gnu.property section in kernel image is never used, this patch
>> discards .note.gnu.property sections in kernel linker script by adding
>>
>> /DISCARD/ : {
>>    *(.note.gnu.property)
>> }
>>
>> before kernel NOTE segment in generic NOTES.
>>
>> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
>> Reviewed-by: Kees Cook <keescook@chromium.org>
>> ---
>>   include/asm-generic/vmlinux.lds.h | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
>> index 71e387a5fe90..95cd678428f4 100644
>> --- a/include/asm-generic/vmlinux.lds.h
>> +++ b/include/asm-generic/vmlinux.lds.h
>> @@ -833,7 +833,14 @@
>>   #define TRACEDATA
>>   #endif
>>
>> +/*
>> + * Discard .note.gnu.property sections which are unused and have
>> + * different alignment requirement from kernel note sections.
>> + */
>>   #define NOTES                                                                \
>> +     /DISCARD/ : {                                                   \
>> +             *(.note.gnu.property)                                   \
>> +     }                                                               \
>>        .notes : AT(ADDR(.notes) - LOAD_OFFSET) {                       \
>>                __start_notes = .;                                      \
>>                KEEP(*(.note.*))                                        \
>> --
>> 2.25.4
>>
> 
> Hi, H.J.,
> 
> I recently ran into this same .notes corruption when building kernels on
> Arch Linux.
> 
> What ended up happening to this patch? It doesn't appear to have been
> merged, and I couldn't find any further discussion about it. I'm happy
> to resend it for you if you need a hand.

As far as I can see, ARM64 is doing something with that section, see 
arch/arm64/include/asm/assembler.h

Instead of discarding that section, would it be enough to force 
alignment of .notes to 8 bytes ?

Thanks
Christophe


> 
> Thanks,
> Omar

Re: [PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[Omar Sandoval]

On Sat, Sep 17, 2022 at 06:31:20AM +0000, Christophe Leroy wrote:
> 
> 
> Le 16/09/2022 à 21:40, Omar Sandoval a écrit :
> > [Vous ne recevez pas souvent de courriers de osandov@osandov.com. D?couvrez pourquoi ceci est important ? https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > On Tue, Apr 28, 2020 at 06:21:05AM -0700, H.J. Lu wrote:
> >> With the command-line option, -mx86-used-note=yes, the x86 assembler
> >> in binutils 2.32 and above generates a program property note in a note
> >> section, .note.gnu.property, to encode used x86 ISAs and features.  But
> >> kernel linker script only contains a single NOTE segment:
> >>
> >> PHDRS {
> >>   text PT_LOAD FLAGS(5);
> >>   data PT_LOAD FLAGS(6);
> >>   percpu PT_LOAD FLAGS(6);
> >>   init PT_LOAD FLAGS(7);
> >>   note PT_NOTE FLAGS(0);
> >> }
> >> SECTIONS
> >> {
> >> ...
> >>   .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
> >> e.*)) __stop_notes = .; } :text :note
> >> ...
> >> }
> >>
> >> The NOTE segment generated by kernel linker script is aligned to 4 bytes.
> >> But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
> >> we get
> >>
> >> [hjl@gnu-skx-1 linux]$ readelf -n vmlinux
> >>
> >> Displaying notes found in: .notes
> >>    Owner                Data size Description
> >>    Xen                  0x00000006 Unknown note type: (0x00000006)
> >>     description data: 6c 69 6e 75 78 00
> >>    Xen                  0x00000004 Unknown note type: (0x00000007)
> >>     description data: 32 2e 36 00
> >>    xen-3.0              0x00000005 Unknown note type: (0x006e6558)
> >>     description data: 08 00 00 00 03
> >> readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
> >> readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
> >> 0x80000000, alignment: 8
> >> [hjl@gnu-skx-1 linux]$
> >>
> >> Since note.gnu.property section in kernel image is never used, this patch
> >> discards .note.gnu.property sections in kernel linker script by adding
> >>
> >> /DISCARD/ : {
> >>    *(.note.gnu.property)
> >> }
> >>
> >> before kernel NOTE segment in generic NOTES.
> >>
> >> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> >> Reviewed-by: Kees Cook <keescook@chromium.org>
> >> ---
> >>   include/asm-generic/vmlinux.lds.h | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> >> index 71e387a5fe90..95cd678428f4 100644
> >> --- a/include/asm-generic/vmlinux.lds.h
> >> +++ b/include/asm-generic/vmlinux.lds.h
> >> @@ -833,7 +833,14 @@
> >>   #define TRACEDATA
> >>   #endif
> >>
> >> +/*
> >> + * Discard .note.gnu.property sections which are unused and have
> >> + * different alignment requirement from kernel note sections.
> >> + */
> >>   #define NOTES                                                                \
> >> +     /DISCARD/ : {                                                   \
> >> +             *(.note.gnu.property)                                   \
> >> +     }                                                               \
> >>        .notes : AT(ADDR(.notes) - LOAD_OFFSET) {                       \
> >>                __start_notes = .;                                      \
> >>                KEEP(*(.note.*))                                        \
> >> --
> >> 2.25.4
> >>
> > 
> > Hi, H.J.,
> > 
> > I recently ran into this same .notes corruption when building kernels on
> > Arch Linux.
> > 
> > What ended up happening to this patch? It doesn't appear to have been
> > merged, and I couldn't find any further discussion about it. I'm happy
> > to resend it for you if you need a hand.
> 
> As far as I can see, ARM64 is doing something with that section, see 
> arch/arm64/include/asm/assembler.h
> 
> Instead of discarding that section, would it be enough to force 
> alignment of .notes to 8 bytes ?
> 
> Thanks
> Christophe

Unfortunately, "alignment requirement" here isn't just the starting
alignment of the .notes section; it also refers to internal padding in
the note metadata to keep things aligned. Changing this would break
anyone who parses /sys/kernel/notes (e.g., perf).

Here is a little more context around this mess:

The System V gABI [1] says that the note header and descriptor should be
aligned to 4 bytes for 32-bit files and 8 bytes for 64-bit files.
However, Linux never followed this, and 4-byte alignment is used for
both 32-bit and 64-bit files; see elf(5) [2].

The only exception as of 2022 is
.note.gnu.property/NT_GNU_PROPERTY_TYPE_0, which is defined to follow
the gABI alignment. There was a long thread discussing this back in 2018
with the subject "PT_NOTE alignment, NT_GNU_PROPERTY_TYPE_0, glibc and
gold" [3].

According to the gABI Linux Extensions [4], consumers are now supposed
to use the p_align of the PT_NOTE segment instead of assuming an
alignment.

There are a few issues with this for the kernel:

* The vmlinux linker script squishes together all of the notes sections
  with different alignments without adjusting their internal padding,
  but sets p_align to the maximum required alignment. This is what
  confuses readelf and co: they expect 8-byte alignment, but most of the
  note entries are only padded for 4-byte alignment.
* The vmlinux .notes section is exported as /sys/kernel/notes. This is
  stable ABI and has always had 4-byte alignment; all existing parsers
  assume this.
* /sys/kernel/notes doesn't currently have a way to specify an alternate
  alignment anyways.

My suggestion would be to keep .note.gnu.property in its own section in
vmlinux, or create a new .notes8 section with 8-byte alignment, and
leave .notes and /sys/kernel/notes alone.

I'm not sure what exactly arch/arm64/include/asm/assembler.h is doing
with this file. Perhaps the author, Mark Brown, can clarify?

1: http://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section
2: https://man7.org/linux/man-pages/man5/elf.5.html#:~:text=Notes%20(Nhdr)
3: https://public-inbox.org/libc-alpha/13a92cb0-a993-f684-9a96-e02e4afb1bef@redhat.com/
4: https://gitlab.com/x86-psABIs/Linux-ABI

Re: [PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 693 bytes --]

On Mon, Sep 19, 2022 at 10:26:17AM -0700, Omar Sandoval wrote:

In general if you're going to CC someone into a thread please put
a note at the start of your mail explaining why, many of us get
copied on a lot of irrelevant things for no apparently reason so
if it's not immediately obvious why we were sent a mail there's
every chance it'll just be deleted.

> I'm not sure what exactly arch/arm64/include/asm/assembler.h is doing
> with this file. Perhaps the author, Mark Brown, can clarify?

I don't understand the question, what file are you talking about
here?  arch/arm64/include/asm/assembler.h is itself a file and I
couldn't find anything nearby in your mail talking about a file...

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[Omar Sandoval]

On Mon, Sep 19, 2022 at 06:33:40PM +0100, Mark Brown wrote:
> On Mon, Sep 19, 2022 at 10:26:17AM -0700, Omar Sandoval wrote:
> 
> In general if you're going to CC someone into a thread please put
> a note at the start of your mail explaining why, many of us get
> copied on a lot of irrelevant things for no apparently reason so
> if it's not immediately obvious why we were sent a mail there's
> every chance it'll just be deleted.

Sorry about that.

> > I'm not sure what exactly arch/arm64/include/asm/assembler.h is doing
> > with this file. Perhaps the author, Mark Brown, can clarify?
> 
> I don't understand the question, what file are you talking about
> here?  arch/arm64/include/asm/assembler.h is itself a file and I
> couldn't find anything nearby in your mail talking about a file...

Oops, that was a typo, I meant to say "I'm not sure what
arch/arm64/include/asm/assembler.h is doing with this *note*". To be
more explicit: does ARM64 need .note.gnu.property/NT_GNU_PROPERTY_TYPE_0
in vmlinux?

Thanks,
Omar

Re: [PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[Mark Brown]

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On Mon, Sep 19, 2022 at 10:40:36AM -0700, Omar Sandoval wrote:
> On Mon, Sep 19, 2022 at 06:33:40PM +0100, Mark Brown wrote:

> > I don't understand the question, what file are you talking about
> > here?  arch/arm64/include/asm/assembler.h is itself a file and I
> > couldn't find anything nearby in your mail talking about a file...

> Oops, that was a typo, I meant to say "I'm not sure what
> arch/arm64/include/asm/assembler.h is doing with this *note*". To be
> more explicit: does ARM64 need .note.gnu.property/NT_GNU_PROPERTY_TYPE_0
> in vmlinux?

It needs it in at least the vDSO which gets built into vmlinux.
AFAIR we don't use it in normal kernel code.

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[PATCH 1/2] powerpc: Discard .rela* sections if CONFIG_RELOCATABLE is undefined

[H.J. Lu]

arch/powerpc/kernel/vmlinux.lds.S has

        DISCARDS
        /DISCARD/ : {
                *(*.EMB.apuinfo)
                *(.glink .iplt .plt .rela* .comment)
                *(.gnu.version*)
                *(.gnu.attributes)
                *(.eh_frame)
        }

Since .rela* sections are needed when CONFIG_RELOCATABLE is defined,
change to discard .rela* sections if CONFIG_RELOCATABLE is undefined.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
---
 arch/powerpc/kernel/vmlinux.lds.S | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 31a0f201fb6f..4ba07734a210 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -366,9 +366,12 @@ SECTIONS
 	DISCARDS
 	/DISCARD/ : {
 		*(*.EMB.apuinfo)
-		*(.glink .iplt .plt .rela* .comment)
+		*(.glink .iplt .plt .comment)
 		*(.gnu.version*)
 		*(.gnu.attributes)
 		*(.eh_frame)
+#ifndef CONFIG_RELOCATABLE
+		*(.rela*)
+#endif
 	}
 }
-- 
2.25.4

[PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[H.J. Lu]

With the command-line option, -mx86-used-note=yes, the x86 assembler
in binutils 2.32 and above generates a program property note in a note
section, .note.gnu.property, to encode used x86 ISAs and features.  But
kernel linker script only contains a single NOTE segment:

PHDRS {
 text PT_LOAD FLAGS(5);
 data PT_LOAD FLAGS(6);
 percpu PT_LOAD FLAGS(6);
 init PT_LOAD FLAGS(7);
 note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
 .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}

The NOTE segment generated by kernel linker script is aligned to 4 bytes.
But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
we get

[hjl@gnu-skx-1 linux]$ readelf -n vmlinux

Displaying notes found in: .notes
  Owner                Data size Description
  Xen                  0x00000006 Unknown note type: (0x00000006)
   description data: 6c 69 6e 75 78 00
  Xen                  0x00000004 Unknown note type: (0x00000007)
   description data: 32 2e 36 00
  xen-3.0              0x00000005 Unknown note type: (0x006e6558)
   description data: 08 00 00 00 03
readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
0x80000000, alignment: 8
[hjl@gnu-skx-1 linux]$

Since note.gnu.property section in kernel image is never used, this patch
discards .note.gnu.property sections in kernel linker script by adding

/DISCARD/ : {
  *(.note.gnu.property)
}

before kernel NOTE segment in generic NOTES.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 include/asm-generic/vmlinux.lds.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 71e387a5fe90..95cd678428f4 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -833,7 +833,14 @@
 #define TRACEDATA
 #endif
 
+/*
+ * Discard .note.gnu.property sections which are unused and have
+ * different alignment requirement from kernel note sections.
+ */
 #define NOTES								\
+	/DISCARD/ : {							\
+		*(.note.gnu.property)					\
+	}								\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
 		__start_notes = .;					\
 		KEEP(*(.note.*))					\
-- 
2.25.4

[PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[H.J. Lu]

With the command-line option, -mx86-used-note=yes, the x86 assembler
in binutils 2.32 and above generates a program property note in a note
section, .note.gnu.property, to encode used x86 ISAs and features.  But
kernel linker script only contains a single NOTE segment:

PHDRS {
 text PT_LOAD FLAGS(5);
 data PT_LOAD FLAGS(6);
 percpu PT_LOAD FLAGS(6);
 init PT_LOAD FLAGS(7);
 note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
 .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}

The NOTE segment generated by kernel linker script is aligned to 4 bytes.
But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
we get

[hjl@gnu-skx-1 linux]$ readelf -n vmlinux

Displaying notes found in: .notes
  Owner                Data size Description
  Xen                  0x00000006 Unknown note type: (0x00000006)
   description data: 6c 69 6e 75 78 00
  Xen                  0x00000004 Unknown note type: (0x00000007)
   description data: 32 2e 36 00
  xen-3.0              0x00000005 Unknown note type: (0x006e6558)
   description data: 08 00 00 00 03
readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
0x80000000, alignment: 8
[hjl@gnu-skx-1 linux]$

Since note.gnu.property section in kernel image is never used, this patch
discards .note.gnu.property sections in kernel linker script by adding

/DISCARD/ : {
  *(.note.gnu.property)
}

before kernel NOTE segment in generic NOTES.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 include/asm-generic/vmlinux.lds.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 71e387a5fe90..95cd678428f4 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -833,7 +833,14 @@
 #define TRACEDATA
 #endif
 
+/*
+ * Discard .note.gnu.property sections which are unused and have
+ * different alignment requirement from kernel note sections.
+ */
 #define NOTES								\
+	/DISCARD/ : {							\
+		*(.note.gnu.property)					\
+	}								\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
 		__start_notes = .;					\
 		KEEP(*(.note.*))					\
-- 
2.25.4

[PATCH 1/2] Add RUNTIME_DISCARD_EXIT to generic DISCARDS

[H.J. Lu]

In x86 kernel, .exit.text and .exit.data sections are discarded at
runtime, not by linker.  Add RUNTIME_DISCARD_EXIT to generic DISCARDS
and define it in x86 kernel linker script to keep them.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/kernel/vmlinux.lds.S     |  1 +
 include/asm-generic/vmlinux.lds.h | 10 ++++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index e3296aa028fe..7206e1ac23dd 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -21,6 +21,7 @@
 #define LOAD_OFFSET __START_KERNEL_map
 #endif
 
+#define RUNTIME_DISCARD_EXIT
 #define EMITS_PT_NOTE
 #define RO_EXCEPTION_TABLE_ALIGN	16
 
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e00f41aa8ec4..6b943fb8c5fd 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -894,10 +894,16 @@
  * section definitions so that such archs put those in earlier section
  * definitions.
  */
+#ifdef RUNTIME_DISCARD_EXIT
+#define EXIT_DISCARDS
+#else
+#define EXIT_DISCARDS							\
+	EXIT_TEXT							\
+	EXIT_DATA
+#endif
 #define DISCARDS							\
 	/DISCARD/ : {							\
-	EXIT_TEXT							\
-	EXIT_DATA							\
+	EXIT_DISCARDS							\
 	EXIT_CALL							\
 	*(.discard)							\
 	*(.discard.*)							\
-- 
2.25.1

[PATCH 2/2] Discard .note.gnu.property sections in generic NOTES

[H.J. Lu]

With the command-line option, -mx86-used-note=yes, the x86 assembler
in binutils 2.32 and above generates a program property note in a note
section, .note.gnu.property, to encode used x86 ISAs and features.  But
kernel linker script only contains a single NOTE segment:

PHDRS {
 text PT_LOAD FLAGS(5);
 data PT_LOAD FLAGS(6);
 percpu PT_LOAD FLAGS(6);
 init PT_LOAD FLAGS(7);
 note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
 .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}

The NOTE segment generated by kernel linker script is aligned to 4 bytes.
But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
we get

[hjl@gnu-skx-1 linux]$ readelf -n vmlinux

Displaying notes found in: .notes
  Owner                Data size Description
  Xen                  0x00000006 Unknown note type: (0x00000006)
   description data: 6c 69 6e 75 78 00
  Xen                  0x00000004 Unknown note type: (0x00000007)
   description data: 32 2e 36 00
  xen-3.0              0x00000005 Unknown note type: (0x006e6558)
   description data: 08 00 00 00 03
readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
0x80000000, alignment: 8
[hjl@gnu-skx-1 linux]$

Since note.gnu.property section in kernel image is never used, this patch
discards .note.gnu.property sections in kernel linker script by adding

/DISCARD/ : {
  *(.note.gnu.property)
}

before kernel NOTE segment in generic NOTES.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 include/asm-generic/vmlinux.lds.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 6b943fb8c5fd..6659a7c07c84 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -818,7 +818,14 @@
 #define TRACEDATA
 #endif
 
+/*
+ * Discard .note.gnu.property sections which are unused and have
+ * different alignment requirement from kernel note sections.
+ */
 #define NOTES								\
+	/DISCARD/ : {							\
+		*(.note.gnu.property)					\
+	}								\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
 		__start_notes = .;					\
 		KEEP(*(.note.*))					\
-- 
2.25.1