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 <[email protected]>
Acked-by: Michael Ellerman <[email protected]> (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
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 <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
---
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
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 <[email protected]>
> Reviewed-by: Kees Cook <[email protected]>
> ---
> 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
Le 16/09/2022 à 21:40, Omar Sandoval a écrit :
> [Vous ne recevez pas souvent de courriers de [email protected]. 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 <[email protected]>
>> Reviewed-by: Kees Cook <[email protected]>
>> ---
>> 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
On Sat, Sep 17, 2022 at 06:31:20AM +0000, Christophe Leroy wrote:
>
>
> Le 16/09/2022 ? 21:40, Omar Sandoval a ?crit?:
> > [Vous ne recevez pas souvent de courriers de [email protected]. 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 <[email protected]>
> >> Reviewed-by: Kees Cook <[email protected]>
> >> ---
> >> 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/[email protected]/
4: https://gitlab.com/x86-psABIs/Linux-ABI
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
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.
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...