* [PATCH] x86, vmlinux.lds: Page-Align end of ..page_aligned sections
@ 2020-07-21 9:34 Joerg Roedel
2020-07-21 18:44 ` Kees Cook
0 siblings, 1 reply; 4+ messages in thread
From: Joerg Roedel @ 2020-07-21 9:34 UTC (permalink / raw)
To: x86
Cc: hpa, Arnd Bergmann, Kees Cook, Heiko Carstens, Joerg Roedel,
Bob Haarman, hjl.tools, Arvind Sankar, Dmitry Safonov,
linux-kernel, linux-arch
From: Joerg Roedel <jroedel@suse.de>
Align the end of the .bss..page_aligned and .data..page_aligned section
on page-size too. Otherwise the linker might place other objects on the
page of the last ..page_aligned object. This is inconsistent with other
objects in those sections, which all have their own page.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/kernel/vmlinux.lds.S | 1 +
include/asm-generic/vmlinux.lds.h | 4 +++-
2 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3bfc8dd8a43d..9a03e5b23135 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -358,6 +358,7 @@ SECTIONS
.bss : AT(ADDR(.bss) - LOAD_OFFSET) {
__bss_start = .;
*(.bss..page_aligned)
+ . = ALIGN(PAGE_SIZE);
*(BSS_MAIN)
BSS_DECRYPTED
. = ALIGN(PAGE_SIZE);
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 3ceb4b7279ec..bd6302bd1d0f 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -360,7 +360,8 @@
#define PAGE_ALIGNED_DATA(page_align) \
. = ALIGN(page_align); \
- *(.data..page_aligned)
+ *(.data..page_aligned) \
+ . = ALIGN(page_align);
#define READ_MOSTLY_DATA(align) \
. = ALIGN(align); \
@@ -758,6 +759,7 @@
.bss : AT(ADDR(.bss) - LOAD_OFFSET) { \
BSS_FIRST_SECTIONS \
*(.bss..page_aligned) \
+ . = ALIGN(PAGE_SIZE); \
*(.dynbss) \
*(BSS_MAIN) \
*(COMMON) \
--
2.27.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] x86, vmlinux.lds: Page-Align end of ..page_aligned sections
2020-07-21 9:34 [PATCH] x86, vmlinux.lds: Page-Align end of ..page_aligned sections Joerg Roedel
@ 2020-07-21 18:44 ` Kees Cook
2020-07-21 20:05 ` Thomas Gleixner
0 siblings, 1 reply; 4+ messages in thread
From: Kees Cook @ 2020-07-21 18:44 UTC (permalink / raw)
To: Joerg Roedel
Cc: x86, hpa, Arnd Bergmann, Heiko Carstens, Joerg Roedel,
Bob Haarman, hjl.tools, Arvind Sankar, Dmitry Safonov,
linux-kernel, linux-arch
On Tue, Jul 21, 2020 at 11:34:48AM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> Align the end of the .bss..page_aligned and .data..page_aligned section
> on page-size too. Otherwise the linker might place other objects on the
> page of the last ..page_aligned object. This is inconsistent with other
> objects in those sections, which all have their own page.
What problem was actually encountered? (i.e. why is it a problem for the
other data to be in the page of the page-aligned data? shouldn't those
data have their own, separate, alignment hint?)
--
Kees Cook
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86, vmlinux.lds: Page-Align end of ..page_aligned sections
2020-07-21 18:44 ` Kees Cook
@ 2020-07-21 20:05 ` Thomas Gleixner
2020-07-21 21:18 ` Kees Cook
0 siblings, 1 reply; 4+ messages in thread
From: Thomas Gleixner @ 2020-07-21 20:05 UTC (permalink / raw)
To: Kees Cook, Joerg Roedel
Cc: x86, hpa, Arnd Bergmann, Heiko Carstens, Joerg Roedel,
Bob Haarman, hjl.tools, Arvind Sankar, Dmitry Safonov,
linux-kernel, linux-arch
Kees,
Kees Cook <keescook@chromium.org> writes:
> On Tue, Jul 21, 2020 at 11:34:48AM +0200, Joerg Roedel wrote:
>> From: Joerg Roedel <jroedel@suse.de>
>>
>> Align the end of the .bss..page_aligned and .data..page_aligned section
>> on page-size too. Otherwise the linker might place other objects on the
>> page of the last ..page_aligned object. This is inconsistent with other
>> objects in those sections, which all have their own page.
>
> What problem was actually encountered? (i.e. why is it a problem for the
> other data to be in the page of the page-aligned data? shouldn't those
> data have their own, separate, alignment hint?)
See: lore.kernel.org/r/87sgdmm8u4.fsf@nanos.tec.linutronix.de
Thanks,
tglx
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] x86, vmlinux.lds: Page-Align end of ..page_aligned sections
2020-07-21 20:05 ` Thomas Gleixner
@ 2020-07-21 21:18 ` Kees Cook
0 siblings, 0 replies; 4+ messages in thread
From: Kees Cook @ 2020-07-21 21:18 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Joerg Roedel, x86, hpa, Arnd Bergmann, Heiko Carstens,
Joerg Roedel, Bob Haarman, hjl.tools, Arvind Sankar,
Dmitry Safonov, linux-kernel, linux-arch
On Tue, Jul 21, 2020 at 10:05:05PM +0200, Thomas Gleixner wrote:
> Kees,
>
> Kees Cook <keescook@chromium.org> writes:
> > On Tue, Jul 21, 2020 at 11:34:48AM +0200, Joerg Roedel wrote:
> >> From: Joerg Roedel <jroedel@suse.de>
> >>
> >> Align the end of the .bss..page_aligned and .data..page_aligned section
> >> on page-size too. Otherwise the linker might place other objects on the
> >> page of the last ..page_aligned object. This is inconsistent with other
> >> objects in those sections, which all have their own page.
> >
> > What problem was actually encountered? (i.e. why is it a problem for the
> > other data to be in the page of the page-aligned data? shouldn't those
> > data have their own, separate, alignment hint?)
>
> See: lore.kernel.org/r/87sgdmm8u4.fsf@nanos.tec.linutronix.de
Ah-ha: "But with explicit sections which store only page aligned objects
there is an implicit guarantee that the object is alone in the page
in which it is placed. That works for all objects except the last
one. That's inconsistent."
Understood now. The bit in this commit log for "which all have their own
page" wasn't clear to me about _why_ (it was coming from .page_aligned,
which means both aligned and dedicated).
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-07-21 9:34 [PATCH] x86, vmlinux.lds: Page-Align end of ..page_aligned sections Joerg Roedel
2020-07-21 18:44 ` Kees Cook
2020-07-21 20:05 ` Thomas Gleixner
2020-07-21 21:18 ` Kees Cook
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