Messages in this thread | | | Date | Mon, 27 Jan 2020 15:34:38 -0800 | From | Kees Cook <> | Subject | Re: [PATCH 2/2] x86: Discard .note.gnu.property sections in vmlinux |
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On Fri, Jan 24, 2020 at 10:18:19AM -0800, 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 x86 kernel linker script only contains a signle 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 > ... > } > > which may not be incompatible with note.gnu.property sections. Since > note.gnu.property section in kernel image is unused, this patch discards > .note.gnu.property sections in kernel linker script by adding > > /DISCARD/ : { > *(.note.gnu.property) > }
I think this is happening in the wrong place? Shouldn't this be in the DISCARDS macro in include/asm-generic/vmlinux.lds.h instead?
> before .notes sections. Since .exit.text and .exit.data sections are > discarded at runtime, it undefines EXIT_TEXT and EXIT_DATA to exclude > .exit.text and .exit.data sections from default discarded sections.
This looks like a separate issue (though maybe related to DISCARDS)?
-Kees
> > Signed-off-by: H.J. Lu <hjl.tools@gmail.com> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > --- > arch/x86/kernel/vmlinux.lds.S | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S > index 3a1a819da137..6c6cc26b0177 100644 > --- a/arch/x86/kernel/vmlinux.lds.S > +++ b/arch/x86/kernel/vmlinux.lds.S > @@ -150,6 +150,11 @@ SECTIONS > _etext = .; > . = ALIGN(PAGE_SIZE); > > + /* .note.gnu.property sections should be discarded */ > + /DISCARD/ : { > + *(.note.gnu.property) > + } > + > X86_ALIGN_RODATA_BEGIN > RO_DATA(PAGE_SIZE) > X86_ALIGN_RODATA_END > @@ -413,6 +418,12 @@ SECTIONS > STABS_DEBUG > DWARF_DEBUG > > + /* Sections to be discarded. EXIT_TEXT and EXIT_DATA discard at runtime. > + * not link time. */ > +#undef EXIT_TEXT > +#define EXIT_TEXT > +#undef EXIT_DATA > +#define EXIT_DATA > DISCARDS > /DISCARD/ : { > *(.eh_frame) > -- > 2.24.1 >
-- Kees Cook
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