Re: [PATCH 11/70] x86/boot/compressed/64: Disable red-zone usage

Borislav Petkov
2020-03-31T13:16:16Z

On Thu, Mar 19, 2020 at 10:13:08AM +0100, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> The x86-64 ABI defines a red-zone on the stack:
>
> The 128-byte area beyond the location pointed to by %rsp is
> considered to be reserved and shall not be modified by signal or
> interrupt handlers. 10 Therefore, functions may use this area for
^^

That 10 is the footnote number from the pdf. :)

> temporary data that is not needed across function calls. In
> particular, leaf functions may use this area for their entire stack
> frame, rather than adjusting the stack pointer in the prologue and
> epilogue. This area is known as the red zone.
>
> This is not compatible with exception handling, so disable it for the

I could use some blurb as to what the problem is, for future reference.

> pre-decompression boot code.
>
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> arch/x86/boot/Makefile | 2 +-
> arch/x86/boot/compressed/Makefile | 4 ++--
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> index 012b82fc8617..8f55e4ce1ccc 100644
> --- a/arch/x86/boot/Makefile
> +++ b/arch/x86/boot/Makefile
> @@ -65,7 +65,7 @@ clean-files += cpustr.h
>
> # ---------------------------------------------------------------------------
>
> -KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP
> +KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP -mno-red-zone
> KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
> GCOV_PROFILE := n
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 26050ae0b27e..e186cc0b628d 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -30,7 +30,7 @@ KBUILD_CFLAGS := -m$(BITS) -O2
> KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC)
> KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
> cflags-$(CONFIG_X86_32) := -march=i386
> -cflags-$(CONFIG_X86_64) := -mcmodel=small
> +cflags-$(CONFIG_X86_64) := -mcmodel=small -mno-red-zone
> KBUILD_CFLAGS += $(cflags-y)
> KBUILD_CFLAGS += -mno-mmx -mno-sse
> KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> @@ -87,7 +87,7 @@ endif
>
> vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
>
> -$(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
> +$(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar
>
> vmlinux-objs-$(CONFIG_EFI_STUB) += $(obj)/eboot.o \
> $(objtree)/drivers/firmware/efi/libstub/lib.a

That last chunk is not needed anymore after

c2d0b470154c ("efi/libstub/x86: Incorporate eboot.c into libstub")

AFAICT.

--
Regards/Gruss,
Boris.