[syslinux] [PATCH] Fix for crash with certain EFIs

[Chris Dragan]

Hello syslinux maintainers,

I came across the issue of syslinux crashing with some EFIs in the
UEFI boot mode.

Upon closer investigation it turned out that most object files which
go into syslinux efi64 are compiled with the so-called red zone. Some
EFIs follow Windows ABI more strictly and cause syslinux to crash due
to stack overwrite.

Looking at mk/efi.mk there was a previous attempt to fix it, but the
fix applied only to a handful of source files.

As far as I can tell (I may be wrong), the problem is limited to efi64
on x86_64 build and does not affect the efi32 and bios builds.

I see that a similar patch was proposed before in November 2015, but
for some reason it did not make it to the repository.

Please help fixing this bug.

Best Regards,
- Chris

PATCH:

Makefile: add -mno-red-zone to all efi64 objects

x86_64 EFI requires that all sources are compiled without red zone,
which is not supported by the Windows ABI.

Without this, syslinux crashes on some UEFI implementations.

--- syslinux-6.03-orig/mk/com32.mk
+++ syslinux-6.03/mk/com32.mk
@@ -29,6 +29,9 @@
 ifeq ($(strip $(ARCH)),x86_64)
        GCCOPT += $(call gcc_ok,-m64,)
        GCCOPT += $(call gcc_ok,-march=x86-64)
+ifdef EFI_BUILD
+       GCCOPT += $(call gcc_ok,-mno-red-zone)
+endif
        #let the stack-boundary default to whatever it is on 64bit
        #GCCOPT += $(call gcc_ok,-mpreferred-stack-boundary=8,)
        #GCCOPT += $(call gcc_ok,-incoming-stack-boundary=8,)
--- syslinux-6.03-orig/mk/efi.mk
+++ syslinux-6.03/mk/efi.mk
@@ -17,6 +17,9 @@
 endif
 ifeq ($(ARCH),x86_64)
        ARCHOPT = -m64 -march=x86-64
+ifdef EFI_BUILD
+       ARCHOPT = -mno-red-zone
+endif
        EFI_SUBARCH = $(ARCH)
 endif

@@ -29,7 +32,7 @@
                -I$(core)/include -I$(core)/ $(ARCHOPT) \
                -I$(com32)/lib/ -I$(com32)/libutil/include -std=gnu99 \
                -DELF_DEBUG -DSYSLINUX_EFI -I$(objdir) \
-               $(GCCWARN) -D__COM32__ -D__FIRMWARE_$(FIRMWARE)__
-mno-red-zone \
+               $(GCCWARN) -D__COM32__ -D__FIRMWARE_$(FIRMWARE)__ \
                -DLDLINUX=\"$(LDLINUX)\" -fvisibility=hidden \
                -Wno-unused-parameter $(GCCOPT)

--- syslinux-6.03-orig/mk/elf.mk
+++ syslinux-6.03/mk/elf.mk
@@ -27,6 +27,9 @@
 ifeq ($(ARCH),x86_64)
        GCCOPT += $(call gcc_ok,-m64,)
        GCCOPT += $(call gcc_ok,-march=x86-64)
+ifdef EFI_BUILD
+       GCCOPT += $(call gcc_ok,-mno-red-zone)
+endif
        #let preferred-stack-boundary be default (=4)
 endif
 GCCOPT += -Os -fomit-frame-pointer
--- syslinux-6.03-orig/mk/embedded.mk
+++ syslinux-6.03/mk/embedded.mk
@@ -30,6 +30,9 @@
 ifeq ($(ARCH),x86_64)
        GCCOPT := $(call gcc_ok,-m64)
        GCCOPT += $(call gcc_ok,-march=x86-64)
+ifdef EFI_BUILD
+       GCCOPT += $(call gcc_ok,-mno-red-zone)
+endif
        #let preferred-stack-boundary and incoming-stack-boundary be default(=4)
 # Somewhere down the line ld barfs requiring -fPIC
        GCCOPT += $(call gcc_ok,-fPIC)
--- syslinux-6.03-orig/mk/lib.mk
+++ syslinux-6.03/mk/lib.mk
@@ -12,6 +12,9 @@
 endif
 ifeq ($(ARCH),x86_64)
        GCCOPT += $(call gcc_ok,-m64,)
+ifdef EFI_BUILD
+       GCCOPT += $(call gcc_ok,-mno-red-zone)
+endif
        #let preferred-stack-boundary be default(=4)
        MARCH = x86-64
 endif