[PATCH v7 12/72] x86/boot/compressed/64: Disable red-zone usage

Joerg Roedel
2020-09-07T13:15:13Z

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. Therefore, functions may use this area for 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, because the IRET frame
written by the hardware at the stack pointer and the functions to handle
the exception will overwrite the temporary variables of the interrupted
function, causing undefined behavior. So disable red-zones for the
pre-decompression boot code.

Signed-off-by: Joerg Roedel <jroedel at suse.de>
Reviewed-by: Kees Cook <keescook at chromium.org>
---
 arch/x86/boot/compressed/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/Makefile
b/arch/x86/boot/compressed/Makefile
index 871cc071c925..258a2fca6659 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -32,7 +32,7 @@ KBUILD_CFLAGS := -m$(BITS) -O2
 KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
 KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
 cflags-$(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 += -ffreestanding
--
2.28.0