[v6,09/15] arm64: reserve x18 from general allocation with SCS
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Message ID 20191206221351.38241-10-samitolvanen@google.com
State New
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Series
  • [v6,01/15] arm64: mm: avoid x18 in idmap_kpti_install_ng_mappings
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Commit Message

Sami Tolvanen Dec. 6, 2019, 10:13 p.m. UTC
Reserve the x18 register from general allocation when SCS is enabled,
because the compiler uses the register to store the current task's
shadow stack pointer. Note that all external kernel modules must also be
compiled with -ffixed-x18 if the kernel has SCS enabled.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 arch/arm64/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Will Deacon Jan. 16, 2020, 5:37 p.m. UTC | #1
On Fri, Dec 06, 2019 at 02:13:45PM -0800, Sami Tolvanen wrote:
> Reserve the x18 register from general allocation when SCS is enabled,
> because the compiler uses the register to store the current task's
> shadow stack pointer. Note that all external kernel modules must also be
> compiled with -ffixed-x18 if the kernel has SCS enabled.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> ---
>  arch/arm64/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)

Acked-by: Will Deacon <will@kernel.org>

Will

Patch
diff mbox series

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 1fbe24d4fdb6..e69736fc1106 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -72,6 +72,10 @@  stack_protector_prepare: prepare0
 					include/generated/asm-offsets.h))
 endif
 
+ifeq ($(CONFIG_SHADOW_CALL_STACK), y)
+KBUILD_CFLAGS	+= -ffixed-x18
+endif
+
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS	+= -mbig-endian
 CHECKFLAGS	+= -D__AARCH64EB__