[PATCH v5 2/7] powerpc/64: Add interrupt register sanitisation macros

[Rohan McLure]

Include in asm/ppc_asm.h macros to be used in multiple successive
patches to implement zeroising architected registers in interrupt
handlers. Registers will be sanitised in this fashion in future patches
to reduce the speculation influence of user-controlled register values.
These mitigations will be configurable through the
CONFIG_INTERRUPT_SANITIZE_REGISTERS Kconfig option.

Included are macros for conditionally zeroising registers and restoring
as required with the mitigation enabled. With the mitigation disabled,
non-volatiles must be restored on demand at separate locations to
those required by the mitigation.

Reviewed-by: Nicholas Piggin <npiggin at gmail.com>
Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
---
v4: New patch
v5: Remove unnecessary _ZEROIZE_ parts of macro titles, as the
implementation of how registers are sanitised doesn't need to be
immediately accessible, only that values will be clobbered. Introduce
arbitrary sanitize gpr(s) macros.
---
 arch/powerpc/include/asm/ppc_asm.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
index 753a2757bcd4..d2f44612f4b0 100644
--- a/arch/powerpc/include/asm/ppc_asm.h
+++ b/arch/powerpc/include/asm/ppc_asm.h
@@ -74,6 +74,25 @@
 #define SAVE_GPR(n, base)		SAVE_GPRS(n, n, base)
 #define REST_GPR(n, base)		REST_GPRS(n, n, base)
 
+/* macros for handling user register sanitisation */
+#ifdef CONFIG_INTERRUPT_SANITIZE_REGISTERS
+#define SANITIZE_SYSCALL_GPRS()			ZEROIZE_GPR(0);		\
+						ZEROIZE_GPRS(5, 12);	\
+						ZEROIZE_NVGPRS()
+#define SANITIZE_GPR(n)				ZEROIZE_GPR(n)
+#define SANITIZE_GPRS(start, end)		ZEROIZE_GPRS(start, end)
+#define SANITIZE_NVGPRS()			ZEROIZE_NVGPRS()
+#define SANITIZE_RESTORE_NVGPRS()		REST_NVGPRS(r1)
+#define HANDLER_RESTORE_NVGPRS()
+#else
+#define SANITIZE_SYSCALL_GPRS()
+#define SANITIZE_GPR(n)
+#define SANITIZE_GPRS(start, end)
+#define SANITIZE_NVGPRS()
+#define SANITIZE_RESTORE_NVGPRS()
+#define HANDLER_RESTORE_NVGPRS()		REST_NVGPRS(r1)
+#endif /* CONFIG_INTERRUPT_SANITIZE_REGISTERS */
+
 #define SAVE_FPR(n, base)	stfd	n,8*TS_FPRWIDTH*(n)(base)
 #define SAVE_2FPRS(n, base)	SAVE_FPR(n, base); SAVE_FPR(n+1, base)
 #define SAVE_4FPRS(n, base)	SAVE_2FPRS(n, base); SAVE_2FPRS(n+2, base)
-- 
2.37.2