[PATCH] powerpc: Interrupt handler stack randomisation

[Rohan McLure <rmclure@linux.ibm.com>]

Stack frames used by syscall handlers support random offsets as of
commit f4a0318f278d (powerpc: add support for syscall stack randomization).
Implement the same for general interrupt handlers, by applying the
random stack offset and then updating this offset from within the
DEFINE_INTERRUPT_HANDLER macros.

Applying this offset perturbs the layout of interrupt handler stack
frames, rendering to the kernel stack more difficult to control by means
of user invoked interrupts.

Link: https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-May/243238.html

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
---
 arch/powerpc/include/asm/interrupt.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
index 4745bb9998bd..b7f7beff4e13 100644
--- a/arch/powerpc/include/asm/interrupt.h
+++ b/arch/powerpc/include/asm/interrupt.h
@@ -68,6 +68,7 @@
 
 #include <linux/context_tracking.h>
 #include <linux/hardirq.h>
+#include <linux/randomize_kstack.h>
 #include <asm/cputime.h>
 #include <asm/firmware.h>
 #include <asm/ftrace.h>
@@ -448,9 +449,12 @@ interrupt_handler long func(struct pt_regs *regs)			\
 	long ret;							\
 									\
 	__hard_RI_enable();						\
+	add_random_kstack_offset();					\
 									\
 	ret = ____##func (regs);					\
 									\
+	choose_random_kstack_offset(mftb());				\
+									\
 	return ret;							\
 }									\
 NOKPROBE_SYMBOL(func);							\
@@ -480,9 +484,11 @@ static __always_inline void ____##func(struct pt_regs *regs);		\
 interrupt_handler void func(struct pt_regs *regs)			\
 {									\
 	interrupt_enter_prepare(regs);					\
+	add_random_kstack_offset();					\
 									\
 	____##func (regs);						\
 									\
+	choose_random_kstack_offset(mftb());				\
 	interrupt_exit_prepare(regs);					\
 }									\
 NOKPROBE_SYMBOL(func);							\
@@ -515,9 +521,11 @@ interrupt_handler long func(struct pt_regs *regs)			\
 	long ret;							\
 									\
 	interrupt_enter_prepare(regs);					\
+	add_random_kstack_offset();					\
 									\
 	ret = ____##func (regs);					\
 									\
+	choose_random_kstack_offset(mftb());				\
 	interrupt_exit_prepare(regs);					\
 									\
 	return ret;							\
@@ -548,9 +556,11 @@ static __always_inline void ____##func(struct pt_regs *regs);		\
 interrupt_handler void func(struct pt_regs *regs)			\
 {									\
 	interrupt_async_enter_prepare(regs);				\
+	add_random_kstack_offset();					\
 									\
 	____##func (regs);						\
 									\
+	choose_random_kstack_offset(mftb());				\
 	interrupt_async_exit_prepare(regs);				\
 }									\
 NOKPROBE_SYMBOL(func);							\
@@ -585,9 +595,11 @@ interrupt_handler long func(struct pt_regs *regs)			\
 	long ret;							\
 									\
 	interrupt_nmi_enter_prepare(regs, &state);			\
+	add_random_kstack_offset();					\
 									\
 	ret = ____##func (regs);					\
 									\
+	choose_random_kstack_offset(mftb());				\
 	interrupt_nmi_exit_prepare(regs, &state);			\
 									\
 	return ret;							\
-- 
2.34.1