Subject: [PATCH v4 20/20] powerpc/64e: Clear gprs on interrupt routine entry

From: Rohan McLure <[email-masked]>
Date: Wed, 24 Aug 2022 12:05:48 +1000

Zero GPRS r14-r31 on entry into the kernel for interrupt sources to
limit influence of user-space values in potential speculation gadgets.
Prior to this commit, all other GPRS are reassigned during the common
prologue to interrupt handlers and so need not be zeroised explicitly.

This may be done safely, without loss of register state prior to the
interrupt, as the common prologue saves the initial values of
non-volatiles, which are unconditionally restored in interrupt_64.S.

Signed-off-by: Rohan McLure <[email-masked]>
---
V3 -> V4: New patch.
---
 arch/powerpc/kernel/exceptions-64e.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index 48c640ca425d..296b3bf6b2a6 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -401,7 +401,8 @@ exc_##n##_common:							    \
 	std	r12,STACK_FRAME_OVERHEAD-16(r1); /* mark the frame */	    \
 	std	r3,_TRAP(r1);		/* set trap number		*/  \
 	std	r0,RESULT(r1);		/* clear regs->result */	    \
-	SAVE_NVGPRS(r1);
+	SAVE_NVGPRS(r1);						    \
+	ZEROIZE_NVGPRS();		/* minimise speculation influence */
 
 #define EXCEPTION_COMMON(n) \
 	EXCEPTION_COMMON_LVL(n, SPRN_SPRG_GEN_SCRATCH, PACA_EXGEN)
@@ -1068,6 +1069,7 @@ bad_stack_book3e:
 	std	r11,_CTR(r1)
 	std	r12,_XER(r1)
 	SAVE_NVGPRS(r1)
+	ZEROIZE_NVGPRS()
 	lhz	r12,PACA_TRAP_SAVE(r13)
 	std	r12,_TRAP(r1)
 	addi	r11,r1,INT_FRAME_SIZE
-- 
2.34.1