[PATCH v2] powerpc: Fix irq_soft_mask_set() and irq_soft_mask_return() with sanitizer

[Christophe Leroy]

In ppc, compiler based sanitizer will generate instrument instructions
around statement WRITE_ONCE(local_paca->irq_soft_mask, mask):

   0xc000000000295cb0 <+0>:	addis   r2,r12,774
   0xc000000000295cb4 <+4>:	addi    r2,r2,16464
   0xc000000000295cb8 <+8>:	mflr    r0
   0xc000000000295cbc <+12>:	bl      0xc00000000008bb4c <mcount>
   0xc000000000295cc0 <+16>:	mflr    r0
   0xc000000000295cc4 <+20>:	std     r31,-8(r1)
   0xc000000000295cc8 <+24>:	addi    r3,r13,2354
   0xc000000000295ccc <+28>:	mr      r31,r13
   0xc000000000295cd0 <+32>:	std     r0,16(r1)
   0xc000000000295cd4 <+36>:	stdu    r1,-48(r1)
   0xc000000000295cd8 <+40>:	bl      0xc000000000609b98 <__asan_store1+8>
   0xc000000000295cdc <+44>:	nop
   0xc000000000295ce0 <+48>:	li      r9,1
   0xc000000000295ce4 <+52>:	stb     r9,2354(r31)
   0xc000000000295ce8 <+56>:	addi    r1,r1,48
   0xc000000000295cec <+60>:	ld      r0,16(r1)
   0xc000000000295cf0 <+64>:	ld      r31,-8(r1)
   0xc000000000295cf4 <+68>:	mtlr    r0

If there is a context switch before "stb     r9,2354(r31)", r31 may
not equal to r13, in such case, irq soft mask will not work.

The same problem occurs in irq_soft_mask_return() with
READ_ONCE(local_paca->irq_soft_mask).

This patch partially reverts commit ef5b570d3700 ("powerpc/irq: Don't
open code irq_soft_mask helpers") with a more modern inline assembly.

Reported-by: Zhouyi Zhou <zhouzhouyi@xxxxxxxxx>
Fixes: ef5b570d3700 ("powerpc/irq: Don't open code irq_soft_mask helpers")
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
v2: Use =m constraint for stb instead of m constraint
---
 arch/powerpc/include/asm/hw_irq.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index 26ede09c521d..815420988ef3 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h
@@ -113,7 +113,11 @@ static inline void __hard_RI_enable(void)
 
 static inline notrace unsigned long irq_soft_mask_return(void)
 {
-	return READ_ONCE(local_paca->irq_soft_mask);
+	unsigned long flags;
+
+	asm volatile("lbz%X1 %0,%1" : "=r" (flags) : "m" (local_paca->irq_soft_mask));
+
+	return flags;
 }
 
 /*
@@ -140,8 +144,7 @@ static inline notrace void irq_soft_mask_set(unsigned long mask)
 	if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
 		WARN_ON(mask && !(mask & IRQS_DISABLED));
 
-	WRITE_ONCE(local_paca->irq_soft_mask, mask);
-	barrier();
+	asm volatile("stb%X0 %1,%0" : "=m" (local_paca->irq_soft_mask) : "r" (mask) : "memory");
 }
 
 static inline notrace unsigned long irq_soft_mask_set_return(unsigned long mask)
-- 
2.37.1