powerpc/fsl: Flush the branch predictor at each kernel entry (64bit)

In order to protect against speculation attacks on
indirect branches, the branch predictor is flushed at
kernel entry to protect for the following situations:
- userspace process attacking another userspace process
- userspace process attacking the kernel
Basically when the privillege level change (i.e. the
kernel is entered), the branch predictor state is flushed.

Signed-off-by: Diana Craciun <diana.craciun@nxp.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/entry_64.S

@@ -80,6 +80,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
 	std	r0,GPR0(r1)
 	std	r10,GPR1(r1)
 	beq	2f			/* if from kernel mode */
+#ifdef CONFIG_PPC_FSL_BOOK3E
+START_BTB_FLUSH_SECTION
+	BTB_FLUSH(r10)
+END_BTB_FLUSH_SECTION
+#endif
 	ACCOUNT_CPU_USER_ENTRY(r13, r10, r11)
 2:	std	r2,GPR2(r1)
 	std	r3,GPR3(r1)

arch/powerpc/kernel/exceptions-64e.S

@@ -296,7 +296,8 @@ ret_from_mc_except:
 	andi.	r10,r11,MSR_PR;		/* save stack pointer */	    \
 	beq	1f;			/* branch around if supervisor */   \
 	ld	r1,PACAKSAVE(r13);	/* get kernel stack coming from usr */\
-1:	cmpdi	cr1,r1,0;		/* check if SP makes sense */	    \
+1:	type##_BTB_FLUSH		\
+	cmpdi	cr1,r1,0;		/* check if SP makes sense */	    \
 	bge-	cr1,exc_##n##_bad_stack;/* bad stack (TODO: out of line) */ \
 	mfspr	r10,SPRN_##type##_SRR0;	/* read SRR0 before touching stack */
 
@@ -328,6 +329,29 @@ ret_from_mc_except:
 #define SPRN_MC_SRR0	SPRN_MCSRR0
 #define SPRN_MC_SRR1	SPRN_MCSRR1
 
+#ifdef CONFIG_PPC_FSL_BOOK3E
+#define GEN_BTB_FLUSH			\
+	START_BTB_FLUSH_SECTION		\
+		beq 1f;			\
+		BTB_FLUSH(r10)			\
+		1:		\
+	END_BTB_FLUSH_SECTION
+
+#define CRIT_BTB_FLUSH			\
+	START_BTB_FLUSH_SECTION		\
+		BTB_FLUSH(r10)		\
+	END_BTB_FLUSH_SECTION
+
+#define DBG_BTB_FLUSH CRIT_BTB_FLUSH
+#define MC_BTB_FLUSH CRIT_BTB_FLUSH
+#define GDBELL_BTB_FLUSH GEN_BTB_FLUSH
+#else
+#define GEN_BTB_FLUSH
+#define CRIT_BTB_FLUSH
+#define DBG_BTB_FLUSH
+#define GDBELL_BTB_FLUSH
+#endif
+
 #define NORMAL_EXCEPTION_PROLOG(n, intnum, addition)			    \
 	EXCEPTION_PROLOG(n, intnum, GEN, addition##_GEN(n))
 

arch/powerpc/mm/tlb_low_64e.S

@@ -70,6 +70,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_EMB_HV)
 	std	r15,EX_TLB_R15(r12)
 	std	r10,EX_TLB_CR(r12)
 #ifdef CONFIG_PPC_FSL_BOOK3E
+START_BTB_FLUSH_SECTION
+	mfspr r11, SPRN_SRR1
+	andi. r10,r11,MSR_PR
+	beq 1f
+	BTB_FLUSH(r10)
+1:
+END_BTB_FLUSH_SECTION
 	std	r7,EX_TLB_R7(r12)
 #endif
 	TLB_MISS_PROLOG_STATS