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Subject[PATCH 4.4 061/266] powerpc/fsl: Flush the branch predictor at each kernel entry (64bit)
Date
From: Diana Craciun <diana.craciun@nxp.com>

commit 10c5e83afd4a3f01712d97d3bb1ae34d5b74a185 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/kernel/entry_64.S | 5 +++++
arch/powerpc/kernel/exceptions-64e.S | 26 +++++++++++++++++++++++++-
arch/powerpc/mm/tlb_low_64e.S | 7 +++++++
3 files changed, 37 insertions(+), 1 deletion(-)

--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -77,6 +77,11 @@ 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(r10, r11)
2: std r2,GPR2(r1)
std r3,GPR3(r1)
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -295,7 +295,8 @@ 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 */

@@ -327,6 +328,29 @@ 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))

--- a/arch/powerpc/mm/tlb_low_64e.S
+++ b/arch/powerpc/mm/tlb_low_64e.S
@@ -69,6 +69,13 @@ 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

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