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Subject[PATCH 4.9 37/76] powerpc/fsl: Flush the branch predictor at each kernel entry (64bit)
Date
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: Sasha Levin <sashal@kernel.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(-)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 6625cec9e7c0..390ebf4ef384 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/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)
diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index ca03eb229a9a..79c6fee6368d 100644
--- 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))

diff --git a/arch/powerpc/mm/tlb_low_64e.S b/arch/powerpc/mm/tlb_low_64e.S
index eb82d787d99a..b7e9c09dfe19 100644
--- 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
--
2.19.1


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