[PATCH v2 06/13] powerpc: Support prefixed instructions in alignment handler

[Jordan Niethe <jniethe5@gmail.com>]

Alignment interrupts can be caused by prefixed instructions accessing
memory. In the alignment handler the instruction that caused the
exception is loaded and attempted emulate. If the instruction is a
prefixed instruction load the prefix and suffix to emulate. After
emulating increment the NIP by 8.

Prefixed instructions are not permitted to cross 64-byte boundaries. If
they do the alignment interrupt is invoked with SRR1 BOUNDARY bit set.
If this occurs send a SIGBUS to the offending process if in user mode.
If in kernel mode call bad_page_fault().

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
---
v2: - Move __get_user_instr() and __get_user_instr_inatomic() to this
commit (previously in "powerpc sstep: Prepare to support prefixed
instructions").
    - Rename sufx to suffix
    - Use a macro for calculating instruction length
---
 arch/powerpc/include/asm/uaccess.h | 30 ++++++++++++++++++++++++++++++
 arch/powerpc/kernel/align.c        |  8 +++++---
 arch/powerpc/kernel/traps.c        | 21 ++++++++++++++++++++-
 3 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 2f500debae21..30f63a81c8d8 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -474,4 +474,34 @@ static __must_check inline bool user_access_begin(const void __user *ptr, size_t
 #define unsafe_copy_to_user(d, s, l, e) \
 	unsafe_op_wrap(raw_copy_to_user_allowed(d, s, l), e)
 
+/*
+ * When reading an instruction iff it is a prefix, the suffix needs to be also
+ * loaded.
+ */
+#define __get_user_instr(x, y, ptr)			\
+({							\
+	long __gui_ret = 0;				\
+	y = 0;						\
+	__gui_ret = __get_user(x, ptr);			\
+	if (!__gui_ret) {				\
+		if (IS_PREFIX(x))			\
+			__gui_ret = __get_user(y, ptr + 1);	\
+	}						\
+							\
+	__gui_ret;					\
+})
+
+#define __get_user_instr_inatomic(x, y, ptr)		\
+({							\
+	long __gui_ret = 0;				\
+	y = 0;						\
+	__gui_ret = __get_user_inatomic(x, ptr);	\
+	if (!__gui_ret) {				\
+		if (IS_PREFIX(x))			\
+			__gui_ret = __get_user_inatomic(y, ptr + 1);	\
+	}						\
+							\
+	__gui_ret;					\
+})
+
 #endif	/* _ARCH_POWERPC_UACCESS_H */
diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
index ba3bf5c3ab62..e42cfaa616d3 100644
--- a/arch/powerpc/kernel/align.c
+++ b/arch/powerpc/kernel/align.c
@@ -293,7 +293,7 @@ static int emulate_spe(struct pt_regs *regs, unsigned int reg,
 
 int fix_alignment(struct pt_regs *regs)
 {
-	unsigned int instr;
+	unsigned int instr, suffix;
 	struct instruction_op op;
 	int r, type;
 
@@ -303,13 +303,15 @@ int fix_alignment(struct pt_regs *regs)
 	 */
 	CHECK_FULL_REGS(regs);
 
-	if (unlikely(__get_user(instr, (unsigned int __user *)regs->nip)))
+	if (unlikely(__get_user_instr(instr, suffix,
+				 (unsigned int __user *)regs->nip)))
 		return -EFAULT;
 	if ((regs->msr & MSR_LE) != (MSR_KERNEL & MSR_LE)) {
 		/* We don't handle PPC little-endian any more... */
 		if (cpu_has_feature(CPU_FTR_PPC_LE))
 			return -EIO;
 		instr = swab32(instr);
+		suffix = swab32(suffix);
 	}
 
 #ifdef CONFIG_SPE
@@ -334,7 +336,7 @@ int fix_alignment(struct pt_regs *regs)
 	if ((instr & 0xfc0006fe) == (PPC_INST_COPY & 0xfc0006fe))
 		return -EIO;
 
-	r = analyse_instr(&op, regs, instr, PPC_NO_SUFFIX);
+	r = analyse_instr(&op, regs, instr, suffix);
 	if (r < 0)
 		return -EINVAL;
 
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 82a3438300fd..d80b82fc1ae3 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -583,6 +583,10 @@ static inline int check_io_access(struct pt_regs *regs)
 #define REASON_ILLEGAL		(ESR_PIL | ESR_PUO)
 #define REASON_PRIVILEGED	ESR_PPR
 #define REASON_TRAP		ESR_PTR
+#define REASON_PREFIXED		0
+#define REASON_BOUNDARY		0
+
+#define inst_length(reason)	4
 
 /* single-step stuff */
 #define single_stepping(regs)	(current->thread.debug.dbcr0 & DBCR0_IC)
@@ -597,6 +601,10 @@ static inline int check_io_access(struct pt_regs *regs)
 #define REASON_ILLEGAL		SRR1_PROGILL
 #define REASON_PRIVILEGED	SRR1_PROGPRIV
 #define REASON_TRAP		SRR1_PROGTRAP
+#define REASON_PREFIXED		SRR1_PREFIXED
+#define REASON_BOUNDARY		SRR1_BOUNDARY
+
+#define inst_length(reason)	(((reason) & REASON_PREFIXED) ? 8 : 4)
 
 #define single_stepping(regs)	((regs)->msr & MSR_SE)
 #define clear_single_step(regs)	((regs)->msr &= ~MSR_SE)
@@ -1593,11 +1601,20 @@ void alignment_exception(struct pt_regs *regs)
 {
 	enum ctx_state prev_state = exception_enter();
 	int sig, code, fixed = 0;
+	unsigned long  reason;
 
 	/* We restore the interrupt state now */
 	if (!arch_irq_disabled_regs(regs))
 		local_irq_enable();
 
+	reason = get_reason(regs);
+
+	if (reason & REASON_BOUNDARY) {
+		sig = SIGBUS;
+		code = BUS_ADRALN;
+		goto bad;
+	}
+
 	if (tm_abort_check(regs, TM_CAUSE_ALIGNMENT | TM_CAUSE_PERSISTENT))
 		goto bail;
 
@@ -1606,7 +1623,8 @@ void alignment_exception(struct pt_regs *regs)
 		fixed = fix_alignment(regs);
 
 	if (fixed == 1) {
-		regs->nip += 4;	/* skip over emulated instruction */
+		/* skip over emulated instruction */
+		regs->nip += inst_length(reason);
 		emulate_single_step(regs);
 		goto bail;
 	}
@@ -1619,6 +1637,7 @@ void alignment_exception(struct pt_regs *regs)
 		sig = SIGBUS;
 		code = BUS_ADRALN;
 	}
+bad:
 	if (user_mode(regs))
 		_exception(sig, regs, code, regs->dar);
 	else
-- 
2.17.1