powerpc: Reject probes on instructions that can't be single stepped

Per the ISA, a Trace interrupt is not generated for:
- [h|u]rfi[d]
- rfscv
- sc, scv, and Trap instructions that trap
- Power-Saving Mode instructions
- other instructions that cause interrupts (other than Trace interrupts)
- the first instructions of any interrupt handler (applies to Branch and Single Step tracing;
CIABR matches may still occur)
- instructions that are emulated by software

Add a helper to check for instructions belonging to the first four
categories above and to reject kprobes, uprobes and xmon breakpoints on
such instructions. We reject probing on instructions belonging to these
categories across all ISA versions and across both BookS and BookE.

For trap instructions, we can't know in advance if they can cause a
trap, and there is no good reason to allow probing on those. Also,
uprobes already refuses to probe trap instructions and kprobes does not
allow probes on trap instructions used for kernel warnings and bugs. As
such, stop allowing any type of probes/breakpoints on trap instruction
across uprobes, kprobes and xmon.

For some of the fp/altivec instructions that can generate an interrupt
and which we emulate in the kernel (altivec assist, for example), we
check and turn off single stepping in emulate_single_step().

Instructions generating a DSI are restarted and single stepping normally
completes once the instruction is completed.

In uprobes, if a single stepped instruction results in a non-fatal
signal to be delivered to the task, such signals are "delayed" until
after the instruction completes. For fatal signals, single stepping is
cancelled and the instruction restarted in-place so that core dump
captures proper addresses.

In kprobes, we do not allow probes on instructions having an extable
entry and we also do not allow probing interrupt vectors.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f56ee979d50b8711fae350fc97870f3ca34acd75.1648648712.git.naveen.n.rao@linux.vnet.ibm.com

arch/powerpc/include/asm/ppc-opcode.h

@@ -130,6 +130,8 @@
 #define OP_PREFIX	1
 #define OP_TRAP_64	2
 #define OP_TRAP		3
+#define OP_SC		17
+#define OP_19		19
 #define OP_31		31
 #define OP_LWZ		32
 #define OP_LWZU		33
@@ -159,6 +161,20 @@
 #define OP_LD		58
 #define OP_STD		62
 
+#define OP_19_XOP_RFID		18
+#define OP_19_XOP_RFMCI		38
+#define OP_19_XOP_RFDI		39
+#define OP_19_XOP_RFI		50
+#define OP_19_XOP_RFCI		51
+#define OP_19_XOP_RFSCV		82
+#define OP_19_XOP_HRFID		274
+#define OP_19_XOP_URFID		306
+#define OP_19_XOP_STOP		370
+#define OP_19_XOP_DOZE		402
+#define OP_19_XOP_NAP		434
+#define OP_19_XOP_SLEEP		466
+#define OP_19_XOP_RVWINKLE	498
+
 #define OP_31_XOP_TRAP      4
 #define OP_31_XOP_LDX       21
 #define OP_31_XOP_LWZX      23
@@ -179,6 +195,8 @@
 #define OP_31_XOP_LHZUX     311
 #define OP_31_XOP_MSGSNDP   142
 #define OP_31_XOP_MSGCLRP   174
+#define OP_31_XOP_MTMSR     146
+#define OP_31_XOP_MTMSRD    178
 #define OP_31_XOP_TLBIE     306
 #define OP_31_XOP_MFSPR     339
 #define OP_31_XOP_LWAX      341

arch/powerpc/include/asm/probes.h

@@ -8,6 +8,7 @@
  * Copyright IBM Corporation, 2012
  */
 #include <linux/types.h>
+#include <asm/disassemble.h>
 
 typedef u32 ppc_opcode_t;
 #define BREAKPOINT_INSTRUCTION	0x7fe00008	/* trap */
@@ -31,6 +32,41 @@ typedef u32 ppc_opcode_t;
 #define MSR_SINGLESTEP	(MSR_SE)
 #endif
 
+static inline bool can_single_step(u32 inst)
+{
+	switch (get_op(inst)) {
+	case OP_TRAP_64:	return false;
+	case OP_TRAP:		return false;
+	case OP_SC:		return false;
+	case OP_19:
+		switch (get_xop(inst)) {
+		case OP_19_XOP_RFID:		return false;
+		case OP_19_XOP_RFMCI:		return false;
+		case OP_19_XOP_RFDI:		return false;
+		case OP_19_XOP_RFI:		return false;
+		case OP_19_XOP_RFCI:		return false;
+		case OP_19_XOP_RFSCV:		return false;
+		case OP_19_XOP_HRFID:		return false;
+		case OP_19_XOP_URFID:		return false;
+		case OP_19_XOP_STOP:		return false;
+		case OP_19_XOP_DOZE:		return false;
+		case OP_19_XOP_NAP:		return false;
+		case OP_19_XOP_SLEEP:		return false;
+		case OP_19_XOP_RVWINKLE:	return false;
+		}
+		break;
+	case OP_31:
+		switch (get_xop(inst)) {
+		case OP_31_XOP_TRAP:		return false;
+		case OP_31_XOP_TRAP_64:		return false;
+		case OP_31_XOP_MTMSR:		return false;
+		case OP_31_XOP_MTMSRD:		return false;
+		}
+		break;
+	}
+	return true;
+}
+
 /* Enable single stepping for the current task */
 static inline void enable_single_step(struct pt_regs *regs)
 {

arch/powerpc/kernel/kprobes.c

@@ -150,8 +150,8 @@ int arch_prepare_kprobe(struct kprobe *p)
 	if ((unsigned long)p->addr & 0x03) {
 		printk("Attempt to register kprobe at an unaligned address\n");
 		ret = -EINVAL;
-	} else if (IS_MTMSRD(insn) || IS_RFID(insn)) {
-		printk("Cannot register a kprobe on mtmsr[d]/rfi[d]\n");
+	} else if (!can_single_step(ppc_inst_val(insn))) {
+		printk("Cannot register a kprobe on instructions that can't be single stepped\n");
 		ret = -EINVAL;
 	} else if ((unsigned long)p->addr & ~PAGE_MASK &&
 		   ppc_inst_prefixed(ppc_inst_read(p->addr - 1))) {

arch/powerpc/kernel/uprobes.c

@@ -48,6 +48,11 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
 		return -EINVAL;
 	}
 
+	if (!can_single_step(ppc_inst_val(ppc_inst_read(auprobe->insn)))) {
+		pr_info_ratelimited("Cannot register a uprobe on instructions that can't be single stepped\n");
+		return -ENOTSUPP;
+	}
+
 	return 0;
 }
 

arch/powerpc/xmon/xmon.c

@@ -921,9 +921,9 @@ static void insert_bpts(void)
 			bp->enabled = 0;
 			continue;
 		}
-		if (IS_MTMSRD(instr) || IS_RFID(instr)) {
-			printf("Breakpoint at %lx is on an mtmsrd or rfid "
-			       "instruction, disabling it\n", bp->address);
+		if (!can_single_step(ppc_inst_val(instr))) {
+			printf("Breakpoint at %lx is on an instruction that can't be single stepped, disabling it\n",
+					bp->address);
 			bp->enabled = 0;
 			continue;
 		}
@@ -1470,9 +1470,8 @@ static long check_bp_loc(unsigned long addr)
 		printf("Can't read instruction at address %lx\n", addr);
 		return 0;
 	}
-	if (IS_MTMSRD(instr) || IS_RFID(instr)) {
-		printf("Breakpoints may not be placed on mtmsrd or rfid "
-		       "instructions\n");
+	if (!can_single_step(ppc_inst_val(instr))) {
+		printf("Breakpoints may not be placed on instructions that can't be single stepped\n");
 		return 0;
 	}
 	return 1;