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

1 files changed, 36 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/probes.h b/arch/powerpc/include/asm/probes.h
index c5d984700d24..6f66e358aa37 100644
--- a/arch/powerpc/include/asm/probes.h
+++ b/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)
 {